Spectral position control of dye absorption band maximum in an orienting matrix

The continuous control of the maximum position of the dye absorption band (the zero of the derivative dD ()/d of the cell's optical density D ()) in a nematic matrix is demonstrated experimentally, as a result of changing the angle between the optical axis of a planar-oriented sample and the plane of polarization of absorbed light incident normal to the optical axis. The theory proposed describes quantitatively the experimental dependence (). The rotation of the polarizer with given frequency results in the spectral position modulation of the solute band maximum () within (=0°)–(90°)=700 cm^–1.     

Distance-constraint approach to protein folding. I. Statistical analysis of protein conformations in terms of distances between residues

A statistical analysis of protein conformations in terms of the distance between residues, represented by their C atoms, is presented. We consider four factors that contribute to the determination of the distanced _i,i+k between a given pair ofith and(i+k)th residues in the native conformation of a globular protein: (1) the distancek along the chain, (2) the size of the protein, (3) the conformational states of theith to(i+k)th residues, and (4) the amino acid types of the and(i+k)th residues. In order to account for the dependence on the distancek along the chain, the statistics are taken for three ranges, viz., short, medium, and long ranges (k8; 9k20; andk21; respectively). In the statistics of short-range distances, a mean distanceD _k and its standard deviationS _k are calculated for each value ofk, with and without taking into account the conformational states of all residues fromi toi+k (factors 1 and 3). As an Appendix, the relations for converting from the distances between residues into other conformational parameters are discussed. In the statistics of long-range distances, a reduced distanced* _ij (the actual distance divided by the radius of gyration) is used to scale the data so that they become independent of protein size, and then a mean reduced distanceD _l (a, a) and its standard deviation _l (a, a) are calculated for each amino acid pair (a, a) (factors 2 and 4). The effect of the neighboring residues along the chain on the value of the distanced* _ij is explored by a linear regression analysis between the actual reduced distanced* _ij and the mean value over theD _l for all possible pairs of residues in the two segments of the (i–2)th to the (i+2)th and the (j–2)th to the (j+2)th residues. The effect is assessed in terms of the tangentA _l (a, a) of the calculated regression line for each amino acid pair (a, a). In the statistics of medium-range distances, only factors 1 and 4 are considered, to simplify the analysis. The scaled distanced _i,i+k =(d _i,i+k -D _k )/S _k is used to eliminate the dependence onk, the distance along the chain. The propertiesD _m (a, a), _m (a, a) andA _m (a, a) corresponding toD _l (a, a), _l (a, a), andA _l (a, a), and also calculated for each amino acid pair (a, a). The results are interpreted as follows: the smaller values ofD _l (a, a) andD _m (a, a) indicate a preference of the pair (a, a) for a contact (e.g., pairs between hydrophobic amino acids, and pairs of Cys with aromatic amino acids), and the larger values of these quantities indicate a preference for distant mutual location (e.g., pairs between strong hydrophilic amino acids); the smaller values of _l (a, a) and _m (a, a) indicate a strong preference for either contact or noncontact (e.g., pairs between hydrophobic amino acids, and pairs between strong hydrophobic and hydrophilic amino acids, respectively), and the larger values of these quantities indicate the ambivalent/neutral nature of the preference for contact and noncontact (e.g., pairs containing Ser or Thr); the smaller values ofA _l (a, a) andA _m (a, a) indicate that the distance of an (a, a) pair is determined independently of the amino acid character of the neighboring residues along the chain (e.g., some pairs of Cys or Met with other amino acids) and the larger values of these quantities indicare that such amino acid character contributes strongly to the determination of the distance (e.g., pairs containing Ser or Thr, and pairs between amino acids with small side chains). The difference between the statistics for the long- and medium-range distances is also discussed; the former reflect the difference between the hydrophobic and hydrophilic character of the residues, but the latter cannot be easily interpretable only in terms of hydrophobicity and hydrophilicity. The data analyzed here are used in the optimization of an object function to compute protein conformation in a subsequent paper.     

Homonuclear chemical shift correlation in rotating solids via RN<Superscript>ν</Superscript><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> symmetry-based adiabatic RF pulse schemes

The efficacy of RN_n symmetry-based adiabatic Zero-Quantum (ZQ) dipolar recoupling schemes for obtaining chemical shift correlation data at moderate magic angle spinning frequencies has been evaluated. RN_n sequences generally employ basic inversion elements that correspond to a net 180° rotation about the rotating frame x-axis. It is shown here via numerical simulations and experimental measurements that it is also possible to achieve efficient ZQ dipolar recoupling via RN_n schemes employing adiabatic pulses. Such an approach was successfully used for obtaining ¹3C chemical shift correlation spectra of a uniformly labelled sample of (CUG)₉7– a triplet repeat expansion RNA that has been implicated in the neuromuscular disease myotonic dystrophy. An analysis of the ¹3C sugar carbon chemical shifts suggests, in agreement with our recent ¹5N MAS-NMR studies, that this RNA adopts an A-helical conformation.     

The quantitative analysis of chromosome pairing and chiasma formation based on the relative frequencies of M I configurations

Whilst reliable estimates of chiasma frequencies can usually not be obtained, the probability (b) of a chromosome arm to be bound by at least one chiasma can often be determined. In the absence of interference this probability equals (1–e ^–2), where 2 is the average chiasma frequency of the chromosome arm and the average crossover frequency or map length. In the presence of interference is shown to retain its genetic meaning as an additive metric that may describe the chromosome arm or other distinctive chromosome segment in terms of genetic recombination. It is a form of potential map length, comparable to, but numerically different from the regular map length. It is termed provisionally crossing-over potential.A chromosome with armsm andn with crossing-over potentials and will form ring bivalents with a frequency (1–e ^–2).(1–e ^–2); open bivalents with a frequency (1–e ^–2).e ^–2+(1–e ^–2).e ^–2; univalent pairs with a frequencye ^–2.e ^–2. Estimates of these frequencies yield equations from which and may be solved. In rye (Secale cereale) their ratio (q) is approximately two and differs from the mitotic arm length ratio of 1.4, indicating localization of chiasmata in the long arms.Graphs are given to show how, with constantq, the relation between the probabilitiesb _m andb _n of the two arms being bound changes with changing averageb.Data are presented on chiasma frequencies in M I, and compared with the frequencies expected in the absence of interference to give an impression of the degree of interference. Apparent fusion of chiasmata simulates interference.     

Kinetic sedimentation of Rhizobium-aggregates produced by leguminous lectins

Lectins from Canavalia brasiliensis (CnBr), Cratylia floribunda (CFL), Vatairea macrocarpa (VML) and Phaseolus vulgaris (PHA) aggregate Rhizobiumbacteria. The relationship between specific sedimentation rate, (based on bacterial dry biomass) of bacterial aggregates and lectin concentrations was hyperbolic and showed bacterial surface affinity by lectins. R. tropici (Rt), R. leguminosarum bv. phaseoli (Rlp) and R. etli (Re) surfaces showed predominantly receptors of galactosidic nature. The Rt surfaces showed very high affinities (k _s = ±8.6 × 10^–8 ag lectin protein ml^–1) by Gal-specific lectins (PHA and VML), and very low affinities (k_s=± 4.9 × 10^–6) by Glc-specific lectins (CnBr and CFL). The Rlp surface had intermediate affinities by lectins. The Re surface showed high affinities by PHA (k_s= ±1.26 × 10^–8) and intermediate affinities by VML, CnBr and CFL. The relationship between sedimentation specific (based on lectin weight) and bacterial density was a sigmoid and showed lectin affinity by Rt surfaces. The bacterial sedimentation showed positive cooperative binding of lectins. The V_max induced by Glc-specific lectins was ±20 of that produced by Gal-specific lectins. The PHA affinity (k_s= 1.19 mg dry biomass ml^–1) was larger than VML (k_s = 1.23). The Glc-specific lectin affinities were smaller than those of Gal-specific. The apparent binding site number of lectins (n_app) was: 2.7-PHA; 2.2-VML; 3.2-CFL and 3.2-CnBr. The dissociation constant, k_s, of lectin-binding kinetics decreased with sugar-hapten treatment (10 M). The n_app decreased in PHA and CFL, increasing in VML + sugar-hapten treatment. This study showed that there is a difference in Rhizobium surfaces for lectin binding.     

Characterization of NO adducts of the diiron center in protein R2 of<Emphasis Type="Italic"> Escherichia coli</Emphasis> ribonucleotide reductase and site-directed variants; implications for the O<Subscript>2 </Subscript>activation mechanism*

The R2 subunit of Escherichia coli ribonucleotide reductase contains a diiron site that reacts with O₂ to produce a tyrosine radical (Y122·). In wild-type R2 (R2-wt), the first observable reaction intermediate is a high-valent [Fe^III-Fe^IV] state called compound X, but in related diiron proteins such as methane monooxygenase, ⁹-desaturase, and ferritin, peroxodiiron(III) complexes have been characterized. Substitution of iron ligand D84 by E within the active site of R2 allows an intermediate (-1,2-peroxo)diiron species to accumulate. To investigate the possible involvement of a bridging peroxo species within the O₂ activation sequence of R2-wt, we have characterized the iron-nitrosyl species that form at the diiron sites in R2-wt, R2-D84E, and R2-W48F/D84E by using vibrational spectroscopy. Previous work has shown that the diiron center in R2-wt binds one NO per iron to form an antiferromagnetically coupled [{FeNO}⁷]₂ center. In the wt and variant proteins, we also observe that both irons bind one NO to form a {FeNO}⁷ dimer where both Fe–N–O units share a common vibrational signature. In the wt protein, (Fe–NO), (Fe–N–O), and (N–O) bands are observed at 445, 434 and 1742 cm^–1, respectively, while in the variant proteins the (Fe–NO) and (Fe–N–O) bands are observed ~10 cm^–1 higher and the (N–O) ~10 cm^–1 lower at 1735 cm^–1. These results demonstrate that all three proteins accommodate fully symmetric [{FeNO}⁷]₂ species with two identical Fe–N–O units. The formation of equivalent NO adducts in the wt and variant proteins strongly favors the formation of a symmetric bridging peroxo intermediate during the O₂ activation process in R2-wt.     

Elevated CO2 effects on carbon and nitrogen cycling in grass/clover turves of a Psammaquent soil

Effects of elevated CO₂ (525 and 700 L L^–1), and a control (350 L L^–1 CO₂), on biochemical properties of a Mollic Psammaquent soil in a well-established pasture of C3 and C4 grasses and clover were investigated with continuously moist turves in growth chambers over four consecutive seasonal temperature regimes from spring to winter inclusive. After a further spring period, half of the turves under 350 and 700 L L^–1 were subjected to summer drying and were then re-wetted before a further autumn period; the remaining turves were kept continuously moist throughout these additional three consecutive seasons. The continuously moist turves were then pulse-labelled with ¹⁴C-CO₂ to follow C pathways in the plant/soil system during 35 days.Growth rates of herbage during the first four seasons averaged 4.6 g m^–2 day^–1 under 700 L L^–1 CO₂ and were about 10% higher than under the other two treatments. Below-ground net productivity at the end of these seasons averaged 465, 800 and 824 g m^–2 in the control, 525 and 700 L L^–1 treatments, respectively.in continuously moist soil, elevated CO₂ had no overall effects on total, extractable or microbial C and N, or invertase activity, but resulted in increased CO₂-C production from soil, and from added herbage during the initial stages of decomposition over 21 days; rates of root decomposition were unaffected. CO₂ produced h^–1 mg^–1 microbial C was about 10% higher in the 700 L L^–1 CO₂ treatment than in the other two treatments. Elevated CO₂ had no clearly defined effects on N availability, or on the net N mineralization of added herbage.In the labelling experiment, relatively more ¹⁴C in the plant/soil system occurred below ground under elevated CO₂, with enhanced turnover of ¹⁴C also being suggested.Drying increased levels of extractable C and organic-N, but decreased mineral-N concentrations; it had no effect on microbial C, but resulted in lowered microbial N in the control only. In soil that had been previously summer-dried, CO₂ production was again higher, but net N mineralization was lower, under elevated CO₂ than in the control after autumn pasture growth.Over the trial period of 422 days, elevated CO₂ generally appears to have had a greater effect on soil C turnover than on soil C pools in this pasture ecosystem.     

Redox control of proton transfers in membrane b-type cytochromes: an absorption and resonance Raman study on bis(imidazole) and bis(imidazolate) model complexes of iron-protoporphyrin

Optical absorption spectra and resonance Raman (RR) spectra, obtained with Soret excitation, are reported for bis(imidazole) and bis(imidazolate) complexes of iron(II)- and iron(III)-protoporphyrin IX, prepared in aqueous conditions. Perdeuteration experiments on the axial ligands permitted the assignment of the symmetric Fe-(ligand)₂ stretching mode of Fe[x]PP(L)₂ to RR bands at 203 (x = II; L = ImH), 212 (x = II; L = Im^–), 201 (x = III; L = ImH) and 226 cm^–1 (x = III; L = Im^–). These frequency differences indicate a strengthening of the axial bonds when the imidazole deprotonations occur. The larger difference observed for the ferric derivatives reflects the stronger -donor capability of the Im^– anion for iron(III) over iron(II). For the ferrous derivatives, the frequencies of several skeletal porphyrin modes (₄, ₁₀, ₁₁ and ₃₈) are downshifted by 2–10 cm^–1 upon deprotonation of the ligands. This effect corresponds to an increased back-bonding from the metal atom to the porphyrin ring when the axial ligand decreases its -acid strength. Bringing further support to this interpretation, an inverse linear relationship is established between the frequencies of (Fe(Il)-L₂) and ₁₁. This correlation is expected to monitor the overall H-bonding state of histidine ligands of reduced cytochromes b. On the other hand, absorption measurements have characterized large pK_a differences for the sequential imidazole ionizations of Fe[x]PP(ImH)₂ in aqueous cetyltrimethylammonium bromide (9.0 and 10.8 for x = 111; 13.0 and 14.1 for x = II). These titrations show that Fe(II)PP(Im^–)₂ and Fe(III)PP(ImH)₂ are good proton-acceptor and proton-donor, respectively, and suggest a model by which heme, located in a favorable environment inside a cytochrome, could couple a cycle of electron transfer with a proton transfer. Based on sequence data and structural models, it is further proposed that, in several membrane cytochromes b (b, b ₆, b ₅₅₉), a positively charged amino acid residue and an imidazolate ligand of the ferriheme could form an ion pair involved in a redox control of proton transfer.Abbreviations RR resonance Raman - EPR electron paramagnetic resonance - PP protoporphyrin IX - ImH imidazole - Im^– imidazolate - Im* imidazole or imidazolate - 1MeIm 1-methylimidazole - HisH histidine - His^– histidinate - CTABr cetyltrimethylammonium bromide - NaDS sodium dodecylsulphate - VLP very low potential - LP low potential - HP high potential     

Inhibition of ADP-ribosylation of histone H1 by analogs of diadenosine 5′, 5‴-p1,p4-tetraphosphate

The effects of analogs of diadenosine 5,5-p¹,p⁴-tetraphosphate (Ap4A) were examined on the ADP-ribosylation reaction of histone Hl catalysed by purified bovine thymus poly(ADP-ribose)transferase. Among the compounds tested, Ap4A and ApCH₂PPPA were shown to be the most efficient inhibitors of the enzyme. From kinetic studies of their action, it appears that Ap4A and ApCH₂pppA might be mixed type inhibitors.Abbreviations ADP-ribose adenosine diphosphate ribose - ADPRT poly-(ADP-ribose)transferase - Ap4A diadenosine 5,5-p₁,p₄-tertraphosphate - Ap4A diadenosine 5,5-p¹,p⁴(-1,N⁶-ethenyl-)tetra-phosphate - ApAA diadenosine 5,5-p¹,p⁴(-N⁶(-1,N⁶-)bisethenyl-)tetraphosphate - ApCH₂pppA diadenosine 5,5-p¹,p⁴(-p¹,p²-methylene-)tetraphosphate - AppCH₂ppA diadenosine 5,5-p¹,p⁴(-p²,p³methylene-)tetraphosphate - AppNHppA diadenosine 5,5-p¹,p⁴(-p²,p³-amino-)tetraphosphate - AppCHBrppA diadenosine 5,5-p¹,p⁴(-p²,p³-bromine methyno-)tetraphosphate - CpCH₂ppCH₂PC dicytidine 5,5-p¹,p⁴(-p¹,p²-p³,p⁴-bismethylene-)tetraphosphate - ApCH₂ppCH₂pA diadenosine 5,5-p¹,p⁴(-p¹,p²-p³,p⁴-bismethylene-)tetraphosphate.     

Effects of ganglioside GM1 on the thermotropic behavior of cholera toxin B subunit

Summary The B, or binding, subunit of cholera enterotoxin forms a pentameric ring structure in the intact toxin, and also when the subunit is isolated from the A subunit. The thermal denaturation of the B subunit ring was examined by differential scanning calorimetry in the presence and absence of ganglioside G_M1, its natural receptor. In the absence of ganglioside an irreversible endotherm was observed with maximal excess apparent heat capacity, C_max, at 74.6° C. When the ganglioside was added in increasing amounts, multiple transitions were observed at higher temperatures, the most prominent having a C_max at 90.8° C. At high ganglioside concentrations, the 74.6° C transition was not observed. In addition to the thermodynamic results a model is proposed for the interaction of G_M1 and B subunit pentamer. This model is derived independently of the calorimetric results (but is consistent with such data) and is based upon considerations of the geometry of the G_M1 micelle-B subunit pentamer.Abbreviations M_r molecular weight in daltons - G_M1 H³Neu-AcGgOse₄Cer^* = Gall 3Ga1NAc1 4Gal-[3 - 2NeuAc]1 4Glc1 1Cer (asterisked form follows the recommendations of the IUPACIUB Commission on Biochemical Nomenclature, Ref. 3) - R molar ratio of G_M1 to B monomer - DSC differential scanning calorimetry - C_max excess apparent heat capacity - C_max maximal value of C_ex - t_m temperature (° C) at C_ex = C_max - t_1/2 peak width in °C at C_ex = C_max/2 - H_cal calorimetric enthalpy - C _p ^d van't Hoff enthalpy - C _p ^d change in specific heat accompanying denaturation     

Diagnosing lactic acid fermentation based on specific rates of growth,substrate consumption and product formation

The on-line calculated specific rates of growth, substrate consumption and product formation were used to diagnose microbial activities during a lactic acid fermentation. The specific rates were calculated from on-line measured cell mass, and substrate and product concentrations. The specific rates were more sensitive indicators of slight changes in fermentation conditions than such monitored data as cell mass or product concentrations.List of Symbols 1/h specific rate of cell growth - 1/h specific rate of substrate consumption - 1/h specific rate of product formation - ^* dimensionless specific rate of cell growth - ^* dimensionless specific rate of substrate consumption - ^* dimensionless specific rate of product formation - _max 1/h maximum specific rate of cell growth - _max 1/h maximum specific rate of substrate consumption - _max 1/h maximum specific rate of product formation - X g/l cell mass concentration - S g/l substrate concentration - S ^* dimensionless substrate concentration - S ₀ g/l initial substrate concentration - P g/l product concentration     

Calcium-induced associations of the caseins: Thermodynamic linkage of calcium binding to colloidal stability of casein micelles

The caseins occur in milk as colloidal complexes of protein aggregates, calcium, and inorganic phosphate. As determined by electron microscopy, these particles are spherical and have approximately a 650 Å radius (casein micelles). In the absence of calcium, the protein aggregates themselves (submicelles) have been shown to result from mainly hydrophobic interactions. The fractional concentration of stable colloidal casein micelles can be obtained in a calcium caseinate solution by centrifugation at 1500g. Thus, the amount of stable colloid present with varying Ca²⁺ concentrations can be determined and then analyzed by application of equations derived from Wyman's Thermodynamic Linkage Theory. Ca²⁺-induced colloid stability profiles were obtained experimentally for model micelles consisting of only _s1- (a calcium insoluble casein) and the stabilizing protein -casein, eliminating the complications arising from - and minor casein forms. Two distinct genetic variants _s1-A andB were used. Analysis of _s1-A colloid stability profiles yielded a precipitation (salting-out) constantk ₁, as well as colloid stability (salting-in) parameterk ₂. No variations ofk ₁ ork ₂ were found with increasing amounts of -casein. From the variation of the amount of colloidal casein capable of being stabilized vs. amount of added -casein an association constant of 4 L/g could be calculated for the complexation of _s1-A and -casein. For the _s1-B and -casein micelles, an additional Ca²⁺-dependent colloidal destabilization parameter,k ₃, was added to the existingk ₁ andk ₂ parameters in order to fully describe this more complex system. Furthermore, the value ofk ₃ decreased with increasing concentration of -casein. These results were analyzed with respect to the specific deletion which occurs in _s1-caseinA in order to determine the sites responsible for these Ca²⁺-induced quaternary structural effects.     

Bubble column bioreactors

Summary The photographic and electrical conductivity methods to measure the structure of two phase flow, especially bubble size, bubble frequency, local gas hold-up and, for the latter, the bubble velocity are described.Symbols specific interfacial area - a gas/liquid interfacial area - B constant in Eq. (4) - d diameter of the bubbles - d mean diameter of the bubbles - d_S Sauter diameter - E_G relative gas hold up - I current - k_L mass transfer coefficient across the gas/liquid interface - k_L local k_L - LT^–1 - LT^–1 - 1 longitudinal distance between the start and stop sensors - 1_B pierced length of the bubble - t time - t₁ length of the square-wave signal at the start sensor - t₂ length of the square-wave signal at the stop sensor - t₁₂ time delay between start and stop signals - V volume of the bubbling layer - V_L volume of the bubble free layer - V_B bubble volume - v_B bubble velocity     

Elevated CO2 and temperature effects on soil carbon and nitrogen cycling in ryegrass/white clover turves of an Endoaquept soil

Effects of elevated CO₂ (700 L L^–1) and a control (350 L L^–1 CO₂) on the productivity of a 3-year-old ryegrass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700 L L^–1 CO₂ and a temperature 6°C higher throughout than in the other treatments, was included.Under the same temperature conditions, overall herbage yields in the 700 L L^–1 CO₂ treatment were ca. 7% greater than in the control at the end of the summer period. Root mass (to ca 25 cm depth) in the 700 L L^–1 CO₂ treatment was then about 50% greater than in the control, but in the 700 L L^–1 CO₂+6°C treatment it was 6% lower than in the control. Based on decomposition results, herbage from the 700 L L^–1+6°C treatment probably contained the highest proportion of readily decomposable components.Elevated CO₂ had no consistent effect on soil total C and N, microbial C and N, or extractable C concentrations in any of the treatments. Under the same temperature conditions, it did, however, enhance soil respiration (CO₂-C production) and invertase activity. The effects of elevated CO₂ on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO₂, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials.Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO₂ enrichment is, nevertheless, indicated. Futher long-term experiments are required to determine the overall effect of elevated CO₂ on the soil C balance.     

Antibacterial Effects of Water-Soluble Low-Molecular-Weight Chitosans on Different Microorganisms

Low-molecular-weight chitosans with a viscosity-average molecular weight (M) of 5 to 27 kDa and an equal degree of deacetylation (DD, 85%) were highly active against Pseudomonas aureofaciens, Enterobacter agglomerans, Bacillus subtilis, and Bifidobacterium bifidum791, causing death in 80 to 100% of cells. An exception to this tendency was Escherichia coli, for which the rate of cell death induced by the 5-kDa chitosan, was 38%. The antibacterial effect was manifested as early as 10 min after the incubation of 12-kDa chitosan with B. subtilis or E. coli cells. Candida krusei was almost insensitive to the above crab chitosans. However, Candida krusei was highly sensitive to chitosans with M 5, 6, 12, 15.7, and 27 kDa: the minimum inhibitory concentration (MIC) varied from 0.06 to 0.005%. Chitosans with M 5, 12, and 15.7 kDa exerted an antibacterial effect on Staphylococcus aureus. Chitosans with M 5, 15.7, and 27 kDa had no effect on Bifidobacterium bifidum ATCC 14893. The antibacterial effect of the 4-kDa chitosan on E. coli and B. bifidum 791 increased with DD in the range 55–85%.     

Kinetic studies of peptide bond formation. Effect of chloramphenicol

There might be an undetermined order in the interaction of the substrates with the ribosomes in the reaction of CACCA-Leu-Ac with puromycin to form Ac-Leu-puromycin and CACCA (fragment reaction). Km 0°=6×10^-4 M for the puromycin · ribosome interaction. Chloramphenicol totally blocks the fragment reaction as a consequence of a single interaction with the ribosome of Kd 0°=2.2×10^-6 M. The inhibition by chloramphenicol of the fragment reaction is mixed competitive for puromycin.     

Contribution of methanol to the production of methane and its <Superscript>13</Superscript>C-isotopic signature in anoxic rice field soil

Conversion of methanol to CH₄ has a large isotope effect so that a small contribution of methanol-dependent CH₄ production may decrease the ¹³CH₄ of total CH₄ production. Therefore, we investigated the role of methanol for CH₄ production. Methanol was not detectable above 10 M in anoxic methanogenic rice field soil. Nevertheless, addition of ¹³C-labeled methanol (99% enriched) resulted in immediate accumulation of ¹³CH₄. Addition of 0.1 M ¹³C-methanol resulted in increase of the ¹³CH₄ from –47 to –6 within 2 h, followed by a slow decrease. Addition of 1 M ¹³C-methanol increased ¹³CH₄ to +500 within 4 h, whereas 10 M increased ¹³CH₄ to +2500 and continued to increase. These results indicate that the methanol concentrations in situ, which diluted the ¹³C-methanol added, were 0.1 M and that the turnover of methanol contributed only about 2% to total CH₄ production at 0.1 M. However, contribution increased up to 5 and 17% when 1 and 10 M methanol were added, respectively. Anoxic rice soil that was incubated at different temperatures between 10 and 37 °C exhibited maximally 2–6% methanol-dependent methanogenesis about 1–2 h after addition of 1 M ¹³C-methanol. Only at 50 °C, contribution of methanol to CH₄ production reached a maximum of 10%. After longer (7–10 h) incubation, however, contribution generally was only 2–4%. Methanol accumulated in the soil when CH₄ production was inhibited by chloroform. However, the accumulated methanol accounted for only up to 0.7 and 1.2% of total CH₄ production at 37 and 50 °C, respectively. Collectively, our results show that methanol-dependent methanogenesis was operating in anoxic rice field soil but contributed only marginally to total CH₄ production and the isotope effect observed at both low and high temperature.     

Contrasting oxygen-effects in the inactivation of ribonuclease A by N 3 ⋅ , (SCN) 2 ⋅ − and⋅OH radicals

Summary N ₃ exhibits higher efficiency thanOH in the inactivation of RNase in de-acerated (neutral) aqueous solution. In O₂-saturated solution theOH-induced inactivation is enhanced, but N ₃ and (SCN) ₂ ^– become remarkably inefficient. Our results suggest that semi-oxidized tyrosine, the predominant initial defect induced by N ₃ and (SCN) ₂ ^– but not byOH, can be re-reduced upon reaction with O ₂ ^– or cysteine.     

Alcoholic fermentation by Zymomonas mobilis: Effect of initial substrate on physiological parameters

Summary The influence of initial substrate concentration on fermentation kinetics of Zymomonas mobilis on glucose has been studied in batch cultures over the range 50–190 gl^-1 glucose. With increasing glucose, parameters relative to growth ( and R_GX) are more rapidly and more noticeably affected than those connected with ethanol production (p and R_GP). The water content of the cells is also affected.