Mn2+ reduces Yz + in manganese-depleted Photosystem II preparations

Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn²⁺. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Y_z ⁺, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Y_z ⁺ reduction by benzidine was a linear function of benzidine concentration. The rate of Y_z ⁺ reduction by Mn²⁺ at pH 6 increased linearly at low Mn²⁺ concentrations and reached a maximum at the Mn²⁺ concentrations equal to several times the reaction center concentration. The rate was inhibited by K⁺, Ca²⁺ and Mg²⁺. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Y_z ⁺ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn²⁺ near Y_z ⁺ at a site that may be one of the native manganese binding sites.Abbreviations PS II Photosystem II - Y_D tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum - Y_z tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation - ESR electron spin resonance - DPC diphenylcarbazide - DCIP dichlorophenolindophenol     

Growth and shoot formation in protoplast-derived calli of Brassica oleracea ssp. acephala and ssp. capitata

The effect of media components and environmental factors on growth and organogenesis of protoplast-derived calli of curly kale and cabbage were tested. Optimal growth (fresh weight increase of calli, shoots and roots) was found at 60 mM sucrose. Lower sucrose concentrations (3–30 mM) were favourable for shoot formation. Nitrate concentrations from 23 to 100 mM in combination with 8 or 21 mM ammonium were optimal for shoot formation. However, growth was reduced by high (100 mM) nitrate concentration. The effects of various organic nitrogen compounds at 0.5 and 2 mM were tested. Glutamine did not influence shoot formation and barely growth. Proline at 0.5 mM stimulated growth of cabbage calli but decreased growth of curly kale calli, and at 2 mM, proline also inhibited shoot production. Adenine sulphate decreased growth of cabbage calli at 0.5 mM, and at 2 mM shoot production was also reduced. Spermidine and spermine inhibited both growth and differentiation. Putrescine resulted in about 50% higher fresh weights, and also increased the number of calli producing shoots by about 35%. More calli produced shoots in white light than in blue or red light or in darkness. The length of the photoperiod or intensity of light was not critical for shoot production.     

Effects of nucleotides and divalent cations on phospholipase activity in Saccharomyces cerevisiae

Divalent cations activate the lysophospholipase and transacylase reactions catalyzed by the same enzymes in the yeast Saccharomyces cerevisiae. The activation was observed at neutral pH, but not at the pH optimum of lysophospholipase/transacylase, near 3.5. Adenine nucleotides, especially AMP and ADP, are strong inhibitors of the same group of enzymes. Half maximal inhibition by AMP was found at a concentration of about 20 M. The inhibition by nucleotides in low concentrations is enhanced by divalent cations.     

Regulation of branched-chain amino acid biosynthesis in Streptomyces fradiae,a producer of tylosin

Synthesis of threonine dehydratase in Streptomyces fradiae was positively influenced by valine and negatively by isoleucine. However, these two amino acids had no effect on the activity of this enzyme. Synthesis of threonine dehydratase in -aminobutyrate resistant mutants of S. fradiae was pronouncedly less sensitive to the positive effect of valine and this change in regulation led to valine overproduction. Synthesis of acetohydroxy acid synthase is regulated in a similar manner to that of threonine dehydratase, however a lower level of expression was detected in -aminobutyrate resistant mutants. And again, no effect of branched-chain amino acids on acetohydroxy acid synthase activity was observed. It follows that in S. fradiae synthesis of threonine dehydratase is the main regulatory mechanism governing production and the mutual ratio of synthesized valine and isoleucine.Abbreviations -AB -aminobutyrate - AHAS acetohydroxy acid synthase - -KB -ketobutyrate - MNNG N-methyl-N-nitro-N-nitrosoguanidine - TD threonine dehydratase - Trans. B. transaminase of branched-chain amino acids - VDH valine dehydrogenase     

Nontoxic and toxic oligopeptides with D-amino acids and unusual residues in Microcystis aeruginosa PCC 7806

Toxic and nontoxic peptides were isolated from the cyanobacterium Microcystis aeruginosa PCC 7806 by a procedure including extraction of cells with water-saturated 1-butanol, chromatography of the extract on silica gel plates and high performance liquid chromatography (HPLC) on Partisil-5. The toxin was shown to be only a minor constituent, being negatively charged and thus separable by electrophoresis, within the HPLC-purified fraction. It contained erythro-β-methyl-D-Asp, D-Glu, D-Ala, L-Leu, and L-Arg known to be part of the Microcystis peptide-toxin with M_r 994. The major part of the HPLC-purified fraction was assigned, however, to a nontoxic peptide with a M_r of 956. Partial hydrolysis studies of the nontoxic peptide(s) revealed amino acid sequences composed of D-Glu, N-methyl-Phe, and 3,4-dehydro-Pro, aside from the common L-amino acids. Cyclic linkage in the nontoxic peptide(s) appears likely.     

Glandular trichome exudate is the critical factor in geranium resistance to foxglove aphid

Resistance to the foxglove-aphid (Acyrthosiphon solani Kaltenbach) has been demonstrated in some inbred geranium lines (Pelargonium Xhortorum Bailey). To establish more definitively the cause/effect relationship between tall glandular trichome exudate and resistance, an intact plant bioassay was performed comparing a resistant plant line, a resistant plant line from which the tall glandular trichome exudate had been removed using a basic buffer solution, a susceptible line and a susceptible line treated with the buffer wash. After 5 days of isolation on the respective surfaces, the number of surviving adult aphids as well as the number of nymphs produced and remaining alive were determined. Aphids on the buffer washed, resistant line exhibited mortality and fecundity which was not significantly different from that produced by the susceptible line. In contrast, the untreated resistance line was clearly resistant with lower adult survival and fewer living nymphs. The tall glandular trichome exudate must therefore be a critical factor in geranium resistance to the foxglove aphid.

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Zusammenfassung Widerstandsfähigkeit dem Fingerhut-Blattlaus (Acyrthosiphon solani Kaltenbach) gegenüber wurde in einigen durch Inzucht erzeugten Pelargonie-Linien (Pelargonium Xhortorum Bailey) gezeigt. Um das Verhältnis von Ursache und Wirkung zwischen dem hochgewachsenen glandulären Trichom-Exudat und Widerstandsfähigkeit genauer zu bestimmen, wurde eine Bio-Untersuchung an intakten Pflanzen unternommen. Dabei wurden eine widerstandsfähige Pflanzenlinie, eine widerstandsfähige Pflanzenlinie, von der das hochgewachsene glanduläre Trichom-Exudat durch eine basische Pufferlösung entfernt worden war, eine anfällige Linie und eine mit Pufferlösung behandelte Linie verglichen. Zwei erwachsene weibliche Blattläuse wurden fünf Tage durch ein engmaschiges Netz auf den zu untersuchenden dritten und vierten Knotenblättern eingesperrt. Bei jeder Pflanze wurde die Untersuchung an einem nichtbehandelten Blatt und an einem Blat, von dem das Exudat durch Waschen mit der Pufferlösung entfernt worden war, durchgeführt. Für jede Linie wurden fünf Pflanzen gebraucht, und der ganze Versuch wurde sechsmal wiederholt. Nach einer fünftägigen Isolierung auf den jeweiligen Oberflächen wurden die Blätter von der Pflanze entfernt, und sowohl die Zahl der überlebenden erwachsenen Blattläuse wie auch die der produzierten und noch am Leben gebliebenen Nymphen festgestellt. Mit einer niedrigeren Überlebensrate der Erwachsenen und weniger noch lebenden Nymphen war die nichtbehandelte widerstandsfähige Linie deutlich widerstandsfähig. Im Gegensatz dazu zeigten die Blattläuse auf der mit Puffer gewaschenen widerstandsfähigen Linie eine Sterblichkeit und Fruchtbarkeit, die nicht erheblich höher waren, als die auf der anfälligen Linie, was beweist, daß das Waschen mit der Pufferlösung den Widerstandsfaktor entfernt hatte. Das hochgewachsene glanduläre Trichom-Exudat muß deshalb ein kritischer Faktor in der Widerstandsfähigkeit gegen Pelargonie-Schädlinge sein.

     

Secondary transport of amino acids by membrane vesicles derived from lactic acid bacteria

Lactococci are fastidious bacteria which require an external source of amino acids and many other nutrients. These compounds have to pass the membrane. However, detailed analysis of transport processes in membrane vesicles has been hampered by the lack of a suitable protonmotive force (pmf)-generating system in these model systems. A membrane-fusion procedure has been developed by which pmf-generating systems can be functionally incorporated into the bacterial membrane. This improved model system has been used to analyze the properties of amino acid transport systems in lactococci. Detailed studies have been made of the specificity and kinetics of amino acid transport and also of the interaction of the transport systems with their lipid environment. The properties of a pmf-independent, arginine-catabolism specific transport system in lactococci will be discussed.Abbreviations pmf protonmotive force - transmembrane electrical potential - pH transmembrane pH gradient - PE phosphatidylethanolamine - PC phosphatidylcholine Paper adapted from a treatise Secondary Transport of Amino Acids by Membrane Vesicles Derived from Lactic Acid Bacteria and awarded the Kluyver Prize 1988 by the Netherlands Society of Microbiology.     

Impact of salt adaptation on esterified fatty acids and cytochrome oxidase in plasma and thylakoid membranes from the cyanobacterium Anacystis nidulans

During adaptation of photoautotrophically growing fresh water cyanobacterium Anacystis nidulans to high salinity the cells showed a pronounced increase of proton-sodium antiporter activity, and of cytochrome c oxidase in isolated and purified plasma membrane. At the same time the concentrations of plasma membrane-bound EDTA-resistant copper and iron (determined by inductively coupled plasma atomic emission spectrometry) rose proportionately, accompanied by an increase in whole cell respiration. In plasma membranes from salt adapted cells lipid/protein ratios were markedly higher than in control cells, levels of esterified saturated and long-chain fatty acids being significantly higher than the respective levels of unsaturated and short-chain fatty acids which explains the higher lipid-phase transition temperatures derived from Arrhenius plots. Immunoblotting of the membrane proteins with antisera raised against the cytochrome c oxidases from Paracoccus denitrificans and A. nidulans gave two cross-reacting bands with apparent molecular weights around 50000 and 30000 (subunits I and II, respectively) which were more pronounced in plasma membranes from salt adapted cells when compared to control cells. The protein pattern of plasma membranes from salt adapted cells also showed the appearance of bands at apparent molecular weights of 44000–48000 and 54000–56000 which might stem from the proton/sodium-antiporter in this membrane.Abbreviations CM cytoplasmic or plasma membrane - ICM intracytoplasmic or thylakoid membrane - cyt cytochrome - DCCD N,N-dicyclohexylcarbodiimide - Hepes N-2-hydroxyethylpiperazine-N-2-ethanesulfonate - ICP-AES inductively coupled plasma atomic emission spectrometry - SDS-PAGE sodium dodecylsulfate polyacrylamide gel electrophoresis - EPR electron paramagnetic resonance spectrometry     

Energetics of syntrophic ethanol oxidation in defined chemostat cocultures

The ethanol-oxidizing, proton-reducing Pelobacter acetylenicus was grown in chemostat cocultures with either Acetobacterium woodii, Methanobacterium bryantii, or Desulfovibrio desulfuricans. Stable steady state conditions with tightly coupled growth were reached at various dilution rates between 0.02 and 0.14 h^-1. Both ethanol and H₂ steady state concentrations increased with growth rate and were lower in cocultures with the sulfate reducer < methanogen < homoacetogen. Due to the higher affinity for H₂, D. desulfuricans outcompeted M. bryantii, and this one A. woodii when inoculated in cocultures with P. acetylenicus. Cocultures with A. woodii had lower H₂ steady state concentrations when bicarbonate reduction was replaced by the energetically more favourable caffeate reduction. Similarly, cocultures with D. desulfuricans had lower H₂ concentrations with nitrate than with sulfate as electron acceptor. The Gibbs free energy (G) available to the H₂-producing P. acetylenicus was independent of growth rate and the H₂-utilizing partner, whereas the G available to the latter increased with growth rate and the energy yielding potential of the H₂ oxidation reaction. The critical Gibbs free energy (G_c), i.e. the minimum energy required for H₂ production and H₂ oxidation, was-5.5 to-8.0 kJ mol^-1 H₂ for P. acetylenicus,-5.1 to-6.3 kJ mol^-1 H₂ for A. woodii,-7.5 to-9.1 kJ mol^-1 H₂ for M. bryantii, and-10.3 to-12.3 kJ mol^-1 H₂ for D. desulfuricans. Obviously, the potentially available energy was used more efficiently by homoacetogens > methanogens > sulfate reducers.     

Alterations in synaptosomal neurotransmitter amino acids in “petit-mal” rats at a daytime and a nighttime

The synaptosoma fractions of 6 brain areas-olfactory tubercles (OT), frontal cortex (FC), striatum (Sr), amygdala (A), thalamus (Th), hypothalamus (Hy)-have been analyzed for their neurotransmitter amino acids (AA) content in Wistar rats exhibiting petit-mal epilepsy (PM-E) and in controls (C). The analysis was carried out at 11 p.m. (nighttime corresponding to the acrophase for the hourly number of spike-wave complexes) and at 11 a.m. (daytime). A day versus night rhythmicity is recorded for synaptosomal inhibitory AA in control and in PM-E rats. However, day versus night variations are more frequent and more prominent in C rats than in PM-E rats. Two day versus night variations exist only in PM-E rats: increases of GABA level in Sr and of Asp in Hy. Differences between PME-and C in synaptosomal AA content are more likely to be present during the nighttime. During this period lower AA values for PM-E rats are found for one or several inhibitory AA in OT, Th, and FC. It seems that the differences between PM-E and C concerning the inhibitory AA correlate with the number of spike-wave discharges. Only in one brain area is there a similar difference for PM-E and C during daytime and nighttime: a decreased GABA content for PM-E rats in OT. The decrease is larger in nighttime than in daytime. This difference may serve as a marker for this epileptic disorder. Moreover, it is in OT that the greatest number of PM-E versus C differences in synaptosomal neurotransmitter AA are observed. In view of these and former data, the existence of different alterations in synaptosomal neurotransmitter AA for different types of epilepsy is suggested.Abbreviations used GABA 4-aminobutyrate - Tau taurine - Gly glycine - Asp aspartate - Glu glutamate - Gln glutamine - OT offactory tubereles - FC fronto-parietal cortex - Sr striatum - A amygdala - Th lateral thalamus - Hy lateral hypothalamus - AA neurotransmitter amino acids - I inhibitory - E excitatory - C control rats - PM-E petit-mal rats