Role of O-acetylhomoserine sulfhydrylase in sulfur amino acid synthesis in various yeasts

Mutants defective in O-acetylhomoserine sulfhydrylase (OAH-SHLase) were obtained in five yeast strains representative of different yeast genera: Saccharomyces cerevisiae, Kluyveromyces lactis, Yarrowia lipolytica, Schizosaccharomyces pombe and Trichosporon cutaneum. In vitro, in all five strains, the enzyme also had O-acetylserine (OAS) sulfhydrylase activity so it is a ‘bifunctional’ OAH/OAS-SHLase (Yamagata, 1989). The enzyme was only found to be essential in S. cerevisiae (OAH SHLase-negative mutants are auxotrophs). Its impairment in K. lactis caused a slower growth rate and a decrease of the sulfur amino acid pool. In T. cutaneum only the pool was affected whereas in Y. lipolytica and S. pombe the lesion caused no change in the growth rate nor in the pool. In all strains where OAH SHLase-negative mutants were prototrophs, a monofunctional OAS sulfhydrylase was detected. The results indicate that OAH SHLase may play different physiological roles in various yeasts.     

Determination of the glass transition temperature of poly(styrene-co-divinylbenzene) by inverse gas chromatography

Inverse gas chromatography (i.g.c.) was used to characterize the supermolecular structure of modified, moderately crosslinked poly(styrene-co-divinylbenzene) (5–20 wt%) and to determine the interactions with normal alcohols (C₁C₆). For all copolymers a decrease of retention time with increasing molecular weight of alcohols from C₁ to C₃ followed by an increase for C₄ to C₆ alcohols was observed. It was found that with propanol or butanol the measured T_g values were close to those measured by d.s.c. The T_g values for poly(styrene-co-divinylbenzene) containing 5, 10 and 20 wt% divinylbenzene were: 102°C, 116°C and 133°C respectively. The highest alcohols (C₅ and C₆) acted as plasticizers and reduced the apparent T_g value. The relationship between the isosteric heat of adsorption and the number of carbon atoms in the alcohols was nonlinear with a minimum corresponding to butanol.     

Client-specific A-stack model for adult face verification across aging

The problem of time validity of biometric models has received only a marginal attention from researchers. In this paper, we propose to manage the aging influence on the adult face verification system by an A-stack age modeling technique, which uses the age as a class-independent metadata quality measure together with scores from a single or multiple baseline classifiers, in order to obtain better face verification performance. This allows for improved long-term class separation by introducing a dynamically changing decision boundary across the age progression in the scores-age space using a short-term enrollment model. This new method, based on the concept of classifier stacking and age-aware decision boundary, compares favorably with the conventional face verification approach, which uses age-independent decision threshold calculated only in the score space at the time of enrollment. Our experiments on the YouTube and MORPH data show that the use of the proposed approach allows for improving the identification accuracy as opposed to the baseline classifier.     

The influence of pH on the thermal stability of 5-<Emphasis Type="Italic">O</Emphasis>-caffeoylquinic acids in aqueous solutions

Chlorogenic acid, the ester of caffeic acid with quinic acid, is a natural phenolic compound found in all higher plants. It is potentially useful in pharmaceuticals, foodstuffs, feed additives, and cosmetics due to recently discovered biomedical activity of this compound. This finding caused new interest in the properties of chlorogenic acid in its isomers and in its natural occurrence. It has been found that as many as fourteen compounds (chlorogenic acid derivatives and its reaction products with water) can be formed from 5-O-caffeoylquinic acid by heating its water solution at different pH. Four of them, two hydroxylated 3-O-caffeoylquinic acid derivatives and two hydroxylated 4-O-caffeoylquinic acid derivatives, have been not reported yet. The amount of each formed component depends on the heating time and pH. The transformation product can be mistakenly treated as a new component, not found before in the examined plant, or can be a cause of erroneous quantitative estimations of plant composition.     

Application of electron paramagnetic resonance (EPR) spectroscopy for control of irradiated food

Four groups of foodstuffs were irradiated in a ⁶⁰Co source with doses from 0.3 to 10kGy and subsequently measured by EPR spectrometry at room temperature in air: (1) poultry bones and fins, scales and bones of carp. (2) seeds of selected fruits, (3) dehydrated mushrooms, and (4) a selected set of spices and herbs. Qualitative and, in some cases, quantitative data related to the absorbed dose of radiation were collected. In the irradiated bones from poultry and carp an asymmetric singlet (g_I = 2.0030, g_II =1.9973; ΔH_pp = 0.85 mT) was detected which was stable at room temperature and was similar to that previously found in irradiated mammalian bones. Another stable EPR signal (g₀ = 2.0024, ΔH_pp = 0.56 mT) was found in the fins and scales of carp which was about five times more intense in fins than in scales. In pips of pears irradiated with a dose of 3 kGy. a signal which was about twice as intense as the endogenous signal was recorded. A multicomponent EPR signal derived from the stones of dates differed from the endogenous signal even when a low dose (0-5 kGy) was applied. A multicomponent EPR signal is also observed in dried mushrooms irradiated with a dose of 3 kGy. In white mustard, paprika and chilli no native EPR signal exists and a radiation-induced stable EPR signal can still be observed after a period of 3 months. The radiation-induced EPR signal in black pepper was highly sensitive to moisture and disappeared, yet the native signal survived. The pilot experiments performed with irradiated stones of cherries, plums, lemons, apple pips, raspberries, cranberries, red currants, blackcurrants, gooseberries and tomatoes showed the induction of short-lived EPR signals of no practical use for the control of food irradiation.     

A Basic Theoretical Model for Friction Process at Microasperity Level

This article presents a theoretical model for dry, low-velocity, and wear-less friction based on a single asperity interaction with arbitrary assumed adhesion forces and elastic deformations of the microasperities. Simulations of friction behavior according to the single asperity interaction, as well as the interaction of multiplied single models, are presented. The multiplied model assumes a regular distribution of the single asperities, arbitrarily chosen geometrical properties (based on harmonic function), and elastomechanical properties of the cooperating materials. In the proposed model, the adhesion as a function of asperity deformation is introduced. This enables the simulation of an expedient local coefficient of friction. The model assumes no breaking of the contact between single asperities; however, the proposed model enables detection of such a situation. The results obtained by simulation of the model show both qualitative and quantitative agreement with the known types of friction force dynamic behavior, in particular, nonlinearity of the friction coefficient. At this level of investigation, the model assumes the most important relations connected with its properties, which need further refinement and elaboration, especially according to assumed asperity properties.     

The hildebrand solubility parameters of ionic liquids-part 2

The Hildebrand solubility parameters have been calculated for eight ionic liquids. Retention data from the inverse gas chromatography measurements of the activity coefficients at infinite dilution were used for the calculation. From the solubility parameters, the enthalpies of vaporization of ionic liquids were estimated. Results are compared with solubility parameters estimated by different methods.     

Silane–parylene coating for improving corrosion resistance of stainless steel 316L implant material

The corrosion resistance of a two-layer polymer (silane + parylene) coating, on implant stainless steel was investigated by microscopic observations and electrochemical measurements. Long term exposure tests in Hanks solution revealed that the coating of 2 μm can be successfully used for corrosion protection. However, the addition of H₂O₂, simulating the inflammatory response of human body environment causes a dramatic destruction of the protective coating. Analysis of the experimental data in terms of circuit models enables proposing a deterioration mechanism. OH radicals formed at the metal surface attack the polymer, thus the deterioration starts from the metal/polymer interface and progress towards the outward surface.     

New Non Phyto‐ and Eco‐Toxic Alumina‐Stabilized Silver and Praseodymium Nanoparticles

In the present study, we examined how the active aluminum nano‐oxide in the gamma form used as a neutral carrier for the nanoparticles of various metals (as Ag, Pr) affected their toxic behavior. Our experiments have shown that exposure to metal nanoparticles can be reduced by binding the nanoparticles to alumina nanoparticles and the aluminum nano‐oxide is suitable to function as the nano‐stabilizer for the Ag and Pr nanoparticles. We have managed to manufacture new alumina‐stabilized silver and praseodymium nanoparticles using dry sol‐gel method that are not phyto‐ and eco‐toxic.