Stereoconservative and stereoselective syntheses of rare and non-naturalα-amino acids from (S)-aspartic acid and (S)-malic acid

Summary A new strategy for stereoconservative and stereoselective syntheses of several types of amino acids starting from-functional carboxylic acids employing hexafluoroacetone as protecting and activating reagent is described. Outstanding features of this new method are the mild reaction conditions and the high yields for introduction and cleavage of the protective group allowing sensitive functional groups in the side chain to survive. Furthermore, the new concept results in saving of synthetic steps.     

Transglycosylating and hydrolytic activities of the β-mannosidase from Trichoderma reesei

A purified β-mannosidase (EC 3.2.1.25) from the fungus Trichoderma reesei has been identified as a member of glycoside hydrolase family 2 through mass spectrometry analysis of tryptic peptides. In addition to hydrolysis, the enzyme catalyzes substrate transglycosylation with p-nitrophenyl β-mannopyranoside. Structures of the major and minor products of this reaction were identified by NMR analysis as p-nitrophenyl mannobiosides and p-nitrophenyl mannotriosides containing β-(1 → 4) and β-(1 → 3) linkages. The rate of donor substrate hydrolysis increased in presence of acetonitrile and dimethylformamide, while transglycosylation was weakly suppressed by these organic solvents. Differential ultraviolet spectra of the protein indicate that a rearrangement of the hydrophobic environment of the active site following the addition of the organic solvents may be responsible for this hydrolytic activation.     

Yeast fungi in <Emphasis Type=Italic>Picea abies</Emphasis> (L.) Karst. needle litter

The amount of yeasts in spruce needle litter determined by plating onto needle infusion agar with penicillin can reach about 3 million cells/g, making up over a quarter of the whole micromycete population. During a 3-year survey, over 20 species belonging to nine genera were revealed, among which representatives of the genera Cryptococcus, Fellomyces, Rhodotorula, and Trichosporon were typical—specifically, Cr. carnescens, F. penicillatus, Rh. laryngis, and Tr. moniliiforme. The isolates showed lipase activity and were able to utilize hemicelluloses and phenolic compounds and secrete antifungal substances.     

Selenium Tolerance of Yeasts

Selenium tolerance of yeasts widely varies: the growth of some yeasts can be inhibited by a selenium concentration as low as 10^–4 M, whereas others can grow in the presence of 10^–1 M selenium. Homogeneous yeast taxa are characterized by a certain level of selenium tolerance, and heterogeneous taxa show a variable level of tolerance to selenium. In general, ascomycetous yeasts are more tolerant to selenium than basidiomycetous yeasts. Among the ascomycetous yeasts, the genera Dekkera and Schizosaccharomyces exhibited the lowest and the species Candida maltosa, Hanseniaspora valbyensis, Kluyveromyces marxianus, and Yarrowia lipolytica the highest tolerance to selenium. Among the basidiomycetous yeasts, the genera Bullera, Cryptococcusand Holtermannia showed the lowest and the species Cryptococcus curvatus, Cr. humicola, and Trichosporon spp. the highest tolerance to selenium. The selenium tolerance of yeasts depends on the composition of the growth medium, in particular, on the presence of sulfate, sulfur-containing amino acids, and glutamine in the medium.     

Assessment of the joint effect of thermal stress,pollution, and parasitic infestation on the activity of antioxidative enzymes in pulmonate mollusk <Emphasis Type="Italic">Lymnaea stagnalis</Emphasis>

This study makes a multifactor analysis of the joint effect of reservoir contamination, parasitic infestation, and experimental hyperthermia on the activity of antioxidative enzymes (peroxidase, catalase, and glutathione S-transferase) in the pulmonate mollusk Lymnaea stagnalis from the clean Naroch Lake and contaminated Chizhovsky Reservoir in the Republic of Belarus. The activity of peroxidase is ascertained to be affected most strongly by the simultaneous effect of parasitic infestation and reservoir contamination and parasitic infestation coupled with experimental hyperthermia. The joint effect of parasitic infestation and reservoir pollution is found to influence the activity of catalase. Meanwhile, no correlation is found between the studied factors and the activity of glutathione S-transferase. It is shown that there is no mutual influence of the three studied factors on the activity of the investigated enzymes.