Enhancing a Sphaerobacter thermophilus ω-transaminase for kinetic resolution of β- and γ-amino acids.

Sphaerobacter thermophilus synthesizes an ω-transaminase (ω-TA) that allows the production of enantiomerically pure β-amino acids. To obtain ω-TA variants with a higher activity and more favorable properties for industrial use, we modified critical amino acid residues either in the catalytic center or in a previously proposed signature motif critical for aromatic β-amino acid ω-TAs. Seventeen different variants of this enzyme were generated and their activity was examined with four β-amino acids and one γ-amino acid, and compared with the wildtype's activity.

Coexpression of Lactobacillus brevis ADH with GDH or G6PDH in Arxula adeninivorans for the synthesis of 1-(R)-phenylethanol.

The yeast Arxula adeninivorans was used for the overexpression of an ADH gene of Lactobacillus brevis coding for (R)-specific alcohol dehydrogenase (LbADH) to synthesise enantiomerically pure 1-(R)-phenylethanol. Glucose dehydrogenase gene from Bacillus megaterium (BmGDH) or glucose 6-phosphate dehydrogenase of Bacillus pumilus (BpG6PDH) were coexpressed in Arxula to regenerate the cofactor NADPH by oxidising glucose or glucose 6-phosphate. The yeast strain expressing LbADH and BpG6PDH produced 5200 U l(-1) ADH and 370 U l(-1) G6PDH activity, whereas the strain expressing LbADH and BmGDH produced 2700 U l(-1) ADH and 170 U l(-1) GDH activity.

Microbial degradation of 2 alpha, 3 alpha-dihydroxy-5 alpha-cholestan-6-one by Mycobacterium vaccae.

2 alpha,3 alpha-Dihydroxy-5 alpha-cholestan-6-one (3), which had the substitution pattern of brassinosteroids in the A/B-ring moiety, was transformed by Mycobacterium vaccae to give 2 alpha,3 alpha,6 alpha-trihydroxy-5 alpha-androstan-17-one (4) and 2 alpha-hydroxyandrost-4-ene-3,17-dione (5). The structures of these compounds were determined by spectroscopic methods, especially 1H nuclear magnetic resonance studies.

Effects of (22S,23S)-Homobrassinolide and Related Compounds on Membrane Potential and Transport of Egeria Leaf Cells.

(22S,23S)-Homobrassinolide was tested for its effect on the electric cell potential, proton extrusion, ferricyanide reduction, and amino acid and sucrose uptake of leaves of Egeria densa Planchon. In the light, (22S,23S)-homobrassinolide and its derivative, 2alpha-3alpha-dihydroxy-5alpha-stigmast-22-en-6-one, were similar to each other and similar to fusicoccin in causing hyperpolarization and proton extrusion, whereas stigmasterol was less effective. In darkness, the three sterols showed comparable effects.