Stereoselectivity

Preliminary experiments shows, that [3+2] cycloadditions reactions proceeds with full regioselectivity and high stereoselectivity. In consequence, 3,4-trans-2-methyl-3-(3,4,5-trimethoxyphenyl)-4-halo-4-nitroisoxazolidines are forming as predominantly (or sole) products. Additionally, prognosis for the synthesized compounds to be potential ingredients of drugs is good.

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We have determined the nucleotide sequence of a DNA fragment covering the flanking region of the R-stereoselective amidase gene, ramA, from the Pseudomonassp. MCI3434 genome and found an additional gene, bapA, coding for a protein showing sequence similarity to DmpA aminopeptidase from Ochrobactrum anthropiLMG7991 (43% identity).

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NAD + -dependent (R)-2-hydroxyglutarate dehydrogenase (HGDH) cata-lyses the reduction of 2-oxoglutarate to (R)-2-hydroxyglutarate and belongs to the D-2-hydroxyacid NAD + -dependent dehydrogenase (D-2-hydroxyacid dehydrogenase) protein family. Its crystal structure was determined by phase combination to 1.98 A˚ resolution. Structure–function relationships obtained by the comparison of HGDH with other members of theD-2-hydroxyacid dehydrogenase family give a chemically satisfying view of the substrate stereoselectivity and catalytic requirements for the hydride trans-fer reaction.

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Kinetic experiments with a substrate series of phenylacetyl-arylamides reveal that at least one polar group in the amine moiety is required for the proper orientation of the substrate in the large nucleophile-binding subsite of penicillin acylase ofEscherichia coli. Quantum mechanical molecular model-ling of enzyme–substrate interactions in the enzyme active site shows that in the case of substrates lacking local sym-metry, the productive binding implies two nonsymmetrical arrangements with respect to the two positively charged guanidinium residues of ArgA145 and ArgB263....

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A novel amidase acting on (R,S)-piperazine-2-tert-butyl-carboxamide was purified fromPseudomonassp. MCI3434 and characterized. The enzyme acted R-stereoselectively on (R,S)-piperazine-2-tert-butylcarboxamide to yield (R)-piperazine-2-carboxylic acid, and was tentatively named R-amidase. The N-terminal amino acid sequence of the enzyme showed high sequence identity with that deduced from a gene named PA3598 encoding a hypothetical hydrolase in Pseudomonas aeruginosaPAO1.

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An amidase acting on (R,S)-piperazine-2-tert-butylcarbox-amide was purified fromPseudomonas azotoformansIAM 1603 and characterized. The enzyme actedS-stereoselec-tively on (R,S)-piperazine-2-tert-butylcarboxamide to yield (S)-piperazine-2-carboxylic acid. N-terminal and internal amino acid sequences of the enzyme were determined. ThegeneencodingtheS-stereoselective piperazine-2-tert-butylcarboxamide amidase was cloned from the chromo-somal DNAof the strain and sequenced.

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We addressed the ability of various organophosphorus (OP) hydrolases to catalytically scavenge toxic OP nerve agents. Mammalian paraoxonase (PON1) was found to be more active than Pseudomonas diminutaOP hydrolase (OPH) and squidO,O-di-isopropyl fluorophosphatase (DFPase) in detoxifying cyclosarin (O-cyclohexyl methylphosphonofluoridate) and soman (O-pinacolyl methylphosphonofluoridate).

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The effect of pH and temperature on structure, stability, activity and enantioselectivity of haloalkane dehalogenase DbjA from Bradyrhizobium japonicum USDA110 was investigated in this study. Conformational changes have been assessed by circular dichroism spectroscopy, functional changes by kinetic analysis, while quaternary structure was studied by gel filtration chromatography.

11p cosis54 05-01-2013 56 4   Download