Retno Indrati

β-Carbon stereoselectivity of N-carbamoyl-d-α-amino acid amidohydrolase for α,β-diastereomeric amino acids

N-Carbamoyl-d-α-amino acid amidohydrolase (d-carbamoylase) was found to distinguish stereochemistry not only at the α-carbon but also at the β-carbon of N-carbamoyl-d-α-amino acids. The enzyme selectively acted on one of the four stereoisomers of N-carbamoyl-α,β-diastereomeric amino acids. This simultaneous recognition of two chiral centers by d-carbamoylase was useful for the fine stereoselective synthesis of α,β-diastereomeric amino acids such as threonine, isoleucine, 3,4-methylenedioxyphenylserine and β-methylphenylalanine. The stereoselectivity for the β-carbon was influenced by the pH of the reaction mixture and by the bulk of the substituent at the β-carbon.

Simultaneous recognition of two chiral centers in α,β-diastereomeric amino acids by an N-carbamoyl-L-α-amino acid amidohydrolase from Alcaligenes xylosoxidans

Cells of Alcaligenes xylosoxidans containing N-carbamoyl-L-α-amino acid amidohydrolase strictly distinguished the configuration of not only the α-carbon but also the β-carbon of N-carbamoyl-β-methylphenylalanine, and produced threo-l-β-methylphenylalanine specifically from a mixture of the four stereoisomers.

Pengaruh Konsentrasi Xilosa dan Kosubstrat Terhadap Produksi Xilitol oleh Candida shehatae Way 08

The objectives of the research were to determine the optimum cultivation condition of initial xylose concentration, type of cosubstrate and ratio of cosubstrate to substrate (xylose) for xylitol production by Candida shehatae WAY 08. The initial xylose concentrations were varied within the range of 2-14 %. The cosubstrates were arabinose, galactose, glucose, and mannose. Ratios of cosubstrate to xylose were the range of 1:6 - 3:6 %. The fermentation was performed at 30`C in a 500 ml Erlenmeyer flask placed in a shaker incubator at 200 rpm for 72 h. Biomass concentration was determined by drying method. Xylose, cosubstrate and xylitol concentrations were determined using HPLC. The result indicated that with the medium containing 6 % xylose produced the highest product yield ( 0,75 g/g) and xylitol volumetric productivity was 0,73 g/Lh. The addition of cosubstrate of arabinose increased xylitol production, while the addition of glucose, galactose, and mannose decreased its productions.