title: Stereochemical course of the generation of 3-mercaptohexanal and 3-mercaptohexanol by beta-lyase-catalyzed cleavage of cysteine conjugates.
abstract: The product resulting from the reaction between E-2-hexenal and l-cysteine was shown to be a diastereoisomeric mixture of 2-(2-S-l-cysteinylpentyl)-1,3-thiazolidine-4-carboxylic acid 1. Treatment of the conjugate with two sources of cysteine-S-conjugate beta-lyase (tryptophanase from E. coli and a crude enzyme extract prepared from Eubacterium limosum) resulted in the formation of 3-mercaptohexanal. The reaction proceeded with a slight preference for the (S)-configured product, however, with low conversion rate. The role of 3-S-l-cysteinylhexanal 2 as substrate for beta-lyases was demonstrated by in situ generation of 2 from 3-S-(N-acetyl-l-cysteinyl)hexanal using acylase. Opposite enantioselectivity was observed for the liberation of 3-mercaptohexanol from 3-S-l-cysteinylhexanol 5 by the enzyme preparations from Eubacterium limosum and tryptophanase. Various yeasts produced 3-mercaptohexanol starting from 1 as well as from 5. The reactions proceeded without preferential formation of one of the enantiomers.
authors.affiliation: Lehrstuhl für Allgemeine Lebensmitteltechnologie, Technische Universität München, Am Forum 2, D-85350 Freising-Weihenstephan, Germany.
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Wakabayashi
authors.forename: Motoko
authors.initials: M
authors.lastname: Wakabayashi
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eisenreich
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Engel
mesh_terms: D000447:Aldehydes / Q000378:metabolism*; D013437:Carbon-Sulfur Lyases / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology; D005051:Eubacterium / Q000201:enzymology; D008401:Gas Chromatography-Mass Spectrometry; D000441:Hexanols / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000378:metabolism*
chemical_list: D000447:Aldehydes; D000441:Hexanols; D013438:Sulfhydryl Compounds; C477018:3-mercaptohexanal; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase; D003545:Cysteine; C477019:3-mercaptohexanol