Specificity of the reaction of rat liver L-serine dehydratase with aminothiols

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Abstract
The degree, mechanism and specificity of the inhibition of purified rat liver L-serine dehydratase by L-cysteine and aminothiols were investigated. All the aminothiols tested, react with free pyridoxal-5''-phosphate (PLP); only L-cysteine reacts with PLP bound to the enzyme, giving an absorption spectrum similar to that of the thiazolidinic ring formed in the chemical reaction. The reaction between L-cysteine and PLP bound to the enzyme has a particular behavior, different from all the other aminothiols. A stereospecific interaction between L-cysteine and PLP bound to the enzyme, forming one of the 2 possible diastereoisomers, is postulated.