L-METHIONINE-GAMMA-LYASE IN CITROBACTER-INTERMEDIUS CELLS - STEREOCHEMICAL REQUIREMENTS WITH RESPECT TO THE THIOL STRUCTURE

The specificity of L-methionine-gamma-lyase with respect to the stereo chemical structure of the thiol substrate in the gamma-substitution re action has been demonstrated. Cells of Citrobacter intermedius contain ing L-methionine-gamma-lyase catalyze the exchange reactions between L -methionine and 2-propylthiol or 2-butylthiol which leads to the forma tion of s-2-propylhomocysteine and s-2-butylhomocysteine, respectively . The yields of these products are comparable to the yield of s-butylh omocysteine in the reaction of normal butylthiol with L-methionine, th us 2-propylthiol and 2-butylthiol are effective substrates of L-methio nine-gamma-lyase. On the other hand in the reaction of 3-pentylthiol, only traces of the expected product, s-3-pentylhomocysteine, were form ed and in the case of 2-methyl-2-butylthiol, the expected product of g amma-substitution, s-2-methyl-2-butylhomocysteine, was not formed at a ll. In the reaction with racemic 2-butylthiol, only one diastereomer o f s-2-butylhomocysteine was obtained. The unreacted 2-butylthiol isola ted after the reaction catalyzed by partially purified preparation of L-methionine-gamma-lyase was enriched with (R)-enantiomer which indica ted the preferential reaction of the (S)-enantiomer. (C) 1996 by Elsev ier Science Inc.