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B6db references: ubbabaluuba

type Journal Article
authors Mazelis, M,; Scott, K.; Gallie, D.
title Non-identity of cystine lyase with β-cystathionase in turnip roots
journal Phytochemistry
Activity cystine.lyase
sel unselected
ui ubbabaluuba
year (1982)
volume 21
number 5
pages 991-995
 
abstract An active preparation of cystine lyase (EC 4.4.1.-) was prepared from turnip roots and its substrate specificity examined. Only Image -cysteine, cysteine-S-SO3, and the sulphoxides of Image -djenkolic acid, S-methyl-and S-ethyl-Image -cysteine were substrates. Image -Cystathione, Image -djenkolic acid, S-methyl-and S-ethyl-cysteines were not cleaved by this enzyme. The Km for Image -cystine was 1.3 mM and Image -cystathionine acted as an effective competitive inhibitor with a Ki of 0.7 mM. After dialysis against 10 mM potassium phosphate buffer pH 7.5, added pyridoxal phosphate was absolutely necessary for activity. In addition a marked stimulation was observed in the presence of ammonium sulphate. The products of the reaction were cysteine persulphide, pyruvate and presumably ammonia. The persulphide was easily demonstrated by cleavage with CN− to yield SCN− under conditions in which elemental sulphur was unreactive.
last changed 2008/05/21 18:37

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