SULFHYDRYL GROUPS OF CITRATE CLEAVAGE ENZYME

Chicken liver citrate cleavage enzyme has an apparent optimum activity at pH 8.7, similar to the enzyme isolated from rat liver. Early results indicating a lower pH optimum were due to a pH dependent disulfide inhibition of the enzyme. Both chicken liver and rat liver citrate cleavage enzymes are inhibited by oxidized glutathione, oxidized BAL, lipoate, and arsenite. Studies with the purified rat liver enzyme indicate the presence of 6-8 moles of very reactive SH groups per mole of enzyme which are essential for enzyme activity. These groups can be protected by Mg-citrate but not by Mg-ATP. The loss of enzyme activity observed upon storage and its subsequent reactivation by dithiothreitol does not result from changes in aggregation and dissociation of the enzyme as judged by gel electrophoresis and ultracentrifugation. © 1969.