Evidence for two distinct CoA binding sites on yeast alpha-isopropylmalate synthase.

cu-Isopropylmalatesynthase (EC 4.1.3.12) from Saccharomyces cerevisiae was purified to a purity of about 95%.The molecular weight of the enzyme is approximately 127,000, as determined by sedimentation equilibrium centrifugation and by intersubunit cross-linking.Under denaturing conditions, one major species (95%) with molecular weight of about 65,000 is obtained.The dimeric structure of the enzyme is apparently unaffected by the presence of various ligands, including substrates, the feedback inhibitor leutine, and the inactivating combination of CoA plus Zn"+.Our previous observation that CoA, a product of the reaction, causes a very specific, Zn2+-dependent, reversible inactivation of yeast a-isopropylmalate synthase (Tracy, J., and Kohlhaw, G. B. (