ISOLATION OF 2-METHYLISOCITRATE DEHYDRATASE, A NEW ENZYME SERVING IN THE METHYLCITRIC ACID CYCLE FOR PROPIONATE METABOLISM, FROM YALLOWIA-LIPOLYTICA

2-Methylisocitrate dehydratase (EC 4.2.1.-; (2S,3R)-3-hydroxybutane-1,2,3-tricarboxylate hydrolyase), a new enzyme functioning in the methylcitric acid cycle of propionate metabolism, was found in cells of Yallowia lipolytica, separated from the usual aconitase (EC 4.2.1.3), and purified about 120-fold to homogeneity as judged electrophoretically. The new enzyme catalyzed a reversible reaction between 2-methylisocitrate and 2-methyl-cis-aconitate, but was inactive toward 2-methylcitrate, citrate, cis- or trans-aconitate, isocitrate, or the other hydroxy-acids tested, Equilibrium was reached at about 92% of 2-methylisocitrate, with the rest as 2-methyl-cis-aconitate. The isolated aconitase also catalyzed the reversible reaction and its K-m for 2-methylisocitrate was 120 mu M, but that of the new enzyme was 18 mu M.