Pigeon Liver Malic Enzyme

Abstract

Abstract Pigeon liver malic enzyme (malate dehydrogenase (decarboxylating), EC 1.1.1.38) was purified and crystallized from ammonium sulfate solution as its triphosphopyridine nucleotide complex. The crystalline protein is homogeneous in the ultracentrifuge, in gradient centrifugation, and in gradient chromatography. A constant specific activity of 28 units per mg of protein is obtained. The crystalline enzyme has an s20 of 10.0, an apparent diffusion coefficient of 3.17 x 10-7 cm2 per sec, and an apparent partial specific volume of 0.74. Its molecular weight is 2.8 x 105. Purified malic enzyme has an ultraviolet absorption maximum at 278 mµ. The extinction coefficients for the purified enzyme and the crystalline TPN complex are 0.86 and 0.92, respectively, for a 0.10% protein solution. The purified enzyme catalyzes the decarboxylation of oxalacetate at a rate comparable to the decarboxylation of malate. Reversible inactivation of these activities occurs upon storage of the enzyme. Reactivation is obtained by incubation with dithiothreitol.