Purification and Characterization of Malate Synthase from the Glucose-grown Wood-rotting Basidiomycete Fomitopsis palustris

Abstract

  Malate synthase (EC 4.1.3.2), the key enzyme of the glyoxylate cycle, was purified to a homogeneous protein from the wood-rotting basidiomycete Fomitopsis palustris grown on glucose. The purified enzyme, with a molecular mass of 520 kDa, was found to consist of eight 65-kDa subunits, and to have K_m of 45 and 2.2 μM for glyoxylate and acetyl-CoA, respectively. The enzyme activity was competitively inhibited by oxalate (K_i, 8.5 μM) and glycolate (K_i, 17 μM), and uncompetitively by coenzyme A (K_i, 100 μM). The potent inhibition of the activity by p-chloromercuribenzoate suggests that the enzyme has a sulfhydryl group at the active center. However, the enzyme was inhibited moderately by adenine nucleotides and weakly by some of the metabolic intermediates of glycolysis and tricarboxylic acid cycle. The enzyme was completely inactive in the absence of metal ions and was maximally activated by Mg²⁺ (K_m, 0.4 μM), which also served to significantly prevent enzyme inactivation during storage.