Purification and Characterization of Isocitrate Lyase from the Wood-Destroying Basidiomycete Fomitopsis palustris Grown on Glucose

Isocitrate lyase (EC 4.1.3.1), a key enzyme in the glyoxylate cycle, was purified 76-fold with 23% yield as an electrophoretically homogeneous protein from the wood-destroying basidiomycete Fomitopsis palustris grown on glucose. The native enzyme has a molecular mass of 186 kDa, consisting of three identical subunits of 60 kDa. The Km for dl-isocitrate was found to be 1.6 mM at the optimum pH (7.0). The enzyme required Mg2+ (Km 92 μM) and sulfhydryl compounds for optimal activity. The enzyme activity was strongly inhibited by oxalate and itaconate with a Ki of 37 and 68 μM, respectively. The inhibition by the glycolysis and tricarboxylic acid cycle intermediates and related compounds suggested that the isocitrate lyase was a regulatory enzyme playing a crucial role in the fungal growth.