PURIFICATION AND CHARACTERIZATION OF MALATE-DEHYDROGENASE FROM CRYPTOCOCCUS-NEOFORMANS

The NAD-dependent malate dehydrogenase (EC 1.1.1.37) was purified from Cryptococcus neoformans, a basidiomycetious yeast that is an opportun istic pathogen of AIDS patients. The purified enzyme was a dimer of 35 kDa subunits that exhibited uncompetitive substrate inhibition by oxa lacetate, typical for mitochondrial malate dehydrogenases from other s ources. Product inhibition studies indicated an ordered sequential kin etic mechanism, with pyridine dinucleotide being the substrate that bi nds to the free enzyme form. Unique aspects of this malate dehydrogena se were inhibition by zinc ion, competitive versus malate with K-i of 30 mu M, and inhibition by heparin. Heparin inhibition was competitive versus either NAD or malate, with K-i of 0.35 mu M. Heparin molecules of nominal molecular weight of 30,000 or 3000 were equally effective inhibitors. A model is presented to explain the high affinity Of the e nzyme for heparin. (C) 1995 Academic Press, Inc.