Yag. Mahmoud et al., PURIFICATION AND CHARACTERIZATION OF MALATE-DEHYDROGENASE FROM CRYPTOCOCCUS-NEOFORMANS, Archives of biochemistry and biophysics, 322(1), 1995, pp. 69-75
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.