Wg. Niehaus et Tc. Mallett, PURIFICATION AND CHARACTERIZATION OF GLUCOSE-6-PHOSPHATE-DEHYDROGENASE FROM CRYPTOCOCCUS-NEOFORMANS - IDENTIFICATION AS NOTHING DEHYDROGENASE, Archives of biochemistry and biophysics, 313(2), 1994, pp. 304-309
Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) was purified from Cryp
tococcus neoformans, a basidiomyceteous yeast that is an opportunistic
pathogen of AIDS patients. The enzyme had a subunit molecular weight
of 5 X 10(4), a specific activity of 50 units mg(-1), and K-m values f
or NADP and glucose-6-phosphate of 1.6 and 24 mu M, respectively. The
enzyme catalyzed the dehydrogenation of glucose, in the presence of di
methylsulfoxide, with K-m of 5 mM and V-max 10% of that with glucose-6
-phosphate. pH profiles indicated the presence of a group with pK(a) o
f 6.6 that is involved in catalysis, and groups with pK(a)s of about 8
.8 that are involved in binding of NADP and glucose-6-phosphate. The e
nzyme was inhibited by NADPH, competitive versus NADP, with K-i of 1 m
u M, and by zinc ion, competitive versus glucose-6-phosphate, with K-i
of 2 mu M. Crude enzyme extract catalyzed an appreciable rate of redu
ction of NADP in the absence of added substrate, a ''nothing dehydroge
nase'' activity. This activity was shown to be due to the presence of
glucose-6-phosphate in the crude extract. It was calculated that cells
of C. neoformans contain about 25 mu mol of glucose-6-phosphate per g
ram, wet weight. (C) 1994 Academic Press, Inc.