Niehaus W G, Mallett T C
Department of Biochemistry and Anaerobic Microbiology, Virginia Polytechnic Institute and State University, Blacksburg 24061-0308.
Arch Biochem Biophys. 1994 Sep;313(2):304-9. doi: 10.1006/abbi.1994.1392.
Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) was purified from Cryptococcus 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 Km values for NADP and glucose-6-phosphate of 1.6 and 24 microM, respectively. The enzyme catalyzed the dehydrogenation of glucose, in the presence of dimethylsulfoxide, with Km of 5 mM and Vmax 10% of that with glucose-6-phosphate. pH profiles indicated the presence of a group with pKa of 6.6 that is involved in catalysis, and groups with pKas of about 8.8 that are involved in binding of NADP and glucose-6-phosphate. The enzyme was inhibited by NADPH, competitive versus NADP, with Ki of 1 microM, and by zinc ion, competitive versus glucose-6-phosphate, with Ki of 2 microM. Crude enzyme extract catalyzed an appreciable rate of reduction of NADP in the absence of added substrate, a "nothing dehydrogenase" 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 mumol of glucose-6-phosphate per gram, wet weight.
葡萄糖-6-磷酸脱氢酶（EC 1.1.1.49）是从新型隐球菌中纯化得到的，新型隐球菌是一种担子菌酵母，也是艾滋病患者的机会致病菌。该酶的亚基分子量为5×10⁴，比活性为50单位mg⁻¹，对NADP和葡萄糖-6-磷酸的Km值分别为1.6和24μM。在二甲基亚砜存在下，该酶催化葡萄糖脱氢，Km为5 mM，Vmax为以葡萄糖-6-磷酸为底物时的10%。pH曲线表明存在一个pKa为6.6的参与催化的基团，以及pKa约为8.8的参与NADP和葡萄糖-6-磷酸结合的基团。该酶受到NADPH的抑制，对NADP呈竞争性抑制，Ki为1μM，也受到锌离子的抑制，对葡萄糖-6-磷酸呈竞争性抑制，Ki为2μM。粗酶提取物在没有添加底物的情况下催化NADP有明显的还原速率，即“无底物脱氢酶”活性。已证明这种活性是由于粗提取物中存在葡萄糖-6-磷酸。据计算，每克湿重的新型隐球菌细胞含有约25μmol的葡萄糖-6-磷酸。
