Purification and properties of glucose-6-phosphate dehydrogenase from Bacillus stearothermophilus

Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP+ 1-oxidoreductase, EC 1.1.1.49) from the thermophilic bacteria, Bacillus stearothermophilus, was purified and its properties were examined. The enzyme was shown to consist of four identical subunits, each of about Mr 50,000. This enzyme utilized both NADP+ and NAD+ as cofactors, and the maximum velocity for both cofactors was similar. However, the Km values were quite different from each other, being 0.016 and 1.64 mM for NADP+ and NAD+, respectively. From the analysis of sulfhydryl groups it was shown that there is one sulfhydryl group and one disulfide bridge per subunit. This sulfhydryl group had no reactivity with 5,5'-dithiobis(2-nitrobenzoic acid) in the absence of guanidine hydrochloride. The enzyme showed a remarkable thermostability as well as storage stability.