Purification and some properties of 6-phosphoglucose isomerase from Bacillus caldotenax

6-Phosphoglucose isomerase [EC 5.3.1.9] was purified from Bacillus caldotenax. The isomerase shared many common properties with the isomerase from B. stearothermophilus, i.e, pH and temperature optima, thermostability, competitive inhibition by 6-phosphogluconate and Pi, and amino acid composition. The enzyme activity of the former, however, was lower than that of the latter. The molecular weight of the B. caldotenax isomerase was estimated to be 202,000-204,000 by gel filtration and electrophoresis of the enzyme cross-linked with dimethyl adipimidate (DMA). The enzyme was shown to consist of four subunits of equal molecular weight (50,600), and the four subunits were concluded to be identical based on the results of dansylation and cyanogen bromide cleavage of the enzyme. The interaction between the subunits were shown to be isologous by cross-linking with DMA.