6-Phosphogluconate dehydrogenase in cell free extracts of Escherichia coli K-12

Summary Investigations into the properties of 6-PG dehydrogenase in cell free extracts of Escherichia coli revealed a pH optimum at pH 9.5 with a sharp decline on both sides of the optimum. The addition of 1.0×10^-2m MgCl₂ produced maximal activity, whereas higher concentrations caused inhibition. The K_m values were 2.5×10^-4m for 6-phosphogluconate and 2.5×10^-5m for NADP⁺ as substrate. The enzyme was extremely stable for at least 5 hours if stored at 4°C in Tris–NaCl–MgCl₂ buffer at pH 7.5. 6-PG dehydrogenase activity was shown to be proportional to cell free extract concentration over the range 0–0.3 mg protein. An assay method based on the new optimal conditions has been established and has been shown to be 33% more sensitive than a number of commonly used methods.Meinem hochverehrten Lehrer Herrn Professor A. Rippel zum 80. Geburtstage.