Purification and Characterization of 6-Phosphogluconate Dehydrogenase from Phormidium sp.

the native enzyme was 104,000 by gel filtration, and SDS-polyacrylamide gel electrophoresis showed that the enzyme consisted of two subunits with an identical molecular weight of 52,000. The optimum pH of the reaction was 8.0. The Km values for 6-phosphogluconate and NADP were 3.6×10^?5m and 1.3 × 10^?5m, respectively. The enzyme showed no Mg^2𠀫 requirement for the activity, but was activated by Mn^2𠀫 and Ca^2𠀫. The enzyme was inhibited by sulfhydryl reagents, indicating that a sulfhydryl group may be involved in the active site of the enzyme. The enzyme was also inhibited by NADPH₂, ATP, and the intermediates formed during photosynthesis. The substrate 6-phosphogluconate and cofactor NADP partially protected the enzyme from inactivation. The enzyme had enzymological and physicochemical properties similar to enzymes isolated from other sources.