Regulatory properties of 6-phosphogluconate dehydrogenase from higher plants

1. 1. 6-Phosphogluconate dehydrogenase (6PGDH, E.C.I.1.1.44) was extracted from hypocotyls of black gram seedlings and phloem of carrot roots and partially purified by fractionation with ammonium sulfate. 2. 2. 6PGDH from both sources showed hyperbolic kinetics for 6-phosphogluconate (6PG) and NADP + . 3. 3. Activity of 6PGDH was competitively inhibited by NADPH, ATP, and 5-phosphoribosyl-1-pyrophosphate. 4. 4. Mg 2+ and Mn 2+ activated the enzyme activity. 5. 5. ATP inhibition was reversed by Mg 2+ or at relatively high pH (7.6–8.0). 6. 6. Fructose-1,6-diphosphate, ADP, AMP, and citrate, inhibitors of mammalian 6PGDH, had little or no effect on the plant enzyme. 7. 7. The possible function of the properties of 6PGDH in the regulation of the pentose phosphate pathway in plants is discussed.