Regulation of Ribulose 1,5-Diphosphate Carboxylase by Substrates and Other Metabolites

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Abstract
Ribulose 1,5-diphosphate carboxylase (RuDPCase, EC 4.1.1.39) isolated from spinach leaves is metabolically regulated at 10 mm Mg2+ and low CO2 concentrations by its substrates (RuDP and CO2) and by effectors which include 6-phosphogluconate (6-PGluA), NADPH, and fructose 1,6-diphosphate (FDP), but not fructose 6-phosphate. Physiological concentrations of RuDP severely inhibit the enzyme activity when the enzyme has not been preincubated with HCO3− and Mg2−, and this inactivity persists for 20 minutes or longer after 1 mm HCO3− and 10 mm Mg2+ are added. Maximum activity requires that the preincubation mixture also include either 0.01 mm 6-PGluA or 0.5 mm NADPH.
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