Specific inhibition of oxygenase activity of ribulose-1,5-diphosphate carboxylase by hydroxylamine

Ribulose-1,5-diphosphate oxygenase activity of ribulose-1,5-diphosphate carboxylase was completely inhibited by preincubation of the enzyme with 5mM hydroxylamine in presence of the substrate ribulose-1,5-diphosphate. Inhibition by hydroxylamine was uncompetitive with respect to ribulose-1,5-diphosphate and noncompetitive with respect to magnesium. Carboxylase activity was not affected by hydroxylamine. These results suggest that the two activities of the enzyme can be regulated differentially and that inhibiting the oxygenase activity does not stimulate the carboxylase activity of the enzyme. The data further suggest that the inhibition by hydroxylamine may be through its interaction with carbonyl groups of the enzyme exposed on the binding of ribulose-1,5-diphosphate to the protein.