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Inhibition of Ribulose Diphosphate Carboxylase by Cyanide

1969; Elsevier BV; Volume: 244; Issue: 1 Linguagem: Inglês

10.1016/s0021-9258(19)78190-3

1083-351X

Marcia Wishnick, M. Daniel Lane,

Polyamine Metabolism and Applications

Abstract Spinach leaf ribulose 1,5-diphosphate carboxylase is reversibly inhibited by cyanide at low concentration; 10-5 m and 10-4 m cyanide inhibit the carboxylation reaction 51% and 91%, respectively. Inhibition by cyanide (Ki = 1.6 x 10-5 m) is uncompetitive (anticompetitive) with respect to ribulose 1,5-diphosphate (ribulose-1,5-di-P) and is of mixed character with respect to Mg2+ and HCO3-. This and other kinetic evidence suggest that cyanide combines readily with enzyme-ribulose-1,5-di-P complex, but not with enzyme. The inference that enzyme-ribulose-1,5-di-P complex reacts with cyanide to form an inactive ternary complex is supported by binding studies with the use of the gel filtration technique. Ribulose-1,5-di-P uniformly labeled with 14C is tightly bound to the carboxylase (1.04 moles of ribulose-1,5-di-P per mole of enzyme) only in the presence of cyanide and 14C-cyanide is bound to the carboxylase (1.06 moles of cyanide per mole of enzyme) only in the presence of ribulose-1,5-di-P. The presence of Mg2+ is without effect on 14C-ribulose-1,5-di-P binding in the presence of cyanide or on 14C-cyanide binding in the presence of ribulose-1,5-di-P under the conditions used. A ternary complex of ribulose-1,5-di-P carboxylase, ribulose-1,5-di-P, and cyanide in a mole ratio of 1:1:1 is indicated. Attempts to demonstrate Schiff base formation between the carboxylase and ribulose-1,5-di-P under a wide variety of conditions were unsuccessful.