Inhibition of Ribulose Diphosphate Carboxylase by Cyanide

• Published in: The Journal of biological chemistry Vol. 244; no. 1; pp. 55 - 59
• Main Authors: Wishnick, M, Lane, M D
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 01.01.1969
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(19)78190-3

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 ( K i = 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 Mg 2+ and HCO 3 - . 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 14 C 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 14 C-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 Mg 2+ is without effect on 14 C-ribulose-1,5-di-P binding in the presence of cyanide or on 14 C-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.