Effect of potassium cyanate on the catalytic activities of carbamyl phosphate synthetase1

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Summary

Potassium cyanate has the following effects on the catalytic activities exhibited by carbamyl phosphate synthetase (from E. coli): Glutamine-dependent carbamyl phosphate synthesis and ATP- and bicarbonate-dependent L-γ-glutamyl hydroxamate hydrolysis activities are inhibited, bicarbonate-dependent ATPase activity is stimulated by nearly 3-fold, synthesis of ATP from carbamyl phosphate and ADP is not affected, and the apparent Km value for ammonia in the ammonia-dependent carbamyl phosphate synthesis reaction is decreased. Saturation kinetics are obtained when the effect of cyanate concentration is measured, and half maximal effect of cyanate is observed with a concentration of about 2 mM. These effects of potassium cyanate thus closely resemble those observed after treatment of this enzyme with L-2-amino-4-oxo-5-chloropentanoic acid. The present studies strongly suggest that cyanate, like the chloroketone, reacts at the glutamine binding site on the light subunit of the enzyme.

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1

Supported in part by Publich Health Service Grant AM11443

2

Current address: Thomas Hunt Morgan School of Biological Sciences, University of Kentucky, Lexington, Kentucky 40506

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