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

Abstract

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 K m 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.