Enzymatic determination of carbamyl phosphate in blood

A specific assay for determination of carbamyl phosphate (carbamyl P) in blood has been developed using the enzymatic conversion of carbamyl P to citrulline by ornithine carbamyl transferase (OCT). This assay, for evaluation of bioavailability of carbamyl P, is necessary for study of the in vivo and in vitro effects of carbamyl P as an antisickling agent. The recovery of carbamyl P as citrulline was 88 to 92 per cent. Carbamyl P in whole dog blood in vitro decomposed with first-order kinetics with a t-1/2 of 42 minutes, the same as the t-1/2 reported for decomposition of carbamyl P to cyanate in buffers at physiologic temperature and pH. When carbamyl P (190 mg. per kilogram) was injected intraperitoneally into mice, it appeared in the blood, with a maximum concentration of 0.2 mM observed between 1 and 5 minutes after injection, followed by a rapid decrease within 10 minutes. The clearance of carbamyl P from dog blood after intravenous injection was first-order, with a t-1/2 of approximately 2.2 minutes. The rapid disappearance of carbamyl P in vivo may possibly by explained by the action of tissue acyl phosphatases which have been reported to hydrolyze carbamyl P.