The carbamyl phosphate content of rabbit blood plasma

Rabbit blood plasma was analyzed for the presence of carbamyl phosphate by incubating freshly collected plasma with aspartate-C 14 and aspartate transcarbamylase. No measurable concentration of carbamyl phosphate was found. Control experiments showed good recovery of added carbamyl phosphate so that it can be concluded that rabbit plasma contains less than 5 × 10 −6 M carbamyl phosphate. The implications of this finding with regard to the de novo synthesis of pyrimidines in mammals is discussed.