Aspartate transcarbamylase activity in homogenates containing the hydrolase can be measured qualitatively by inhibition of the hydrolase or by raising the carbamyl phosphate concentration to allow for its hydrolysis during the assay. INTRODUCFION

Particles of certain rat tissue preparations contain a phosphate ester hydrolase that destroys carbamyl phosphate. This activity is similar to that of the alkaline phosphatases. Both have the same molar activities, pH curves, and particulate localization. Both are activated when solubilized with 1butanol and are inhibited by adenine nucleotides and inorganic phosphate. Their reactions are not additive in the same assay. They have the same distributions in rat tissues and tumors, with highest activities in adult kidney and in fetal and adult small intestine. The two activities also increase in parallel during development from fetal to adult kidney. Aspartate transcarbamylase activity in homogenates containing the hydrolase can be measured qualitatively by inhibition of the hydrolase or by raising the carbamyl phosphate concentration to allow for its hydrolysis during the assay.