STRUCTURE AND FUNCTION OF CARBAMOYLPHOSPHATE SYNTHASE .I. TRANSITIONS BETWEEN 2 CATALYTICALLY INACTIVE FORMS AND ACTIVE FORM

Carbamoylphosphate synthase of rat liver has been purified to a homogeneous state. Its molecular weight is about 250,000. When the catalytic activity is measured at 10°, using an optical method, an activation phase is detectable, which could be assigned to the N‐acetyl‐l‐glutamate induced transition of the enzyme from an inactive conformation to the active conformation. The half‐time of the process is about 1 min at 10 mM acetyl‐glutamate. The specific effect of the cofactor was found to be the labilization of the inactive conformation (as opposed to a stabilization of the active conformation). At low temperatures the enzyme dissociates reversibly into probably two identical subunits. The dissociation seems to occur at the stage of the active conformation. ATP was found to hold back the dissociation by specifically stabilizing the active conformation. Copyright © 1968, Wiley Blackwell. All rights reserved