TIME-COURSE OF THE URIDYLYLATION AND ADENYLYLATION STATES IN THE GLUTAMINE-SYNTHETASE BICYCLIC CASCADE

A kinetic analysis of the glutamine synthetase bicyclic cascade is pre sented. It includes the dependence on time from the onset of the react ion of both the uridylylation of Shapiro's regulatory protein and the adenylylation of the glutamine synthetase. The transient phase equatio ns obtained allow an estimation of the time elapsed until the states o f uridylylation and adenylylation reach their steady-states, and there fore an evaluation of the effective sensitivity of the system. The con tribution of the uridylylation cycle to the adenylylation cycle has be en studied, and an equation relating the state of adenylylation at any time to the state of uridylylation at the same instant has been deriv ed.