Separation and differential sensitivity toward avidin of carbamyl phosphate synthetase and urea amidolyase.

This enzyme is remarkably sensitive to inhibition by highly purified egg white avidin, a phenomenon which can be completely prevented by inclusion of excess biotin in the assay system. Inasmuch as avidin has been found to selectively inhibit all known biotinenzymes and, indeed, is now accepted as a diagnostic tool for the detection of such reactions [2], the proposal was made that UALase belongs to that class of enzymes which contain biotin in the form of a bound, functionally-active prosthetic group. A recent publication by Wellner, Santos and Meister [3], asserting that the glutamine-dependent carbamyl phosphate synthetase (CPSase, EC 2.7.2.5) of Escherichia coli may also be a biotinznzyme, has focused our attention on the relevant question of whether these two enzymic processes might possibly represent analogous activities of the same protein molecule. At this time we wish to report results which indicate that not only is each reaction catalyzed by a