Decarbamoylating activity of ornithine transcarbamoylase

We have purified from beef liver an enzyme which decarbamoylates carbamoyl-hemoglobin and to a much lesser extent carbamoyl histones. Carbamoyl casein was a poor substrate while carbamoyl trypsin, fibrinogen and ovoalbumin were not affected. The optimal pH is 7.4. Addition of Mg++, Mn++ or Ca++ was without effect. On testing citrulline as a substrate we found high activity leading us to suspect that the activity of the decarbamoylase preparation was due to contaminating ornithine transcarbamoylase activity. Evidence for this is the similar ratio of transcarbamoylase to decarbamoylase activities of both ornithine transcarbamoylase and of the purified preparation of decarbamoylase from beef liver. Also, delta-PALO, the specific inhibitor of ornithine transcarbamoylase inhibited both preparations to the same extent. Interestingly, ornithine transcarbamoylase from bacteria also has decarbamoylase activity while aspartic transcarbamoylase does not.