Some kinetic properites of liver ornithine carbamoyl transferase (OCT) in a patient with OCT deficiency.

Some kinetic properties of liver OCT from a patient with OCT deficiency were studied. Contrary to controls, in which two pH optima were observed (pH 7.7 and pH 8.5), only the pH optimum of 8.5 could be demonstrated in our patient. From KM studies at pH 7.7 and pH 8.5, the most striking abnormalities in comparison with human controls were (a) a strongly increased KM (ornithine) at pH 7.7, but less pronounced at pH 8.5, (b) a higher VMAX at pH 8.5 compared with the VMAX at pH 7.7 and (c) the absence of substate inhibition at pH 8.5 to ornithine was elevated up to a concentration above approximately 1.5 mM.