Ornithine carbamoyltransferase deficiency. A new variant with subnormal enzyme activity.

A new ornithine carbamoyltransferase variant is described with a nearly normal specific enzymatic activity. This new variant is characterized by a ten-fold increased Km value for L-ornithine (3.75 vs. 0.33 mmol/l in control) and by a normal Km value for carbamoylphosphate (0.42 vs. 0.29 mmol/l). Its pH optimum is shifted towards the alkaline side. This enzyme is highly unstable at 55 degrees C.