THE UNDERLYING biochemical disorder in this condition is an absence of liver arginosuccinic acid lyase.2 This has now been shown by an estimation of the activities of the enzymes of the urea cycle in a liver biopsy. Ornithine transcarbamylase, arginase, and carbamyl phosphate synthetase activities were found normal, but no arginosuccinic acid lyase activity was detected. Surprisingly, the arginosuccinic acid synthetase was nearly three times as active as acid found in two other liver biopsies, and twice as high as normal values reported by others. Arginosuccinase was also absent in the patient's red blood cells (Tables 1 and 2).
The same considerations apply here as to the treatment of hyperammonemia. When it was originally thought that the symptoms derived only from the presumed toxic nature of arginosuccinic acid, treatment was directed towards reducing the amount of this amino acid formed. The effects of various alterations in the protein