Carbamyl phosphate synthetase I deficiency with no detectable mRNA activity

In the autopsied liver of a neonate with carbamyl phosphate synthetase (CPS)-I deficiency, the activity of CPS-I was about 9% of the normal neonatal control. The enzyme protein of CPS-I was hardly detectable by sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS/PAGE) and an immunoblotting method using anti-rat liver CPS-I. The level of translatable mRNA for CPS-I was markedly decreased in a cell-free protein synthesis system consisting of rabbit reticulocyte lysate and total RNA extracted from the autopsied liver of the patient. These observations indicate that the enzyme deficiency in this case is probably mainly due to a diminished level of translatable mRNA, which would lead to a decrease in the synthesis of the CPS-I precursor.