Molecular aspects of urea cycle enzymes and related disorders

Amino acid sequence of rat ornithine transcarbamylase (OTC) precursor containing an NH2-terminal presequence of 32 residues was deduced from the cDNA sequence. Comparison with the human and Escherichia coli enzymes indicated that regions containing the putative binding sites for the substrates are highly conserved among the three species. cDNA clones for rat and human liver arginase were isolated and predicted amino acid sequences were compared with that of the yeast enzyme. There are several regions highly conserved among the three species which may be important for catalysis. Several cases of carbamyl phosphate synthetase I and OTC deficiencies were analyzed for enzyme activity, enzyme amount and mRNA activity.