Urea Ornithine carbamyl transferase

Hyperammonemia occurs in biotin deficiency and the functional deficiency associated with lack of holocarboxylase synthetase (Section 11.2.2.1) and bio-tinidase (Section 11.2.3.1). In deficient rats, the activity of ornithine carbamyl-transferase is two - thirds of that in control animals, as a result of decreased gene expression, although the activities of other urea cycle enzymes are unaffected (Maeda etal., 1996). 

The biomolecular modes of action of ornithine have been the subject of several experimental investigations. Ornithine activates the enzymes carbamylphosphate synthetase and ornithine carbamyl transferase, which are necessary for the liver-specific process of urea synthesis (133,139) this occurs mainly in the periportal hepa-tocytes (= definitive ammonia detoxification). Glutamine synthesis (binding of ammonia to glutamate) takes place predominantly in the perivenous hepatocytes (= transitory ammonia detoxification). Large amounts of glutamate are necessary for this. Aspartate, ornithine... 

Ml Macleod, P., Mackenzie, S. and Scriver, C. R. Partial ornithine carbamyl transferase deficiency, an inborn error of the urea cycle presenting as orotic aciduria in a male infant. Can. Med. Assoc. J., 107, 405-408 (1972)... 

A urea cycle enzyme found mainly in the liver and kidney. High serum levels are found in conditions where there is hepatocellular damage such as hepatitis. A congenital deflciency of the enzyme has also been described (ornithine carbamyl transferase deficiency). 

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