Abstract
L-Ornithine:2-oxoacid aminotransferase (OAT) is a mitochondrial matrix enzyme, present in most tissues (1). It catalyses the transfer of the terminal (S) amino group of L-ornithine (2,5-diamino-pentanoic acid) (Orn) to 2-oxoglutarate, producing glutamic acid semi-aldehyde and glutamic acid (2). It has been suggested many years ago that OAT competes with L-ornithine carbamoyltransferase (OCT) for the intramitochondrially available Orn, and thus decreases the rate of urea formation via the urea cycle (3). In favor of this suggestion are protective effects of large doses of Orn and arginine (Arg) in acute ammonia intoxication (4,5). Administration of these amino acids is assumed to enhance mitochondrial Orn concentrations and thus increase due to the improved substrate availability the rate of both reactions, citrullin (Cit) formation and transamination. Inhibition of OAT and the consequent increase of Orn concentrations in liver appeared to be a potential alternative to the administration of Orn.
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