Ornithine delta-aminotransferase activity in retina and other tissues

Ornithine delta-aminotransferase (OAT) activity was determined in liver, kidney, brain, retina and ciliary body-iris of rat, rabbit, calf and human. OAT activities (nanomoles delta 1-pyrroline-5-carboxylate/mg protein/hr) in retina were (mean +/- SE) 324 +/- 43, 240 +/- 24, 234 +/- 26 and 218 +/- 22 respectively in rat, rabbit, calf and human. The OAT activities in retina were three times higher than in brain and 80% of that of liver. 2-oxoglutarate was the preferred amino acceptor substrate for OAT activity. In rat retina the activities of OAT with glyoxalate, beta-hydroxypyruvate, pyruvate, and oxaloacetate were 51, 44, 30, and 30% of that of 2-oxoglutarate respectively. A lack of substrate OAT specificity indicates OAT deficiency such as occur in gyrate atrophy of the choroid and retina could impair metabolism of ketoacids. A candidate for possible toxicity to the retina in OAT deficiency is glyoxalate. Arginine glycine transamidinase activity was not detectable in human retina, thus a previously postulated creatine phosphate deprivation in OAT deficiency may not be applicable to the pathogenesis of the disease.