Ornithine aminotransferase distribution in ocular tissues and retinas of cat and mouse

Ornithine aminotransferase (OAT), a mitochondrial matrix enzyme, is genetically deficient in patients with gyrate atrophy of the choroid and retina. Histologically defined micro-samples (10 ng-6.8 micrograms dry weight) were dissected out from freeze-dried tissue sections of eyeballs of cat and mouse, and the OAT activities were determined by a newly developed microassay method in the ocular tissues and retinal layers. Very high specific activities of OAT, expressed on a dry weight basis, were found in the feline ocular tissues of ectodermal origin, that is, neuroretina, retinal pigment epithelium, ciliary processes and epithelium of iris. In cat and mouse retinas, high OAT activities were distributed in the inner retina with an activity peak in the inner plexiform and ganglion cell layers. Very low activity was present in the outer nuclear layer. The inner segments of photoreceptor cells, which are very rich in mitochondria, contained the highest OAT activity. In contrast, the outer segments of photoreceptor cells contained the low activity resulting from contamination by small pieces of inner segments.