Cytochrome Biochemistry in Sheep Retina Following Exposure to Oxygen

Abstract

The mitochondrial enzyme cytochrome c oxidase (COX) is abundant in the photoreceptor inner segments and the synaptic layers of the retina where it functions as essential enzyme in oxidative metabolism. Indeed, the neural retina has the highest known rates respiration and glucose oxidation (1,2). However, the greatest concentration of COX is found in the retinal pigment epithelium (RPE) where it presumably functions primarily as an antioxidant. Photoreceptor cells are highly sensitive to oxygen toxicity when oxygen tensions (PO2) are elevated by as little as two fold (3).The photoreceptor cell membrane is particularly susceptible to free radical attack because of its high ratio of docosahexaenoic acid (4). However O2 toxicity might be exacerbated by a direct effect of O2 upon the activity of COX which would diminish its efficiency in both its metabolic role and as an antioxidant.