Nicotinamide N-oxide reductase activity in bovine and rabbit eyes

The nicotinamide N-oxide reductase activity of a variety of ocular tissues was investigated. The 9,000g supernatant of ciliary body, retinal pigment epithelium-choroid, iris, retina and cornea, but not lens, exhibited reductase activity under anaerobic conditions when supplemented with 2-hydroxypyrimidine, an electron donor of aldehyde oxidase. Among these tissues, the highest activity was observed with ciliary body. When the 9,000g supernatant of ciliary body was fractionated, the 2-hydroxypyrimidine-linked reductase activity was mainly associated with the cytosolic fraction and was markedly inhibited by menadione, an inhibitor of aldehyde oxidase. Similarly, in the presence of 2-hydroxypyrimidine, the cytosolic fraction of rabbit ciliary body exhibited nicotinamide N-oxide reductase activity which was susceptible to inhibition by menadione. These facts strongly suggest that aldehyde oxidase present in mammalian eyes is involved in the reduction of nicotinamide N-oxide to nicotinamide.