Sphingomyelinase activity in the bovine and human eyes.

We examined biochemically sphingomyelinase activity in the bovine and human ocular tissues, using trinitrophenylaminododecanoylsphingosylphosphorylcholine as substrate. The enzyme activity in the crude extracts of neuroretina, retinal pigment epithelial cells, and optic nerve of the bovine eyes was proportional to protein concentration. The activities in these tissues were little activated with Mg2+ at pH 5.1 but was activated with Mg2+ at pH 7.5. The enzyme activity at pH 5.1 was also detected in the iris and ciliary body, neuroretina, retinal pigment epithelium and choroid, and optic nerve of the human eyes. It was highest in the macula, compared with other areas of the human ocular fundus.