Glycosidases of the retinal pigment epithelium

The pH optima and apparent Km and Vmax values were determined for nine glycosidases of the retinal pigment epithelium (RPE) of the calf. In terms of micromoles of substrate cleaved per milligram protein per hour, the following relative order of enzymatic activities was observed: beta-N-acetylglucosaminidase greater than alpha-glucosidase = beta-N-acetylgalactosaminidase greater than alpha-mannosidase greater than beta-galactosidase greater than beta-glucosidase greater than alpha-fucosidase greater than alpha-galactosidase greater than beta-glucuronidase. The pH optimum of each of these enzymes was in the acidic range (below pH 6). All these findings refer to enzymatic activities of bovine RPE preparations obtained by the brushing procedure of Glocklin and Potts and washing as described by Berman and Feeney. Thus they may relate to those activities associated with particulate components of the RPE cell and not to the more soluble glycosidases. The distribution of the glycosidases between the washes of the cells and the final pellet of bovine RPE cells was examined. The activities of 10 glycosidases in the RPE of the embryonic chick were also examined. Neither beta-mannosidase nor beta-fucosidase activities could be detected in washed bovine RPE cells, although beta-mannosidase was detected in RPE of the embryonic chick. The presence of isoenzymes of beta-glucuronidase in bovine RPE was indicated. Specificity by beta-glucuronidase of bovine RPE for synthetic substrates was observed.