LOCALIZATION OF CELLULAR RETINOL-BINDING PROTEIN IN BOVINE RETINA AND RETINAL-PIGMENT EPITHELIUM, WITH A CONSIDERATION OF PIGMENT EPITHELIUM ISOLATION TECHNIQUE
Bovine RPE [retinal pigment epithelium] was isolated by commonly used brushout procedures and analyzed by light microscopy and EM. The preparation consisted almost entirely of cells with retained organelles (mitochondria, pigment and other granules) but with broken surface membranes and extracted cytoplasm. The wash obtained by sedimenting these broken cells contained approximately 97% of the cellular retinol-binding protein present in the suspension. Cellular retinoic acid-binding protein, present in bovine retinal extracts, was found in low amounts in the wash from RPE. The cellular retinol-binding protein present in the RPE wash was of high specific activity and similar in properties to that obtained from bovine retina. Supernatant obtained from sonicated rod outer segments contained approximately 10% of the retinol-binding protein of the retina. No retinoic acid-bindig protein was found. The relatively large amount of cellular retinol-binding protein present in the RPE (more than in the retina) was consistent with a functional role of this protein in uptake and transport of retinol by the RPE.