Purification and partial characterization of a novel cellular retinol-binding protein, type three, from the piscine...

A novel cellular retinol-binding protein, termed type three (CRBP III), was isolated from eyes of the bigeye of tuna. CRBP III showed a molecular weight of 15,400, an isoelectric point of 4.80, alpha 1-mobility in electrophoresis, and a lambda max of 350 nm. All-trans-retinol, the endogenous ligand, could be competitively displaced by retinoic acid but not by retinal. CRBP III was differentiated from purified piscine and rat cellular retinol-binding proteins (CRBP) and cellular retinoic acid-binding proteins (CRABP) by its amino-acid composition, electrophoretic mobility, fluorescence spectra and ligand-binding specificity.