Purification and partial characterization of cellular retinoic acid-binding protein from human placenta

Cellular retinoic acid-binding protein (CRABP) has been purified to homogeneity from human placenta by a series of procedures, including acetone powder extraction, gel filtration on Sephadex G-50, and ion-exchange chromatography on DEAE-cellulose and on SP-Sephadex. Cellular retinol-binding protein (CRBP) was isolated concurrently. CRABP was purified 75,400-fold, based on total soluble acetone powder extract of placenta. The protein is a single polypeptide chain with a molecular mass of 14,600 Da, estimated by sodium dodecyl sulfate (SDS) gel electrophoresis or gel filtration, and has an isoelectric point of 4.78 (apo-CRABP, 4.82). On analysis of absorption and fluorescence spectra, the protein was seen to exhibit an absorption peak at 350 nm, fluorescence excitation maxima at 350 and 370 nm, and a fluorescence emission maximum at 475 nm. Human CRABP was immunologically distinct from human CRBP and serum retinol-binding protein.