Purification and properties of cellular retinoic acid-binding protein from neonatal rat skin

Cellular retinoic acid-binding protein (CRABP) was detected in cytosolic extracts of dermis and epidermis of neonatal rat skin using high-performance size-exclusion liquid chromatography and was more abundant in dermal tissue. CRABP was purified 1000-fold from an acid-precipitated, 50,000 x g supernatant of neonatal rat skin by ion-exchange chromatography on DEAE-Sephacel, followed by chromatofocussing and hydrophobic-interaction chromatography. The protein had an apparent Mr of 14,800. In chromatofocussing experiments the apoprotein and holoprotein gave different elution profiles, indicating a charge difference between the two forms. The ability of various retinoids to compete with all-trans-retinoic acid for binding to CRABP was assayed: 4-oxoretinoic acid and two synthetic retinoids were effective competitors, but 13-cis-retinoic acid, 3,4-didehydroretinoic acid and the acid derivative of etretinate competed poorly. The binding protein had a Kd for all-trans-retinoic acid of 8 nM using a dextran-charcoal assay, but a higher value was obtained using high-performance size-exclusion liquid chromatography. The holoprotein dissociated rapidly at room temperature and had a half-life of 4.7 min. At 0 degrees C, the holoprotein had a half-life of 200 min.