Demonstration of a novel molecular species in chick embryo brain: Cellular retinol-binding protein, F-type.

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Abstract
By sucrose density gradient sedimentation analysis, a cytosol component of small molecular size which bound 3H-retinoic acid was detected in the chick embryo brain, exhibiting a peak on day 14 (7 days before hatching). In general, cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein (CRABP) were distinguished by showing binding specificity for retinol or retinoic acid, respectively. The component found in embryo brain cytosol exhibited binding affinity for both retinol and retinoic acid, being similar in less ligand-specificity to CRBP (F) which was originally recognized in fish eye cytosol. The component showed a lack of binding affinity for prealbumin (PA), excluding the possibility that chicken plasma retinol binding protein was contaminated in the cytosol. A distinct molecular species of cellular binding protein for vitamin A apparently exists in the brain cytosol of a developing chick embryo.