Cellular retinoic acid binding protein is associated with mitochondria.

We report that immunohistochemical staining for cellular retinoic acid-binding protein (CRABP) was restricted to the cytoplasm of cortical cells in bovine adrenal. In contrast, staining for the similar protein, cellular retinol-binding protein (CRBP), was found throughout these cells. After transfections of CRABP and CRBP into cultured cells, immunofluorescence analyses again revealed cytoplasmic restriction only for CRABP, with a pronounced punctate appearance. Use of organelle-specific fluorochromes indicated that CRABP immunofluorescence overlaid exactly with the pattern of the mitochondrial-specific fluorochrome. Confirmation of this association came with subcellular fractionation of the adrenal cortex. CRABP, but not CRBP, co-sedimented with the mitochondria, a novel finding for a member of this superfamily of cellular lipid-binding proteins.