BOVINE EPIDERMAL FATTY-ACID-BINDING PROTEIN - DETERMINATION OF LIGANDSPECIFICITY AND CELLULAR-LOCALIZATION IN RETINA AND TESTIS

The fatty acid-binding protein (FABP) family consists of small, cytoso lic proteins believed to be involved in the uptake, transport, and sol ubilization of their hydrophobic ligands. Members of this family have highly conserved sequences and tertiary structures. Using an antibody against testis lipid-binding protein, a member of the FABP family, a p rotein was identified from bovine retina and testis that coeluted with exogenously added docosahexaenoic acid during purification. Amino aci d sequencing and subsequent isolation of its cDNA revealed it to be ne arly identical to a bovine protein expressed in the differentiating le ns and to be the Likely bovine homologue of the human epidermal fatty acid-binding protein (E-FABP). From quantitative Western blot analysis , it was estimated that bovine E-FABP comprised 0.9%, 0.1%, and 2.4% o f retina, testis, and lens cytosolic proteins, respectively. Binding s tudies using the fluorescent probe ADIFAB indicated that this protein bound fatty acids of differing levels of saturation with relatively hi gh affinities. K-d values ranged from 27 to 97 nM. In addition, the pr otein was immunolocalized to the Muller cells in the retina as well as to Sertoli cells in the testis. The location of bovine E-FABP in cell s known to be supportive to other cell types in their tissues and the ability of E-FABP to bind a variety of fatty acids with similar affini ties indicate that it may be involved in the uptake and transport of f atty acids essential for the nourishment of the surrounding cell types .