PRIMARY STRUCTURE OF A 15-KDA PROTEIN FROM RAT INTESTINAL EPITHELIUM - SEQUENCE SIMILARITY TO FATTY-ACID-BINDING PROTEINS

An abundant and novel cytosolic protein was purified from the rat intestinal epithelium by gel filtration, ion-exchange and hydroxylapatite chromatography. The protein was eluted into two different positions (fractions 1 and 2) on DEAE-cellulose chromatography. We have completed the primary structure of the protein of fraction 1 by Edman degradation. The protein (144565 Da) contains 127 amino acid residues and has an acetylated alanine at its NH2-terminus. Comparison of the primary structure of the protein with porcine gastrotropin [Walz, A. D., Wider, M. D., Snow, J. W., Dass, C. & Desiderio, D. M. (1988) J. Biol. Chem. 263, 14189-14195] and rat hepatic fatty-acid-binding protein revealed that identical residues within these proteins are found in 90 and 54 out of a total of 127 positions, respectively. Bioactivity studies demonstrated that neither the protein nor liver and intestinal fatty-acid-binding proteins influence gastric acid secretory activity in rats with gastric fistulas compared to pentagastrin. The protein showed very low affinity for palmitic-acid-binding in vitro assay system and only trace amounts of endogenous fatty acids were detected from the protein. The protein, rat intestinal 15-kDa protein is considered to be a new member of the fatty-acid-binding protein family based on its structural features.