Purification and structural characterization of a fatty acid-binding protein from the liver of the catfish Rhamdia sapo

Abstract

We report here the isolation of a fatty acid-binding protein (FABP) from the liver of the catfish Rhamdia sapo. The purification procedure involves gel filtration, anion-exchange chromatography and reverse-phase high-performance liquid chromatography. The purified protein is basic (pI > 8.7) and migrates on sodium dodecyl sulfate-gel electrophoresis as a single entity of about 15 kDa. Its amino acid composition resembles those of FABPs isolated from other animals. Unlike mammalian liver FABPs, catfish liver FABP contains at least one tryptophan residue per molecule. No significant cross-reactivity was observed between the purified protein and polyclonal antibodies against either rat liver FABP or rat heart FABP. Amino acid sequencing of peptides obtained by digestion with Lys-C revealed that the catfish protein is structurally more similar to chicken liver FABP (69% identity in a 67-residue overlap) than to human liver FABPs (36%), nurse shark ( Ginglymostoma cirratum) liver FABP (30%) and human heart FABP (31%). Taken together, these results suggest that catfish liver FABP is far more closely related to chicken liver FABP than to the FABPs isolated from the liver of mammals or elasmobranchs.