PURIFICATION AND STRUCTURAL CHARACTERIZATION OF A FATTY-ACID-BINDING PROTEIN FROM THE LIVER OF THE CATFISH RHAMDIA-SAPO

We report here the isolation of a fatty acid-binding protein (FABP) fr om the liver of the catfish Rhamdia sapo. The purification procedure i nvolves gel filtration, anion-exchange chromatography and reverse-phas e high-performance liquid chromatography. The purified protein is basi c (pi > 8.7) and migrates on sodium dodecyl sulfate-gel electrophoresi s as a single entity of about 15 kDa. Its amino acid composition resem bles those of FABPs isolated from other animals. Unlike mammalian live r FABPs, catfish liver FABP contains at least one tryptophan residue p er molecule. No significant cross-reactivity was observed between the purified protein and polyclonal antibodies against either rat liver FA BP or rat heart FABP. Amino acid sequencing of peptides obtained by di gestion with Lys-C revealed chat the catfish protein is structurally m ore similar to chicken liver FABP (69% identity in a 67-residue overla p) than to human liver FABPs (36%), nurse shark (Ginglymostoma cirratu m) 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 mamma ls or elasmobranchs.