Purification, characterization, and partial amino acid sequencing of an amphibian liver fatty acid binding protein

The fatty acid binding protein (FABP) from toad liver cytosol was purified to homogeneity by a procedure involving gel filtration and anion exchange chromatography. The protein presented a molecular mass of 13 987 +/- 2 daltons determined by electrospray mass spectrometry. Native isoelectric focusing of the purified liver FABP revealed a single pI 6.8 band. On the other hand, the toad heart FABP showed a different mobility than that of load liver FABP by both sodium dodecyl sulfate polyacrylamide gel electrophoresis and isoelectric focusing. Moreover, toad liver FABP cross-reacted with antisera to mammalian liver FABP but not with antisera to heart FABP. The difference between toad liver and heart FABPs was further confirmed by partial ami no acid sequencing. As the N-terminus of toad liver FABP was blocked, the protein was chemically and enzymatically cleaved and the resulting peptides were subjected to automated Edman degradation. Partial amino acid sequencing showed that the toad liver FABP is related to that of mammalian liver and is clearly different from the amphibian heart FABP as well as from the amphibian intestine FABP.