The amino acid sequence of a lamprey ( Entosphenus japonicus) liver fatty acid-binding protein identified its close relationship to cardiac fatty acid-binding proteins of Mammalia

Abstract

Fatty acid-binding proteins (FABPs) constitute a large, tissue-specific multigene family in animals. While liver FABPs of Aves, Reptilia, and Amphibia are close homologs of mammalian liver FABPs, the shark liver protein belongs to the mammalian heart FABP subfamily. We purified an FABP from the liver of lamprey, Entosphenus japonicus, by gel filtration and anion-exchange chromatography. Amino acid sequences determined for lysyl endopeptidase peptides covered nearly the entire molecule except for N- and C-terminal short segments. Examination of the phylogenetic relationship from the sequence identified the lamprey liver protein as a member of mammalian heart-type FABPs. Since livers of bony fish contain both hepatic and cardiac FABPs, expression of the FABP gene in the vertebrate liver appears to change from the heart-type to liver-type within Pisciformes, with bony fish being in a transition stage. This may be related to the evolutionary and physiological divergence of liver function and lipid metabolism of these lower vertebrates.