Abstract
cDNA clones encoding myosin light chains (A 1-, A 2-, and DTNB-LC) were isolated from fast skeletal muscles of eight marine teleosts and amino acid sequences were deduced from cDNA nucleotide sequences. The A1-LC from all fish examined was highly conserved in their primary structures as in the case of DTNB-LC and contained a so-called difference peptide of amino acid residues rich in alanine and praline in the N-terminal region, which was absent in A 2-LC. However, the N-terminal sequence of fish A 2-LC was markedly species-specific. Bottom fish such as walleye pollack and white croaker had conventional A 2-LC that lacked the difference peptide. On the other hand, A 2-LC from horse mackerel and mackerel-scad showed N-terminal amino acid sequences similar to that of difference peptide, although their peptide length of about 10 residues was much shorter than the conventional difference peptide. Furthermore, sardine and Scombroid fish such as tuna and skipjack contained A 2-LC with difference peptide-like sequences of about 21 residues in their N-terminal region. These results imply that N-terminal peptides of A 2-LC specific to pelagic fish have physiological functions to facilitate effective swimming in these fish. Such evidence for high A 2-LC species-specificity at the molecular level confirmed practical application of LC patterns in various electrophoretic analyses for fish species identification and classification.
