Protein content and freezing avoidance properties of the subdermal extracellular matrix and serum of the Antarctic snailfish, Paraliparis devriesi

The Antarctic snailfish, Paraliparis devriesi (Liparididae), occupies an epibenthic habitat at a depth of 500-650 m in the subzero waters of McMurdo Sound, Antarctica. This species has watery (97%) gelatinous subdermal extracellular matrix (SECM) comprising a mean of 33.8% of the body weight, the largest known proportion of any adult fish. The protein concentration of the SECM was found to be 6-7 mg ml^-1 (0.6-0.7% w/v). Separation of the polypeptides of the SECM by SDS-PAGE revealed 11 polypeptides ranging in relative molecular mass (M_r) from 67,000 to 13,000, with other unresolved polypeptides of less than 13,000. The isoelectric points of these proteins ranged from 4.85 to 8.05. Partial N-terminal amino acid sequence data were obtained for four of the major SECM polypeptides. The N-terminal amino acid sequences of three of these were not identical to or homologous with any other known sequences, whereas the N-terminal sequence of one polypeptide (M_r 51,000) was identical to partial sequence from the apolipoprotein A-I precursor of Atlantic salmon (Salmo salar). Although not isolated from either SECM or serum, melting point-freezing point behavior of body fluids suggest that Paraliparis possess modest amounts of a noncolligative antifreeze compound. Since relatively small amounts of antifreeze are present in the serum and even less in the SECM, freezing avoidance results from the combined effects of antifreeze and the elevated osmolality of body fluids. There are no special adaptations to prevent freezing in the superficially located high water content SECM.