Isolation and characterization of antifreeze glycoproteins from the frostfish, Microgadus tomcod

Abstract

The antifreeze proteins were isolated from frostfish (Microgadus tomcod) using gel filtration and ion exchange chromatography and characterized by high-performance liquid chromatography. The antifreeze proteins were glycoproteins which appeared to consist of at least six components with molecular weights ranging from 2 550 to 32 200. Chemical analysis of the larger components showed a predominance of alanine, threonine, and galactosamine. The smaller peptides contained proline and arginine in addition to alanine and threonine. The amino acid sequence of the smallest glycopeptides (molecular weight 2 550) was found to be Ala-Ala-Thr-Ala-Ala-Thr-[Formula: see text]-Ala-Thr-Ala-Ala-Thr-Pro-Ala-[Formula: see text]-Ala-Ala.These glycopeptides are very similar in amino acid and carbohydrate composition to those isolated from the Antarctic nototheniids and several northern gadoids. The sequence of the first 14 amino acids of smaller glycopeptides from the frostfish is identical to comparable peptides found in the nototheniids and the saffron cod. To date arginine has only been observed in the glycopeptide antifreezes of the frostfish and the saffron cod.