PURIFICATION AND CHARACTERIZATION OF ANTIFREEZE PROTEINS FROM LARVAE OF THE BEETLE DENDROIDES-CANADENSIS

Four antifreeze proteins (AFPs) were purified from larvae of the beetle Dendroides canadensis. The AFPs are similar in amino acid compositions, having high contents of hydrophilic amino acids (45-55 mol%) and cysteine (approximately 16 mol% Cys). Approximately half of the Cys residues form disulfide bridges, and both the disulfide bridges and free sulfhydryls are essential for activity. The N-terminals of the AFPs are blocked. The pH optimum of the AFPs is approximately 7.8, but major loss of activity occurred only at very high pH (12.0). The detergents SDS and Triton X-100 did not inactivate the AFPs. Circular dichroism spectra indicate the presence of both alpha and beta-secondary structures in the AFPs, in addition to a large random structure component.