Adsorption inhibition as a mechanism of freezing resistance in polar fishes.

Abstract

Polar fishes are known to have serum proteins and glycoproteins that protect them from freezing, by a noncolligative process. Measurements of antifreeze concentrations in ice and scanning electron micrographs of freeze-dried antifreeze solutions indicate that the antifreezes are incorporated in ice during freezing. The antifreezes also have a pronounced effect on the crystal habit of ice grown in their presence. Each of four antifreezes investigated caused ice to grow in long needles whose axes were parallel to the ice c axis. Together these results indicate the antifreezes adsorb to ice surfaces and inhibit their growth. A model in which adsorbed antifreezes raise the curvature of growth steps on the ice surface is proposed to account for the observed depression of the temperature at which freezing occurs and agrees well with experimental observations. The model is similar to one previously proposed for other cases of crystal growth inhibition.In many parts of the polar and subpolar seas, water temperatures fall to as much as 10 below the equilibrium freezing point of fishes' body fluids. Avoidance of freezing in many fishes inhabiting these regions has been linked to the presence of unusual serum proteins and glycoproteins (1-3). These "antifreezes" are not found in temperate-water fishes, and they disappear in summer in those polar fishes that experience warmer summer temperatures (1, 4). Some polar fishes do not have an antifreeze, however, and avoid freezing by existing in a supercooled state in ice-free, deeper waters (5). Fishes possessing an antifreeze are generally found in shallow waters where ice particles are abundant.The glycoprotein antifreeze of the antarctic Trematomus borchgrevtnki consists of a repeating tripeptide, Ala-Ala-Thr, with the disaccharide galactose-N-acetylgalactosamine attached to each threonyl residue, and it is found in eight discrete molecular weights (6). In the smaller fractions (glycoproteins 6-8), an Ala-Ala-Thr unit is occasionally replaced by Pro-Ala-Thr. The antifreeze of the Alaskan saffron cod, Eleginus gracilis, appears to be similar to glycoproteins 6-8 except that threonine is occasionally replaced by arginine (3, 7). Carbohydrate-free protein antifreezes from the Nova Scotia winter flounder, Pseudopleuronectes americanus (8), and the Alaskan sculpin, Myoxocephalus verrucosus (3), like the glycoproteins, consist of roughly 60% alanyl residues. A partial sequence of the flounder antifreeze lacked a repeating tripeptide (9). The antifreezes make a negligible contribution to the osmotic strength of the fishes' body fluids and thus cause a depression of the "freezing point" by some means other than by a colligative process. This view is supported by the fact that the antifreezes lower the temperature at which ice growth occurs but not the temperature at which ice melts (10). It has been suggested (10-12) that, instead of acting in the liquid phase as do most solutes, the antifreezes adsorb to the ice surface and thereby prevent it from growing. We present here ev...

How insects survive the cold: molecular mechanisms—a review

“…Antifreeze proteins (AFPs) depress the freezing point of fluids by adsorbing to seeded ice crystals and inhibiting their growth (Raymond and DeVries 1977). AFPs lower the freezing temperature below the melting point, a phenomena known as thermal hysteresis (TH).…”

Increased flexibility decreases antifreeze protein activity

“…Discovered in fish, 2 arthropods, 3 plants, 4 fungi, 5 and bacteria, 6 AFPs are thought to function by what is known as the Kelvin effect-the protein binds to the ice surface and forces the ice to grow as a curved front, at which point further ice growth becomes inhibited. 7,8 The macroscopic, noncolligative nature of the freezing point depression results in a difference between the freezing and melting points of the solution. This difference is known as TH and is typically used to quantitate the ice-growth inhibition capabilities of an AFP.…”

A Diminished Role for Hydrogen Bonds in Antifreeze Protein Binding to Ice

“…This operational definition was introduced to standardize thermal hysteresis measurements when it became apparent that some AFP mutants exhibit slow ice crystal growth prior to a defined freezing end-point, and others grow so rapidly that a distinguishable end-point is not observed. All measurements were made in 0.1 M NH 4 (23,24), NOESY spectra (25,26) with mixing times from 100 to 300 ms and a TOCSY experiment (27) using a dipsi-2 spinlock field with 68 ms mixing time. The DQF-COSY experiment used a presaturation pulse of 1.5 s for water supression, while the latter two experiments included watergate solvent supression (28).…”