And AFGPs

Water and AFGP solution was initially frozen at -3°C and then allowed to melt at +0.1°C until 5-10% of solution remained as ice crystals. The temperature was then adjusted to 0.0°C and periodically lowered and then raised as indicated. The times at each temperature intermediate between freezing and melting were 5-10 minutes. All observations were made microscopically. 

B. Effects of Freezing Solutions of AFGP on the Characteristics of the Ice and AFGP... 

AFGP-7 and AFGP-8 have very weak activity when tested alone but show extensive antifreeze activity in mixtures with AFGP-1 to AFGP-5 under certain conditions. 

Mixtures of AFP and AFGP-1 to AFGP-5 recently have shown additive increments in lowering the freezing temperature (37). Thus, they appeared to act independently of one another. However, as might be expected, mixtures of AFP and AFGP-8 did not exhibit potentiation. 

A unique family of O-linked glycoproteins permits fish to live in the icy seawater of the Arctic and Antarctic regions where water temperature may reach as low as — 1.9°C. Antifreeze glycoproteins (AFGPs) are found in the blood of nearly all Antarctic fish and at least five Arctic fish. These glycoproteins have the peptide structure... 

Figure 7.39. The diversity of antifreeze proteins and antifreeze glycoproteins in marine fishes. Shown are the structures of four types of AFPs (I-IV) and the AFGP found in Antarctic notothenioids and Arctic cod. AFPs I-IV are shown as ribbon structures. The tripeptide repeat (-ala-ala-thr-) and carbohydrate moiety (galactosyl-lV-acetylgalactosamine) of AFGPs illustrate the key element of AFGP structures in noto-thenioid and Arctic cod.

The ability to inhibit the growth of ice has potential medical, industrial and commercial applications. Unfortunately, many of these applications have not been fully realized. One reason for this is that the isolation and purification of AFGP is a laborious and costly process often resulting in mixtures, making characterization difficult (5). Additional reasons include the fact that the AFGP mechanism of action is not understood at the molecular level and the nature of the protein-ice interface remains in question (6). 

AFGP analogs 9, 10 and 11 were also tested for TH activity using nanoliter osmometry at concentrations identical to those used in the RI assay. These measurements confirm that 10 and 11 induce a small thermal hysteretic gap of 0.056 °C (30 mosmol). Initially we were bothered by the fact that 10 and 11 appeared to display similar activity in the TH assays and different activity in the RI assay. However, recent results have shown that the relationship between RI and TH activity is qualitative and not quantitative (34). 

Table II. Effect of Hydroxide Ion Concentration and Calcium Ion on Initial Rate of 3 Elimination of Phosvitin and Antifreeze Glycoprotein-8 (AFGP-8)...

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