Ming H. Kao

Lethal freezing temperatures of Arctic char and other salmonids in the presence of ice

Abstract The lethal freezing temperatures of seawater acclimated Arctic char (Salvelinus alpinus), brook trout (Salvelinus fontinalis), Atlantic salmon (Salmo salar), brown trout (Salmo trutta) and rainbow trout (Salmo gairdneri) were determined in the presence of ice. Arctic char showed the greatest resistance to freezing (−0.99°C) followed by brook (−0.87°C) and brown trout (−0.81°C) and by salmon (−0.76°C) and rainbow trout (−0.75°C). Plasma electrolyte levels accounted for 90–95% of the observed freezing temperature values. However, the lethal freezing temperatures of all of the salmonids were significantly lower than their plasma freezing temperatures, suggesting that at least one other factor was involved in preventing the fish from freezing. This difference between fish freezing temperature and plasma freezing temperature was greatest in Arctic char (0.2°C) and accounted for 70% of the difference in freezing resistance between char and salmon. It is hypothesized that the chars epidermis acts as a barrier to prevent ice propagation.

Antifreeze glycoproteins: relationship between molecular weight, thermal hysteresis and the inhibition of leakage from liposomes during thermotropic phase transition.

Antifreeze glycoproteins (AFGP) were isolated and purified from the blood plasma of rock cod (Gadus ogac), using DEAE-Bio-gel ion exchange chromatography, followed by high performance liquid chromatography (HPLC). The purified proteins were analyzed using polyacrylamide gel electrophoresis (PAGE), and electrospray mass spectrometry. The results indicated that rock cod synthesize seven size classes of glycoproteins, ranging from 2.6 to 24 kDa, with each size class containing multiple isoforms. Antifreeze activity, as determined by thermal hysteresis, indicated that the AFGP could be separated into two groups, with the larger size classes (molecular mass>13 kDa) having approximately 3-4 times the activity of the smaller, proline containing, size classes (molecular mass<10 kDa). All of the AFGP size classes prevented leakage from dielaidoylphosphatidylcholine (DEPC) liposomes as they were cooled through their phase transition temperature, with the larger size classes being approximately 4 times as effective as the smaller ones. It is hypothesized that AFGP prevent liposomes from leaking as they pass through the phase transition temperature by binding to the phospholipid membrane.

Antifreeze proteins in the grubby sculpin, Myoxocephalus aenaeus and the tomcod, Microgadus tomcod: comparisons of seasonal cycles

SynopsisAntifreeze protein levels in the plasma of the grubby sculpin, Myoxocephalus aenaeus and the tomcod, Microgadus tomcod of Long Island coastal waters start to increase by November in anticipation of midwinter freezing conditions. Peak levels of antifreeze, as measured by the difference in plasma melting and freezing points, were detected in January for both species. The thermal hysteresis values reached 0.459°C in sculpin and 0.51°C in tomcod. Antifreeze peptides and glycopeptides start to disappear when water temperatures begin to rise and are at insignificant levels by late spring. Aspects of the seasonal cycle and the level of antifreeze activity were compared in three sympatric species (sculpin, tomcod, flounder); in two closely related but ecologically distinct gadids (tomcod, Atlantic cod); and within the genus Myoxocephalus.

Antifreeze proteins in the urine of marine fish.

Several species of marine teleosts have evolved blood plasma antifreeze polypeptides which enable them to survive in ice-laden seawater. Four distinct antifreeze protein classes differing in carbohydrate content, amino acid composition, protein sequence and secondary structure are currently known. Although all of these antifreezes are relatively small (2.6–33 kd) it was generally thought that they were excluded from the urine by a variety of glomerular mechanisms. In the present study antifreeze polypeptides were found in the bladder urine of winter flounder (Pseudopleuronectes americanus), sea raven (Hemitripterus americanus), ocean pout (Macrozoarces americanus) and Atlantic cod (Gadus morhua). Since the plasma of each of these fish contains a different antifreeze class it would appear that all four classes of antifreeze can enter the urine. The major antifreeze components in the urine of winter flounder were found to be identical to the major plasma components in terms of high performance liquid chromatography retention times and amino acid composition. It is concluded that plasma antifreeze peptides need not be chemically modified before they can enter the urine.

Antifreeze glycoprotein in a “southern” population of atlantic tomcod, Microgadus tomcod

Abstract 1. 1. A Long Island, New York population of the Atlantic tomcod, Microgadus tomcod, initiated antifreeze glycopeptide production in late fall (water temperatures were about 10°C). 2. 2. Significant quantities occurred in midwinter specimens exposed to ice covered marine field conditions and sub-zero temperatures. 3. 3. Increased antifreeze activity over a 3 month period was indicated by an increase in the total freezing point depression from 0.53 to 0.83°C. 4. 4. A reliable estimate of antifreeze activity is the difference between the freezing and melting temperatures of tomcod plasma samples; termed, thermal hysteresis. 5. 5. This thermal hysteresis increased from 0.05°C to approx. 0.5°C in midwinter samples; a value markedly greater than that measured in a comparable New Brunswick tomcod population.