The role of endogenous antifreeze protein enhancers in the hemolymph thermal hysteresis activity of the beetle Dendroides canadensis

Antifreeze proteins (AFPs) lower the freezing point of water by a non-colligative mechanism, but do not lower the melting point, therefore producing a difference between the freezing and melting points termed thermal hysteresis. Thermal hysteresis activity (THA) of AFPs from overwintering larvae of the beetle Dendroides canadensis is dependent upon AFP concentration and the presence of enhancers of THA which may be either other proteins or low molecular mass enhancers. The purpose of this study was to determine the relative contributions of endogenous enhancers in winter D. canadensis hemolymph. hemolymph collected over four successive winters (1997–1998 to 2000–2001) was tested. The first three of these winters were the warmest on record in this area, while December of the final year was the coldest on record. Protein and low molecular mass enhancers raised hemolymph THA 60–97% and 35–55%, respectively, based on hemolymph with peak THA for each year collected over the four successive winters. However, the hemolymph AFPs were not maximally enhanced since addition of the potent enhancer citrate (at non-physiologically high levels) resulted in large increases in THA. 13NMR showed that glycerol was the only low molecular mass solute present in sufficiently high concentrations in the hemolymph to function as an enhancer. Maximum THA appears to be ∼8.5 °C.