Antifreeze agents of terrestrial arthropods

Abstract

1. 1. Many insects and other terrestrial arthropods which overwinter in exposed sites in temperate and polar regions are freeze-susceptible (unable to survive freezing) and therefore the seasonal production of antifreezes is critical for their survival. 2. 2. Many of these freeze-susceptible terrestrial arthropods employ low molecular weight antifreezes. such as polyols and sugars. These solutes lower the supercooling point of the insect approximately 2 × more than they lower the melting point. 3. 3. Proteins, similar to the antifreeze proteins and glycoproteins of polar marine fishes, which produce a thermal hysteresis (differences between freezing and melting points) of several degrees function as antifreezes in a number of insects, spiders and a centipede. In some species these proteins are the only identifiable antifreezes, while in other species polyols are also produced. 4. 4. Temperature and photoperiod are the most important environmental cues used to trigger the production and loss of the thermal hysteresis proteins (THP's). The physiological timing processes which control antifreeze levels involve the insect's circadian system. 5. 5. Several insect THP's have now been purified and their compositions analyzed. In general, these insect THP's have more hydrophilic amino acids and a much lower alanine content than fish THP's. Perhaps the most interesting of the insect THP's is one from Tenebrio molitor, which contains 28% cysteine residues.