Thermal hysteresis

Abstract

Antifreeze (glyco)proteins, AF(G)Ps, are defined by their shared ability to prevent ice crystals from growing in supercooled solutions. They are categorized as being either moderately active or hyperactive. The distinct difference in antifreeze potency between these two categories is accompanied by distinct shapes of the ice crystals that are being stabilized in their presence; moderately active AF(G)Ps cause bipyramidal crystals to develop, a shape that only exposes a single crystal plane to the surrounding solution. In the presence of hyperactive AF(G)Ps, ice crystals express several crystal planes. A number of different factors affect their potency as antifreeze agents, from large organic macromolecules to inorganic ions. This chapter outlines current understanding of the modus operandi of AF(G)Ps. Attempts are made to provide some simple explanations to the antifreeze potency of AF(G)Ps, including their characteristics as moderately active or hyperactive, and how their antifreeze potency is affected by different factors. The different potencies of moderately and hyperactive AF(G)Ps are ascribed to differences in their adsorption habits. Effects of additives or molecular size on their potencies are ascribed to variations in protein solubility, induced by variations in molecular size or evoked by the presence of additives. Experimental proof of concept is discussed in the context of basic solubility theory. Some characteristics of ice-nucleating agents (INAs) in relation to AF(G)Ps and their relevance in cold tolerance is also briefly examined.