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RiAFP refers to an antifreeze protein (AFP) produced by the ''Rhagium inquisitor'' longhorned beetle. It is a type V antifreeze protein with a molecular weight of 12.8 kDa; this type of AFP is noted for its hyperactivity. ''R. inquisitor'' is a freeze-avoidant species, meaning that, due to its AFP, ''R. inquisitor'' prevents its body fluids from freezing altogether.〔 This contrasts with freeze-tolerant species, whose AFPs simply depress levels of ice crystal formation in low temperatures. Whereas most insect antifreeze proteins contain cysteines at least every sixth residue, as well as varying numbers of 12- or 13-mer repeats of 8.3-12.5kDa, RiAFP is notable for containing only one disulfide bridge. This property of RiAFP makes it particularly attractive for recombinant expression and biotechnological applications. ==AFPs== AFPs work through an interaction with small ice crystals that is similar to an enzyme-ligand binding mechanism〔 which inhibits recrystallization of ice. This explanation of the interruption of the ice crystal structure by the AFP has come to be known as the ''adsorption-inhibition hypothesis''. According to this hypothesis, AFPs disrupt the thermodynamically favourable growth of an ice crystal via kinetic inhibition of contact between solid ice and liquid water. In this manner, the nucleation sites of the ice crystal lattice are blocked by the AFP, inhibiting the rapid growth of the crystal that could be fatal for the organism. In physical chemistry terms, the AFPs adsorbed onto the exposed ice crystal force the growth of the ice crystal in a convex fashion as the temperature drops,〔 which elevates the ice vapour pressure at the nucleation sites. Ice vapour pressure continues to increase until it reaches equilibrium with the surrounding solution (water), at which point the growth of the ice crystal stops. The aforementioned effect of AFPs on ice crystal nucleation is lost at the thermal hysteresis point. At a certain low temperature, the maximum convexity of the ice nucleation site is reached. Any further cooling will actually result in a "spreading" of the nucleation site away from this convex region, causing rapid, uncontrollable nucleation of the ice crystal.〔 The temperature at which this phenomenon occurs is the thermal hysteresis point. The ''adsorption-inhibition hypothesis'' is further supported by the observation that antifreeze activity increases with increasing AFP concentration – the more AFPs adsorb onto the forming ice crystal, the more 'crowded' these proteins become, making ice crystal nucleation less favourable. In the ''R. inquisitor'' beetle, AFPs are found in the haemolymph, a fluid that bathes all the cells of the beetle and fills a cavity called the haemocoel.〔 The presence of AFPs in ''R. inquisitor'' allows the tissues and fluids within the beetle to withstand freezing up to -30°C (the thermal hysteresis point for this AFP). This strategy provides an obvious survival benefit to these beetles, who are endemic to cold climates, such as Scandinavia, Siberia, and Alaska. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「RiAFP」の詳細全文を読む スポンサード リンク
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