Irreversible Random Adsorption Inhibition Model For Thermal Hysteresis Activity Of Antifreeze Proteins

Some organisms that survive in cold environments can synthesize proteins with special function.The proteins,called antifreeze proteins(AFPs),can inhibit the growth of ice crystals and lower the freezing point of the solution in a non-colligative manner,thereby preventing cells from being destroyed by freezing.The difference value between the melting point and freezing point is called thermal hysteresis(TH).Antifreeze property of antifreeze protein makes it have excellent application prospects in the fields of cryopreservation,cryomedicine and antifreeze materials.Some experimental studies have found that antifreeze proteins in solution are adsorbed on the surface of ice crystals to inhibit the growth of ice crystals.But there is no theoretical research for the changes in the accumulation of antifreeze proteins on the surface of ice crystals and their effects on thermal hysteresis.According to the adsorption inhibition theory,considering the spatial structure characteristics of antifreeze protein molecules and the binding specificity of AFPs to surface of ice crystals,an irreversible random adsorption inhibition model of AFPs was established.The adsorption and accumulation of antifreeze glycoprotein(AFGP)on the surface of ice crystals has been analyzed.The change of coverage rate for antifreeze glycoprotein on surface of ice crystals with time was explained.Thermal hysteresis activities of antifreeze glycoprotein under different concentrations with same accumulation time were obtained.The theoretical calculation results are basically consistent with the experimental results..Tenebrio molitor Antifreeze Protein(Tm AFP)is a kind of highly active Antifreeze Protein derived from insects.Fluorescent protein labeling experiments showed that Tm AFP could bind irreversibly on both the base and prismatic plane of ice crystal.Considering the polycrystalline surface adsorption characteristics of Tm AFP on ice crystals,the basic irreversible dynamic random adsorption inhibition model was extended to the polycrystalline surface irreversible random adsorption inhibition model to describe the adsorption process of Tm AFP on ice crystals.The effects of Tm AFP solution con-centration and the coverage area of single Tm AFP molecule on the ice surface to thermal hysteresis activity were calculated and analyzed.The time dependence and concentration dependence of Tm AFP thermal hysteresis activity were also calculated.The theoretical results are in good agreement with the experimental data,which provides a theoretical basis for understanding the concentration dependence of thermal hysteresis activity under irreversible adsorption conditions of antifreeze proteins.The type Ⅲ fish antifreeze protein(AFPⅢ)is a kind of moderately active antifreeze protein.Experimental studies have found that AFPIII can irreversibly bind to ice crystal surface specifically,and its thermal hysteresis activity is obviously different under different ambient temperature and cooling rate.On the basis of the basic model,the irreversible adsorption model was established to describe the adsorption and accumulation process of AFPⅢs on the ice crystal surface,considering the factors of water molecules competing for binding sites on the ice crystal surface.The influence of molecular size of AFPⅢ,solution concentration,ambient temperature and cooling rate on the coverage and thermal hysteresis activity of AFPⅢ on ice crystal surface was discussed.The theoretical calculation results are in good agreement with the experimental results,which gives a reasonable explanation for the complex thermal hysteresis phenomenon of AFPⅢ in the experiment.