(179m) Derivation of Modified Langmuir Isotherm and Application to Antifreeze Protein Multimers

Antifreeze proteins (AFPs) are ice binding proteins found in various organisms allowing them to survive at subzero temperatures by inhibiting ice crystal growth. Upon lowering the solution temperature, AFPs cause thermal hysteresis, which is the difference between the freezing and melting temperatures and it is the common measure of their activity that can be experimentally determined. This interesting property has made them suitable candidates for several applications such as subzero preservation of cells, tissues, organs, frozen foods, and heat transfer fluids in refrigeration systems. These real life applications, however require a better understanding of their mechanism of action on the ice surface that would help to design superior molecules that are more suitable for economical use.

This study aims to better understand the equilibrium behavior of the AFP/ice system by the application of adsorption isotherms. An adsorption equilibrium model is derived based on the classical Langmuir isotherm in order to determine the surface concentration of the AFP molecules on the ice surface, which is experimentally impossible to determine. The link between thermal hysteresis and surface coverage was shown for the one-, two- and three-domain type III fish AFPs that were designed and expressed in E.Coli expression system. The equilibrium binding constant and hence the adsorption free energy for the type III AFP domain is also presented.