Thermodynamic examination of the ordering of lipid hydrocarbon chains in the presence of protein

Thermodynamic relationships have been derived to describe the change in the entropy (Δ S ) of lipid vesicles in the presence of a protein in terms of experimental quantities, the concentration of protein (C), the temperature ( t m ), and the enthalpy (Δ H ) of the main lipid phase transition. Knowledge of the change in Δ S can provide an insight into the effect of a protein on the ordering of the lipid hydrocarbon chains. For a general case, evaluation of the entropy change requires information on the changes of Δ H and t m with respect to C . In a special cae where t m remains inchanged and (Δ H ) varies, the change in Δ S can be represented simply as (Δ H c − Δ H o )/ T m , where the subscripts c and o denote the presence and absence of a protein, respectively. Data for 1,2‐dimyristoyl phosphatidylcholone in the presence of lysozyme was used to illustrate a thermodynamic analysis.