Hydrophobic interaction and a model for the elasticity of elastin.

Abstract

AbstractThe thermodynamics of the elastic process in the rubberlike protein elastin have been investigated by microcalorimetery. The results indicate that the reversible heat liberated upon the extension of water‐swollen elastin at room temperature is much largerthan the stored elastic energy, indicating a large than the stored elastic energy, indicating a large, negative internal energy change for stretching. The ratio of the measured internal energy change to the stored energy varies inversely wiht extension, and at 22° C it is −91 for 2% extension and −3 for 70% extension. The interanl energy change also varies dramatically with temperature over the range of 2–65° C it is zero.The temperature dependence for internal energy change is virtually identical to the temperature dependence for internal energy changes associated with the breaking of hydrophobic interactions, and it is suggested that the measured internal energy change can be attributed entirely to hte absorption of water onto nonpolar groups in the elastin network. Calculatons based on this assumption indicate that the free‐energy change associated with this solvent–polymer process is large and positive. It is concluded that the absorption of water onto hydrophobic groups contributes to the elasticity of elastin, particularly at extensions of less than about 70%. The implications of this elastic mechanism are discussed in terms of the random‐network model for elastin structure.