Phase behavior of a simple model of globular proteins

A simple model of globular proteins which incorporates anisotropic attracti ons is proposed. It is closely related to models used to model simple hydro gen-bonding molecules such as water. Theories for both the fluid and solid phases are presented, and phase diagrams calculated. The model protein exhi bits a fluid-fluid transition which is metastable with respect to the fluid -solid transition for most values of the model parameters. This is behavior often observed for globular proteins. The model offers an explanation of t he difficulty observed in crystallizing some globular proteins and suggests that some proteins may not have a solid phase at all under all but extreme conditions. (C) 1999 American Institute of Physics. [S0021-9606(99)50234-1 ].