Improving the quality of protein crystals through purification by isoelectric focusing.

Preparative flat-bed gel isoelectric focusing has reduced or eliminated observed heterogeneity in three different proteins, thereby greatly improving the quality of crystals grown from each of them. This improvement is manifested both in crystal size and in increased measurability of diffraction data. Isoelectric focusing is a general and nondestructive technique that may facilitate the crystallographic study of proteins which are biologically interesting, but which, for reasons of microheterogeneity, do not yield diffraction quality crystals.