Microheterogeneity of guinea pig myelin basic protein.

Organ-specific highly basic protein derived from guinea pig central nervous system myelin was found to be electrophoretically heterogeneous. It did not appear to be heterogeneous with respect to molecular size. The electrophoretic technique used to demonstrate this heterogeneity was capable of resolving mixtures of closely related basic proteins whether they were present in crude extracts or in relatively pure preparations. Multiple forms of this basic protein were present in extracts obtained from whole tissue under conditions designed to minimize artifactitious changes as well as in a purified basic protein obtained directly from isolated myelin. This observation suggested that multiple forms may exist in situ. Analyses of various acid extracts of brain and liver by the same electrophoretic technique provided evidence that myelin basic protein was the only highly basic protein specific to brain which was present in significant amounts in these extracts. Extracts prepared from brain with 0.1 M acetic acid contained myelin basic protein free of other highly basic proteins.