Extraction of rat myelin basic protein free of other basic proteins of whole central nervous system tissue. An analysis of its electrophoretic heterogeneity.

Extracts of subcellular fractions isolated from rat brain homogenates were obtained by treatment of the lyophilized preparations with 0.1 N HCl. When the extracts were analyzed by polyacrylamide gel electrophoresis, the only ones found to contain significant amounts of highly basic proteins were those of myelin and nuclei. The electrophoretic patterns of highly basic proteins from nuclei resembled those of calf thymus histones, whereas the patterns of the highly basic protein obtained from myelin appeared to be unique. Highly basic protein, electrophoretically identical with that extracted from isolated myelin, was also obtained from whole tissue. It was extracted from whole rat spinal cord and brain initially treated with chloroform-methanol by subsequent treatment with dilute acid at pH 3.0. At this pH, no highly basic proteins were extracted from similarly treated whole rat liver. Thus, the myelin basic protein can be obtained free of non-myelin basic proteins merely by controlling the pH of of the extraction. Subsequent treatment of both liver and brain with 0.1 N HCl removed additional basic proteins which were electrophoretically identical with those extracted from isolated brain nuclei. The present study confirms earlier observations that rat myelin basic protein consists of multiple electrophoretic forms. The additional data presented support the conclusion that the multiple forms are not artifacts attributable either to the conditions of extraction or the conditions of electrophoresis. The electrophoretic heterogeneity of rat myelin basic protein is considerably greater than that which has been observed in myelin basic protein of other species.