Immunochemical evidence of phosphorylation of a new 23K basic protein in rat brain myelin

Myelin from developing rat brain (8–44 day-old rat) was incubated in vitro with -³²P]ATP to determine how many basic proteins were phosphorylated. Myelin proteins were separated by polyacrylamide gel electrophoresis and transferred to nitrocellulose sheets. The nitrocellulose sheets were stained with antisera to human basic protein by the immunoblot technique. Five basic proteins with molecular weights of 23K, 21.5K, 18.5K, 17K, and 14K were distinctly immunostained. These basic proteins were found to be phosphorylated when the same nitrocellulose sheets were exposed to x-ray film. The in vitro phosphorylation of 23K and 21.5K basic proteins appear to decrease with maturation of the brain. The result of this study suggests that intense phosphorylation of various forms of basic proteins, in particular 23K and 21.5K basic proteins, during the initial stages of myelin formation, may play a pivotal role in the compaction of myelin membrane.