Protein methylases during the development of rat brain

Abstract

Various protein methylases ( S-adenosylmethionine : protein methyltransferases) are evenly distributed in the cerebrum of rat. Protein methylase I and II are cytosolic and protein methylase III is nuclear bound. A substantial amount of protein methylase I was also found in the synaptosome. While the amount and the rate of precursor incorporation of protein in rat brain increased during the early phase of life, the amount and the rate of radioactive precursor incorporation of DNA and RNA gradually decreased. The amount of protein methylase I ( S-adenosylmethionine : protein arginine methyltransferase) per cell or in the total brain increases after birth until 10 days of life, and thereafter remains unchanged. Protein methylase III activity ( S-adenosylmethionine : protein-lysine methyltransferase) also increases until 10 days after birth, however, it decreases significantly thereafter. Contrary to the above two enzymes, protein methylase II activity ( S-adenosylmethionine : protein carboxyl methyltransferase) increases continually until puberty. Since myelination begins at about 10 days after birth in rat, and degenerative mutant jimpy mice contain normal amounts of the protein methylases, the above result suggests that methylation of protein in the brain might not be related to the formation of myelin.