Time dependence of the methylation of myelin basic protein from bovine brain; evidence for protein-methylarginine demethylation.

In the presence of excess S-adenosylmethionine (AdoMet), the extent of methylation of myelin basic protein (MBP) by partially purified AdoMet:MBP methyltransferase is a non-linear function of time, reaching a limiting value as available MBP is depleted and then decreasing monotonically. This decrease is not caused by proteolytic cleavage of MBP nor by effects related to substrate or product instability under the incubation conditions and is not observed in heat-inactivated samples. S-Adenosylhomocysteine is not required for the demethylation to occur, and with purified enzyme, the decrease is not observed. The data strongly suggest that the decrease in methyl content represents an enzyme-catalyzed demethylation reaction. This would represent the first report of an enzyme which catalyzes protein-methylarginine demethylation.