Myelin basic protein‐specific protein methylase I activity in shiverer mutant mouse brain

Myelin basic protein (MBP)‐specific protein‐arginine N‐methyltransferase (protein methylase I) activity in homozygous shiverer (shi/shi) mutant mouse brain is significantly higher than in than normal littermate brain at the onset of myelination. While the enzyme activity (expressed as pmol os S‐adenosyl‐L‐[methyl‐¹⁴C] methelination used /min/mg enzyme protein) increase coincidently during the period of myelination in the normal brain (15–18 days of age), it decreases significantly in the mutant brain during this period of time. These results are in contrast to those found with another dysmyelinating mutant, jimpy (jp/Y) mice, in which the enzyme activity in the mutant brain is similar to that in the normal animals but remains unchanged during the myelination process. There is no difference in the weight and protein concentration of the normal and shiverer mutant brains with corresponding ages, and the histone‐specific portein methylase I activity is also unaffected in the shiverer brain.