obsolete dimethylhistidine N-methyltransferase activity (obsolete GO:0030745)
OBSOLETE. Catalysis of the reaction: S-adenosyl-L-methionine + N-alpha,N-alpha-dimethyl-L-histidine = S-adenosyl-L-homocysteine + N-alpha,N-alpha,N-alpha-trimethyl-L-histidine.