the methylation of either methionine or arginine residues by enzyme i and ii , respectively , lowers the isoelectric point ( pi ) of cytochrome c : 9.23 , 9.33 , and 10.06 for s-methylmethionine- , ng-monomethylarginine-modified , and unmodified cytochrome c , respectively .
C0025646
methionine
C0042889
methylmethionine