label: N-terminal N-methyl-glycyl-L-lysyl-L-glutamyl-[protein] + S-adenosyl-L-methionine => N-terminal N,N-dimethyl-glycyl-L-lysyl-L-glutamyl-[protein] + S-adenosyl-L-homocysteine + H(+)
label_lc: n-terminal n-methyl-glycyl-l-lysyl-l-glutamyl-[protein] + s-adenosyl-l-methionine => n-terminal n,n-dimethyl-glycyl-l-lysyl-l-glutamyl-[protein] + s-adenosyl-l-homocysteine + h(+)