Reaction catalyzed by protein-glutamine gamma-glutamyltransferase (2.3.2.13)

	H2A histone type 1-bound gamma-glutamine	+			=		H2A histone type 1 N5-methylglutamine	+		NH3
	H2A histone type 1-bound gamma-glutamine	+		methylamine	=		H2A histone type 1 N5-methylglutamine	+		NH3