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

	clathrin heavy chain-bound gamma-glutamine	+			=		clathrin heavy chain N5-methylglutamine	+		NH3
	clathrin heavy chain-bound gamma-glutamine	+		methylamine	=		clathrin heavy chain N5-methylglutamine	+		NH3