Reaction catalyzed by GDP-Man:Man3GlcNAc2-PP-dolichol alpha-1,2-mannosyltransferase (2.4.1.131)

2		+			=	2		+
	2 GDP-alpha-D-mannose	+		D-Man-alpha-(1->3)-(D-Man-alpha-(1->6))-D-Man-beta-(1->4)-D-GlcNAc-beta-(1->4)-D-GlcNAc-diphosphodolichol	=		2 UDP	+		D-Man-alpha-(1->2)-D-Man-alpha-(1->2)-D-Man-alpha-(1->3)-(D-Man-alpha-(1->6))-D-Man-beta-(1->4)-D-GlcNAc-beta-(1->4)-D-GlcNAc-diphosphodolichol