Reaction catalyzed by N4-bis(aminopropyl)spermidine synthase (2.5.1.128)

2		+			=	2		+
	2 S-adenosyl 3-(methylsulfanyl)propylamine	+		spermidine	=		2 S-methyl-5'-thioadenosine	+		N4-bis(aminopropyl)spermidine