S-adenosyl 3-(methylsulfanyl)propylamine + spermidine => N(4)-aminopropylspermidine + S-methyl-5'-thioadenosine + H(+)
s-adenosyl 3-(methylsulfanyl)propylamine + spermidine => n(4)-aminopropylspermidine + s-methyl-5'-thioadenosine + h(+)