2.5.1.44	2 putrescine = sym-homospermidine + NH3 + H+	the reaction mechanism emphasizes cation-Pi interaction through a conserved Trp residue as a key stabilizer of high energetic transition states. The enzyme has two distinct substrate binding sites, one of which is highly specific for putrescine. Enzyme HSS features a side pocket in the direct vicinity of the active site formed by conserved amino acids and a potential substrate discrimination, guiding, and sensing mechanism	739672	
2.5.1.44	2 putrescine = sym-homospermidine + NH3 + H+	the reaction of this enzyme occurs in three steps: i. NAD-dependent dehydrogenation of putrescine, ii. transfer of the 4-aminobutylidene group from dehydroputrescine to a second molecule of putrescine, iii. reduction of the imine intermediate to form homospermidine. Hence the overall reaction is transfer of a 4-aminobutyl group. In the presence of putrescine, spermidine can function as a donor of the aminobutyl group, in which case, propane-1,3-diamine is released instead of ammonia. Differs from EC 2.5.1.45, homospermidine synthase, spermidine-specific, which cannot use putrescine as donor of the aminobutyl group	-	
2.5.1.44	putrescine + spermidine = sym-homospermidine + propane-1,3-diamine	-	-	
2.5.1.44	putrescine + spermidine = sym-homospermidine + propane-1,3-diamine	the reaction mechanism emphasizes cation-Pi interaction through a conserved Trp residue as a key stabilizer of high energetic transition states. The enzyme has two distinct substrate binding sites, one of which is highly specific for putrescine. Enzyme HSS features a side pocket in the direct vicinity of the active site formed by conserved amino acids and a potential substrate discrimination, guiding, and sensing mechanism	739672