Description
The reaction of this enzyme occurs in three steps, with some of the intermediates presumably remaining enzyme-bound: (a) NAD+-dependent dehydrogenation of spermidine, (b) transfer of the 4-aminobutylidene group from dehydrospermidine to putrescine and (c) reduction of the imine intermediate to form homospermidine. This enzyme is more specific than EC 2.5.1.44, homospermidine synthase, which is found in bacteria, as it cannot use putrescine as donor of the 4-aminobutyl group. Forms part of the biosynthetic pathway of the poisonous pyrrolizidine alkaloids of the ragworts (Senecio)