Also acts, more slowly, on 2,5-diaminohexanoate forming 2-amino-5-oxohexanoate, which then cyclizes non-enzymically to 1-pyrroline-2-methyl-5-carboxylate. It has equal activity with NAD+ and NADP+ [cf. EC 1.4.1.26, 2,4-diaminopentanoate dehydrogenase (NAD+)].