Catalyses the reduction of malonate semialdehyde to 3-hydroxypropanoate, a key step in the 3-hydroxypropanoate and the 3-hydroxypropanoate/4-hydroxybutyrate cycles, autotrophic CO2 fixation pathways found in some green non-sulfur phototrophic bacteria and archaea, respectively [1,2]. The enzyme from Chloroflexus aurantiacus is bifunctional, and also catalyses the upstream reaction in the pathway, EC 1.2.1.75 [3]. Different from EC 1.1.1.59 [3-hydroxypropionate dehydrogenase (NAD+)] by cofactor preference.
