A protein, which is an aminoketone asymmetric reductase, having an effect of producing d-pseudoephedrine by acting on 1-2-methylaminopropiophenone, and having the following physiochemical properties: substrate: 1-2-methylaminopropiophenone optimum pH: pH 8.1 optimum temperature: 55.degree. C. coenzyme: NADP molecular weight: about 28500 Da homotetramer and a nucleic acid coding the protein.