This enzymatic domain is part of bacterial polyketide synthases and catalyses the first step in the reductive modification of the beta-carbonyl centres in the growing polyketide chain. It uses NADPH to reduce the keto group to a hydroxy group [1].

1: Structural and stereochemical analysis of a modular polyketide synthase ketoreductase domain required for the generation of a cis-alkene. Bonnett SA, Whicher JR, Papireddy K, Florova G, Smith JL, Reynolds KA; Chem Biol. 2013;20:772-783. PMID:23790488