Trans-enoyl reductase; part of the gene cluster that mediates the biosynthesis of aspyridones (PubMed:17369821, PubMed:20828130, Ref.5). The polyketide-amino acid backbone preaspyridone A is first assembled by the PKS-NRPS hybrid apdA (PubMed:17369821, PubMed:20828130). The assembly of preaspyridone A is initiated by loading of malonyl-CoA onto apdA, followed by decarboxylation to yield the acetyl starter unit (PubMed:20828130). The growing polyketide chain then elongates into a tetraketide (PubMed:20828130). The adpA PKS module catalyzes three Claisen condensations, as well as beta-keto processing and methylation (PubMed:17369821, PubMed:20828130). Alpha-methylation step during polyketide synthesis is a prerequisite and a key checkpoint for chain transfer between PKS and NRPS modules (PubMed:25494235). The downstream NRPS module contains the condensation (C), adenylation (A), and thiolation (T) domains and catalyzes the incorporation of tyrosine via the formation of the L-tyrosinyl-thioester and the amide linkage between L-tyrosinyl-thioester and the tetraketide (PubMed:20828130). The bimodular assembly line is terminated with a reductase (R) domain that facilitates formation and release of the tetramic acid product (PubMed:20828130). Because apdA lacks a designated enoylreductase (ER) domain, the required activity is provided the enoyl reductase apdC (PubMed:17369821, PubMed:20828130, Ref.5). ApdC appears to operate with different stereoselectivity in different PKS cycle (Ref.5). Combined with apdC, apdA is proposed to synthesize preaspyridone A via about 20 enzymatic steps (PubMed:20828130). A number of oxidative steps performed successively by the cytochrome P450 monooxygenases apdE and apdB are required for the conversion of preaspyridone A to aspyridone A (PubMed:17369821). The cytochrome P450 monooxygenase apdE is responsible for the oxidative dephenylation of preaspyridone A (Ref.5). Finally, the predicted FAD-dependent monooxygenase apdD and the acyl-CoA dehydrogenase apdG may be involved in the transformation of aspyridone A into aspyridone B (PubMed:17369821) (Probable). Secondary metabolite biosynthesis. Monomer. Expression is positively regulated by the aspyridones cluster specific transcription regulator apdR (PubMed:17369821). Belongs to the zinc-containing alcohol dehydrogenase family.