Adenylate-forming reductase, a natural product biosynthesis enzyme that resembles non-ribosomal peptide synthetases, yet serves to modify one substrate, rather than to condense two or more building blocks. The A-domain preferentially accepts L-serine, L-alanine and L-valine as substrates. The natural product of the enzyme is not yet known. Contains three distinct domains: an adenylation (A) domain that activates the substrate amino acid which is subsequently covalently linked as a thioester (aminoacyl-S-PCP) to the 4'-phosphopantetheine prosthetic group of the second domain, the peptidyl carrier protein (PCP) domain, as well as a reductase (R) domain of the ferredoxin-NADP reductase (FNR) type. Belongs to the adenylate-forming reductase family. Extended N-terminus.