Fatty acid synthase alpha subunit; part of the gene cluster that mediates the biosynthesis of oryzines, natural products with an unusual maleidride backbone (PubMed:30104550). The two subunits of the fungal fatty acid synthase oryfasA and oryfasB probably form octenoic acid (Probable). This fatty acid is most likely activated by the acyl-CoA ligase oryP to give octenyl-CoA before the citrate synthase-like protein oryE catalyzes condensation with oxaloacetate to form tricarboxylic acid (Probable). The next steps of the pathways are conjectural, but a favorite possible route has been proposed, beginning with decarboxylation and concomitant dehydration by the decarboxylase oryM, followed by tautomerization, which may lead to the production of a diene intermediate (Probable). Reduction of this diene intermediate could give the known metabolite piliformic acid (Probable). On the pathway to oryzine B and oryzine A, however, hydroxylation of the diene by the alpha-ketoglutarate-dependent dioxygenase oryG and lactonisation by the lactonohydrolases oryH or oryL could give oryzine B directly (Probable). Finally, enoyl reduction by the dehydrogenase oryD would then convert oryzine B into oryzine A (Probable). acetyl-CoA + 2n H(+) + n malonyl-CoA + 2n NADPH = a long-chain fatty acyl-CoA + n CO2 + n CoA + H2O + 2n NADP(+) a fatty acyl-[ACP] + H(+) + malonyl-[ACP] = a 3-oxoacyl-[ACP] + CO2 + holo-[ACP] a (3R)-hydroxyacyl-[ACP] + NADP(+) = a 3-oxoacyl-[ACP] + H(+) + NADPH Secondary metabolite biosynthesis. Fatty acid synthase is composed of alpha and beta subunits. Belongs to the thiolase-like superfamily. Fungal fatty acid synthetase subunit alpha family.