Fatty acid synthase beta 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(+) acetyl-CoA + holo-[ACP] = acetyl-[ACP] + CoA holo-[ACP] + malonyl-CoA = CoA + malonyl-[ACP] a (3R)-hydroxyacyl-[ACP] = a (2E)-enoyl-[ACP] + H2O a 2,3-saturated acyl-[ACP] + NAD(+) = a (2E)-enoyl-[ACP] + H(+) + NADH (9Z)-octadecenoyl-[ACP] + H2O = (9Z)-octadecenoate + H(+) + holo-[ACP] Secondary metabolite biosynthesis. [Alpha(6)beta(6)] hexamers of two multifunctional subunits (alpha and beta). Belongs to the fungal fatty acid synthetase subunit beta family.