C-8 sterol isomerase; part of the third module of ergosterol biosynthesis pathway that includes the late steps of the pathway (By similarity). ERG2 catalyzes the reaction which results in unsaturation at C-7 in the B ring of sterols and thus converts fecosterol to episterol (By similarity). The third module or late pathway involves the ergosterol synthesis itself through consecutive reactions that mainly occur in the endoplasmic reticulum (ER) membrane. Firstly, the squalene synthase ERG9 catalyzes the condensation of 2 farnesyl pyrophosphate moieties to form squalene, which is the precursor of all steroids. Squalene synthase is crucial for balancing the incorporation of farnesyl diphosphate (FPP) into sterol and nonsterol isoprene synthesis. Secondly, squalene is converted into lanosterol by the consecutive action of the squalene epoxidase ERG1 and the lanosterol synthase ERG7. Then, the delta(24)-sterol C-methyltransferase ERG6 methylates lanosterol at C-24 to produce eburicol. Eburicol is the substrate of the sterol 14-alpha demethylase encoded by CYP51A, CYP51B and CYP51C, to yield 4,4,24-trimethyl ergosta-8,14,24(28)-trienol. CYP51B encodes the enzyme primarily responsible for sterol 14-alpha-demethylation, and plays an essential role in ascospore formation. CYP51A encodes an additional sterol 14-alpha-demethylase, induced on ergosterol depletion and responsible for the intrinsic variation in azole sensitivity. The third CYP51 isoform, CYP51C, does not encode a sterol 14-alpha-demethylase, but is required for full virulence on host wheat ears. The C-14 reductase ERG24 then reduces the C14=C15 double bond which leads to 4,4-dimethylfecosterol. A sequence of further demethylations at C-4, involving the C-4 demethylation complex containing the C-4 methylsterol oxidases ERG25, the sterol-4-alpha-carboxylate 3-dehydrogenase ERG26 and the 3-keto-steroid reductase ERG27, leads to the production of fecosterol via 4-methylfecosterol. ERG28 has a role as a scaffold to help anchor ERG25, ERG26 and ERG27 to the endoplasmic reticulum. The C-8 sterol isomerase ERG2 then catalyzes the reaction which results in unsaturation at C-7 in the B ring of sterols and thus converts fecosterol to episterol. The sterol-C5-desaturases ERG3A and ERG3BB then catalyze the introduction of a C-5 double bond in the B ring to produce 5-dehydroepisterol. The C-22 sterol desaturases ERG5A and ERG5B further convert 5-dehydroepisterol into ergosta-5,7,22,24(28)-tetraen-3beta-ol by forming the C-22(23) double bond in the sterol side chain. Finally, ergosta-5,7,22,24(28)-tetraen-3beta-ol is substrate of the C-24(28) sterol reductase ERG4 to produce ergosterol (Probable). fecosterol = episterol Steroid metabolism; ergosterol biosynthesis. Expression is increased in the absence of the C-24(28) sterol reductase ERG4. Surprisingly, does not show changed sensitivity to amines and does not lead to depletion of ergosterol. In Fusarium, the biosynthesis pathway of the sterol precursors leading to the prevalent sterol ergosterol differs from yeast. The ringsystem of lanosterol in S.cerevisiae is firstly demethylised in three enzymatic steps leading to the intermediate zymosterol and secondly a methyl group is added to zymosterol by the sterol 24-C-methyltransferase to form fecosterol. In Fusarium, lanosterol is firstly transmethylated by the sterol 24-C-methyltransferase leading to the intermediate eburicol and secondly demethylated in three steps to form fecosterol. Belongs to the ERG2 family.