Involved in aliphatic epoxide carboxylation (PubMed:10411892, PubMed:9150202). Catalyzes the reductive cleavage of the thioether bond of 2-oxopropyl-coenzyme M (2-KPC), and the subsequent carboxylation of the ketopropyl cleavage product, yielding the products acetoacetate and free coenzyme M (PubMed:10411892). acetoacetate + coenzyme M + NADP(+) = 2-oxopropyl-coenzyme M + CO2 + NADPH Binds 1 FAD per subunit. Inhibited (at 40%) by the coenzyme M analog 2-bromoethanesulfonate (BES). BES is a time-dependent inactivator of dithiothreitol-reduced 2-KPCC, where the redox active cysteines are in the free thiol forms. BES does not inactivate air-oxidized 2-KPCC, where the redox active cysteine pair is in the disulfide form. BES specifically alkylates the interchange thiol that facilitates thioether bond cleavage and enolacetone formation during catalysis. Alkene metabolism; propylene degradation. Homodimer (PubMed:9150202, PubMed:12390015). Component II of the aliphatic epoxide carboxylation complex together with components I, III and IV (PubMed:9150202, PubMed:10411892). Contains three domains, the FAD binding domain, the NADPH binding domain, and the dimerization domain (PubMed:12390015). The binding of the substrate induces a conformational change that results in the sequestration of the substrate at the dimer interface (PubMed:12390015, PubMed:16388586). The active site is a redox-active disulfide bond (PubMed:12390015, PubMed:16388586). 2-KPC reduction and carboxylation assumes the formation of a mixed disulfide between the interchange thiol (Cys-82) and coenzyme M (PubMed:16388586). Belongs to the class-I pyridine nucleotide-disulfide oxidoreductase family.