Beta chain of the formate dehydrogenase (FDH) that catalyzes the reversible two-electron oxidation of formate to carbon dioxide. The beta chain is an electron transfer unit. Binds 3 [4Fe-4S] clusters. Measurements have been done with the heterotrimer complex. kcat is 262 sec(-1) with formate as substrate (at pH 7.6). Optimum pH is 9.5. Optimum temperature is 51 degrees Celsius. Heterotrimer of cytochrome c3 FDH2C and formate dehydrogenase FDH2 alpha and beta subunits that forms the FdhABC(3) complex. The trimeric FdhABC(3) complex is the main formate dehydrogenase enzyme in the presence of molybdenum.