these reactions take place only under anaerobic conditions and require phosphate ( or arsenate ) , a reducing agent , diphosphothiamine , coenzyme a , an electron acceptor ( ferredoxin , flavins , dyes , or certain inorganic anions ) , and a divalent cation ( co ( ++ ) > mn ( ++ ) > mg ( ++ ) > fe ( ++ ) ) .
C0031603
phosphate
C0003075
anions