REDOX CHEMISTRY OF COBALAMIN AND IRON-SULFUR COFACTORS IN THE TETRACHLOROETHENE REDUCTASE OF DEHALOBACTER-RESTRICTUS

Respiration of Dehalobacter restrictus is based on reductive dechlorin ation of tetrachloroethene. The terminal component of the respiratory chain is the membrane-bound tetrachloroethene reductase. The metal pro sthetic groups of the purified enzyme have been studied by optical and EPR spectrescopy, The 60-kDa monomer contains one cobalamin with E-m( Co1+/2+)= -350 mV and E-m(Co2+/3+) > 150 mV and two electron-transferr ing [4Fe-4S]((2+;1+)) clusters with rather low redox potentials of E-m = -480 mV. The cob(rr)alamin is present in the base-off configuration, A completely reduced enzyme sample reacted very rapidly with tetrachl oroethene yielding base-off cob(II)alamin rather than trichlorovinyl-c ob(III)alamin. (C) 1997 Federation of European Biochemical Societies.