title: Mechanism of ATP-driven electron transfer catalyzed by the benzene ring-reducing enzyme benzoyl-CoA reductase.
abstract: Benzoyl-CoA reductase (BCR) from the bacterium Thauera aromatica catalyzes the two-electron reduction of benzoyl-CoA (BCoA) to a nonaromatic cyclic diene. In a process analogous to enzymatic nitrogen reduction, BCR couples the electron transfer to the aromatic ring to a stoichiometric hydrolysis of 2 ATP/2e(-). Reduced but not oxidized BCR hydrolyzes ATP to ADP. In this work, purified BCR was shown to catalyze an isotope exchange from [(14)C]ADP to [(14)C]ATP, which was approximately 15% of the ATPase activity in the presence of equimolar amounts of ADP and ATP. In accordance, BCR (alpha beta gamma delta-composition) autophosphorylated its gamma-subunit when incubated with [gamma-(32)P]ATP. Formation of the enzyme-phosphate was independent of the redox state, whereas only dithionite-reduced BCR catalyzed a dephosphorylation associated with the ATPase activity. This finding suggests that the ATPase- and autophosphatase-partial activities of BCR exhibit identical redox dependencies. BCoA or the nonphysiological electron-accepting substrate hydroxylamine stimulated the redox-dependent effects; the rates of both the overall ATPase and the autophosphatase activities of reduced BCR were increased 6-fold. In contrast, BCoA and hydroxylamine had no effect on oxidized and phosphorylated BCR. The reactivity of the phosphoamino acid fits best with a phosphoamidate or acylphosphate linkage. The results obtained suggest a mechanism of ATP hydrolysis-driven electron transfer, which differs from that of nitrogenase by the transient formation of a phosphorylated enzyme.
authors.affiliation: Mikrobiologie, Fakultät für Biologie, Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Unciuleac
authors.forename: M
authors.initials: M
authors.lastname: Boll
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001554:Benzene; D002250:Carbon Radioisotopes; D002384:Catalysis; D004583:Electrons; D007553:Isotope Labeling; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D013379:Substrate Specificity; D020628:Thauera / Q000201:enzymology
chemical_list: D002250:Carbon Radioisotopes; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C109030:benzoyl-coenzyme A reductase (dearomatizing); D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases; D000251:Adenosine Triphosphatases; D001554:Benzene