title: Studies on the NADH-menaquinone oxidoreductase segment of the respiratory chain in Thermus thermophilus HB-8.
abstract: Five distinct low potential iron-sulfur clusters have been identified potentiometrically in the membrane particles from Thermus thermophilus HB-8. Three of these clusters (designated as [N-1H]T, [N-2H]T, and [N-3]T) exhibit the following midpoint redox potentials and g values (Em8.0 = -274 mV, gx,y,z = 1.93, 1.94, 2.02), (Em8.0 = -304 mV, gx,y,z = 1.89, 1.95, 2.04), and (Em8.0 = -289 mV, gx,y,z = 1.80, 1.83, 2.06), respectively. These clusters, one binuclear and two tetranuclear, have been shown to be components of the energy coupled NADH-menaquinone oxidoreductase complex (NADH dh I). They are reducible by NADH in the piericidin A-inhibited aerobic membrane particles as well as in the purified NADH dh I complex. Two additional very low potential iron-sulfur clusters (one binuclear, [N-1L]T, and one tetranuclear, [N-2L]T) were observed in membrane particles. These clusters possess the following physiochemical properties (Em8.0 = -418 mV, gx,y,z = 1.93, 19.5, 2.02) and (Em8.0 = -437 mV, gx,y,z = 1.89, 1.95, 2.04), respectively. No high potential tetranuclear cluster equivalent to the mitochondrial iron-sulfur cluster [N-2]B was found in this bacterial system. In membrane particles isolated from T. thermophilus HB-8 cells, four different semiquinone species have been identified based on their redox midpoint potentials [Em9(Q/QH2) = 40, -100, -160, -300 mV] and sensitivity to the quinone analogue inhibitor, 2-heptyl-4-hydroxy quinoline-N-oxide. Of these semiquinone species the -100 mV component has been suggested to be part of the NADH dehydrogenase. Piericidin A sensitive delta psi formation has been demonstrated to be coupled to the NADH-MQ1 oxidoreductase in membrane vesicles of T. thermophilus HB-8.
authors: Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104.
authors: S W
authors: SW
authors: Meinhardt
authors: D C
authors: DC
authors: Wang
authors: K
authors: K
authors: Hon-nami
authors: T
authors: T
authors: Yagi
authors: T
authors: T
authors: Oshima
authors: T
authors: T
authors: Ohnishi
mesh_terms: D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005609:Free Radicals; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D008564:Membrane Potentials; D008667:Metalloproteins / Q000378:metabolism*; D010084:Oxidation-Reduction; D011725:Pyridines / Q000494:pharmacology; D011808:Quinone Reductases / Q000378:metabolism*; D011809:Quinones; D013824:Thermus / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D005609:Free Radicals; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D011725:Pyridines; D011809:Quinones; C100213:piericidin A; D011808:Quinone Reductases