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At least 307 records · Page 17Linked to original sources
PubMed1996

Novel difference in IF1 reactivity to Zn2+ in rabbit versus rat cardiomyocytes, mitochondria, and submitochondrial particles.

Zn2+ has a paradoxical effect on IF1-ATPase interaction in cardiac muscle mitochondria in so-called slow heart-rate mammalian species like rabbit. In such slow heart-rate mammalian species, it completely prevents IF1-mediated ATPase inhibition regardless of pH while concomitantly causing full IF1 binding to the ATPase, again, regardless of pH (Rouslin et al. (1993) J. Bioenerget. Biomembr. 25, 297-306). While our earlier study suggested that there are two kinds of IF1-ATPase interaction, a docking interaction and an ATPase inhibitory interaction with Zn2+ promoting docking and interfering with inhibition, it did not yield information on whether Zn2+ interacted primarily with IF1, with the ATPase, or with both. In the present study we show that, in contrast to its effects in rabbit cardiomyocytes, mitochondria, and SMP in which Zn2+ fully blocked IF1-mediated ATPase inhibition, Zn2+ actually enhanced ATPase inhibition in rat cardiomyocytes, although the extent of this effect was limited by the low level of IF1 in rat cardiomyocytes. Moreover, Zn2+ had no effect on IF1-mediated ATPase inhibition in rat heart mitochondria and, as suggested by inter and intra-species IF1 binding to SMP, the different effects of Zn2+ in rabbit versus those in rat appear to be mediated primarily through the different reactivities of rabbit and rat IF1 to Zn2+.

Animals↗
PubMed1996

Oxidative modification of nicotinamide nucleotide transhydrogenase in submitochondrial particles: effect of endogenous ubiquinol.

The present paper describes the sensitivity of the mitochondrial nicotinamide nucleotide transhydrogenase (EC 1.6.1.1) to oxidative modification, and the effects of endogenous ubiquinol on this modification. A comparison is made between the effects of treatment with ADP-Fe3+ and ascorbate and with peroxynitrite, using kinetic, electrophoretic, and immunological analyses, together with lipid peroxidation measurements. The transhydrogenase was inactivated by both types of oxidative modification, but apparently through different mechanisms. Ubiquinol protected the enzyme against inactivation only when the modification was caused by ADP-Fe3+ and ascorbate treatment. Kinetic measurements revealed a threefold increase of the Km value of the enzyme for NADPH after exposure to ADP-Fe3+ and ascorbate, and a twofold increase of the Km values for both NADH and NADPH after exposure to peroxynitrite. NAD(H) exerted a protection against trans-hydrogenase inactivation when added to the preincubation in the case of peroxynitrite, but neither NAD(H) or NADP(H) protected in the case of ADP-Fe3+ and ascorbate. Using immunoblotting it was shown that the enzyme became both aggregated and fragmented, although to different extents, depending on the oxidative system used. Again, ubiquinol prevented these effects only in the case of ADP-Fe3+ and ascorbate treatment. Furthermore, there occurred a striking decrease in the 66-kDa trypsin fragment after exposure of the enzyme to ADP-Fe3+ and ascorbate, and of the 48-kDa trypsin fragment after exposure to peroxynitrite. It is concluded that the mitochondrial nicotinamide nucleotide transhydrogenase is sensitive to oxidative stress and that the mechanism underlying this can vary according to the challenge to which the enzyme is exposed. Endogenous ubiquinol may play a role in protecting the enzyme against agents perturbing the lipid phase of the membrane.

Adenosine Diphosphate↗
PubMed1978

The orientation of a heme of cytochrome c oxidase in submitochondrial particles.

The electron paramagnetic resonance of the low spin signal from oxidized cytochrome c oxidase has been studied in oreinted multilayers of submitochondrial and electron transport particles. Measurements of the angular variation of the EPR spectra with the multilayer plane orientation allow the determination of the heme orientation in the multilayer. The heme normal lies in the membrane plane and the y-axis of the heme makes an angle of 30 degrees with the membrane normal. Analysis of the line shape reveals the presence of mosaic spread in the multilayer almost half of which is attributable to deviations of protein orientation within the membrane.

Animals↗
PubMed1992

The effect of delta mu H+ on the interaction of rotenone with complex I of submitochondrial particles.

The inhibition by rotenone of the forward (NADH-oxidase) and reverse (delta mu H(+)-dependent succinate-NAD+ reductase activities of submitochondrial vesicles was measured. The inhibition of NADH-oxidase, measured in the presence of uncoupler, followed a monophasic inhibition curve with Ki < or = 2 nM. The reverse electron flow was only partially (40%) inhibited at these rotenone concentrations. The rest of the activity was less sensitive to the inhibitor (Ki approximately 30 nM). The lower affinity for the inhibitor of the reverse electron flow is a consequence of enhanced rate of rotenone dissociation caused by the high delta mu H+ value required for this reaction. The analysis of the results indicates that the AS-SMP preparation consists of two subpopulations: one with a relatively low degree of coupling, which exhibits high sensitivity to rotenone and the other which is highly coupled with lower affinity to the inhibitor.

Mitochondria↗
PubMed1975

The effects of ADP on reverse electron flow and the oxygen exchange reactions catalyzed by bovine heart muscle submitochondrial particles.

1,N6-Ethenoadenosine diphosphate (epsilon-ADP) inhibits reverse electron flow (succinate leads to NAD+ driven by ATP) by competing with ATP, in contrast to ADP which we have shown previously to be a noncompetitive inhibitor. From these and other data it is concluded that the noncompetitive inhibition noted with ADP results from a combination of competitive inhibition plus non- or uncompetitive inhibition, the former occurring at a relatively nonspecific catalytic site and the latter at an extracatalytic site apparently quite specific for ADP. ADP, which stimulates ATP in equilibrium H2O and Pi in equilibrium H2O exchanges appears to be necessary for inhibition by arsenate of these exchanges. It is suggested that the ATP-supported Pi in equilibrium H2O exchange may be predominantly of the medium or intermediate type, depending on the concentrations of the Mg2+ complexes of ADP and Pi. Thus only exchanges involving medium ADP and Pi would be expected to show arsenate sensitivity.

Adenosine Diphosphate↗