Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.12.7.2 (hydrogenase)
 3,522 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Oxidative modification of nicotinamide nucleotide transhydrogenase in submitochondrial particles: effect of endogenous ubiquinol. 895 Oct 41

Mitochondria isolated from potato (Solanum tuberosum L.) tuber were investigated for the presence of a nicotinamide nucleotide transhydrogenase activity. Submitochondrial particles derived from these mitochondria by sonication catalyzed a reduction of NAD(+) or 3-acetylpyridine-NAD(+) by NADPH, which showed a maximum of about 50 to 150 nanomoles/minute.milligram protein at pH 5 to 6. The K(m) values for 3-acetylpyridine-NAD(+) and NADPH were about 24 and 55 micromolar, respectively. Intact mitochondria showed a negligible activity in the absence of detergents. However, in the presence of detergents the specific activity approached about 30% of that seen with submitochondrial particles. The potato mitochondria transhydrogenase activity was sensitive to trypsin and phenylarsine oxide, both agents that are known to inhibit the mammalian transhydrogenase. Antibodies raised against rat liver transhydrogenase crossreacted with two peptides in potato tuber mitochondrial membranes with a molecular mass of 100 to 115 kilodaltons. The observed transhydrogenase activities may be due to an unspecific activity of dehydrogenases and/or to a genuine transhydrogenase. The activity contributions by NADH dehydrogenases and transhydrogenase to the total transhydrogenase activity were investigated by determining their relative sensitivities to trypsin. It is concluded that, at high or neutral pH, the observed transhydrogenase activity in potato tuber submitochondrial particles is due to the presence of a genuine and specific high molecular weight transhydrogenase. At low pH an unspecific reaction of an NADH dehydrogenase with NADPH contributes to the total trans-hydrogenase activity.
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PMID:On the presence of a nicotinamide nucleotide transhydrogenase in mitochondria from potato tuber. 1666 99