Kinetics of the transhydrogenase reaction catalyzed by mitochondrial NADH:ubiquinone oxidoreductase (complex I) |
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Authors: | Zakharova N V |
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Institution: | (1) Department of Biochemistry, School of Biology, Lomonosov Moscow State University, Moscow, 119992, Russia |
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Abstract: | The kinetics of the NADH 3'-acetylpyridine adenine dinucleotide (APAD+) transhydrogenase reaction (DD-reaction) catalyzed by different preparations of mitochondrial NADH-dehydrogenase (submitochondrial particles (SMP), purified Complex I, and three-subunit fragment of Complex I (FP)) have been studied. Complex I (in SMP or in purified preparation) catalyzes two NADH APAD+ reactions with different rates and nucleotide affinities. Reaction 1 has high affinity to APAD+ (K
m = 7 M, for SMP) and low rate (V
m = 0.2 mol/min per mg protein, for SMP) and occurs with formation of a ternary complex. Reaction 2 has much higher rate and considerably lower affinity for oxidized nucleotide (V
m = 1.7 mol/min per mg protein and K
m = 160 M, for SMP). FP catalyzes only reaction 1. ADP-ribose inhibits reaction 1 with mixed type inhibition (competitive with non-competitive) with respect to NADH and APAD+. Rhein competes with both substrates. The results suggest that at least two nucleotide-binding sites exist in Complex I. |
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Keywords: | NADH:ubiquinone oxidoreductase transhydrogenase reaction kinetics Complex I submitochondrial particles three-subunit flavoprotein |
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