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. 1995 Oct 1;311 ( Pt 1)(Pt 1):105-9.
doi: 10.1042/bj3110105.

Major changes in complex I activity in mitochondria from aged rats may not be detected by direct assay of NADH:coenzyme Q reductase

M L Genova  1 , C Castelluccio, R Fato, G Parenti Castelli, M Merlo Pich, G Formiggini, C Bovina, M Marchetti, G Lenaz
Affiliations

Major changes in complex I activity in mitochondria from aged rats may not be detected by direct assay of NADH:coenzyme Q reductase

M L Genova et al. Biochem J. .

Abstract

We have investigated the respiratory activities and the concentrations of respiratory chain components of mitochondria isolated from the livers and hearts of two groups of rats aged 6 and 24 months respectively. In comparison with the adult controls (6 months), in aged rats there was a decline in total aerobic NADH oxidation in both tissues; only minor (non-significant) changes, however, were found in NADH:coenzyme Q reductase and cytochrome oxidase activities, and there was no change in ubiquinol-cytochrome c reductase activity. The coenzyme Q levels were slightly decreased in mitochondria from both organs of aged rats. The lowered NADH oxidase activity is not due to the slight decrease observed in the coenzyme Q levels, but is the result of decreased Complex I activity. Since the assay of NADH:coenzyme Q reductase requires quinone analogues, none of which can evoke its maximal turnover [Estornell, Fato, Pallotti and Lenaz (1993) FEBS Lett. 332, 127-131], its activity has been calculated indirectly by taking advantage of the relationship that exists between NADH oxidation and ubiquinol oxidation through the coenzyme Q pool. The results, expressed in this way, show a drastic loss of activity of Complex I in both the heart and the liver of aged animals in comparison with adult controls.

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