Major changes in complex I activity in mitochondria from aged rats may not be detected by direct assay of NADH:coenzyme Q reductase.
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.
Genova
M L
ML
Dipartimento di Biochimica G. Moruzzi, University of Bologna, Italy.
Castelluccio
C
C
Fato
R
R
Parenti Castelli
G
G
Merlo Pich
M
M
Formiggini
G
G
Bovina
C
C
Marchetti
M
M
Lenaz
G
G
D000375:Aging / Q000378:metabolism*; D000818:Animals; D004579:Electron Transport; D042967:Electron Transport Complex I; D007700:Kinetics; D008297:Male; D008929:Mitochondria, Heart / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000201:enzymology*; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000032:analysis* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014451:Ubiquinone / Q000378:metabolism
D014451:Ubiquinone; D009247:NADH, NADPH Oxidoreductases; D016660:NAD(P)H Dehydrogenase (Quinone); D042967:Electron Transport Complex I