Van den Bergen 1994 Eur J Biochem

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Van den Bergen CW, Wagner AM, Krab K, Moore AL (1994) The relationship between electron flux and the redox poise of the quinone pool in plant mitochondria. Interplay between quinol-oxidizing and quinone-reducing pathways. Eur J Biochem 226:1071-8.

» PMID: 7813462 Open Access

Van den Bergen Corinne W, Wagner Anneke M, Krab Klaas, Moore Anthony L (1994) Eur J Biochem

Abstract: The dependence of electron flux through quinone-reducing and quinol-oxidizing pathways on the redox state of the ubiquinone (Q) pool was investigated in plant mitochondria isolated from potato (Solanum tuberosum cv. Bintje, fresh tissue and callus), sweet potato (Ipomoea batatas) and Arum italicum. We have determined the redox state of the Q pool with two different methods, the Q-electrode and Q-extraction techniques. Although results from the two techniques agree well, in all tissues tested (with the exception of fresh potato) an inactive pool of QH2 was detected by the extraction technique that was not observed with the electrode. In potato callus mitochondria, an inactive Q pool was also found. An advantage of the extraction method is that it permits determination of the Q redox state in the presence of substances that interfere with the Q-electrode, such as benzohydroxamate and NADH. We have studied the relation between rate and Q redox state for both quinol-oxidizing and quinone-reducing pathways under a variety of metabolic conditions including state 3, state 4, in the presence of myxothiazol, and benzohydroxamate. Under state 4 conditions or in the presence of myxothiazol, a non-linear dependence of the rate of respiration on the Q-redox state was observed in potato callus mitochondria and in sweet potato mitochondria. The addition of benzohydroxamate, under state 4 conditions, removed this non-linearity confirming that it is due to activity of the cyanide-resistant pathway. The relation between rate and Q redox state for the external NADH dehydrogenase in potato callus mitochondria was found to differ from that of succinate dehydrogenase. It is suggested that the oxidation of cytoplasmic NADH in vivo uses the cyanide-resistant pathway more than the pathway involving the oxidation of succinate. A model is used to predict the kinetic behaviour of the respiratory network. It is shown that titrations with inhibitors of the alternative oxidase cannot be used to demonstrate a pure overflow function of the alternative oxidase.

Bioblast editor: Gnaiger E

Selected quotes

  • .. interactions between oxidizing and reducing pathways are crucial for understanding the kinetics of mitochondria1 respiration. The aim of this study is therefore to investigate the kinetics of quinone-reducing and quinol-oxidizing pathways and determine the relationship between these kinetic properties and the activity of the alternative oxidase. This was studied in tissues (a) without alternative pathway activity, i.e. fresh potatoes, (b) with inducible activity of this pathway, i.e. potato callus, and (c) with constitutive activity of the alternative pathway, i.e. sweet potatoes, and with high activity of this pathway, Arum italicurn.
  • Q-2 was assumed to be fully oxidized on addition of Q-2 to mitochondria (in the absence of substrate) and fully reduced upon anaerobiosis or upon complete inhibition of quinol-oxidizing pathways. Mitochondria (0.28 mg protein) in standard reaction medium (see above) were incubated with 1.4-3.6 µM Q-2. .. The concentrations of added Q-2 used in these experiments had no detectable effect on the rate of 02 uptake.
  • The dependence of the rate of electron transfer through the oxidizing enzymes on the redox state of the Q-pool was studied by malonate titrations. .. In fresh potato mitochondria (S. tuberosum), the cyanide-resistant pathway is not present and Fig. 1A shows that under state 3 and state 4 conditions the respiration rate is proportional to the redox state of the Q-pool. - redox state expressed as QH2 fraction
  • Comment: Succinate as substrate without rotenone may activate not only the succinate pathway into the Q-junction, but through mtMDH support the rotenone-sensitive NADH-linked pathway, and as such represents a dual NS-pathway state, with possibly varying contributions of the N- and S-pathway in the LEAK and OXPHOS states (state 4 and state 3), and at different inhibitory malonate concentrations.
  • The dependence of the rate of electron transfer through the reducing enzymes on the redox state of the Q-pool was studied by myxothiazol titrations. .. during myxothiazol titrations the Q-pool becomes further reduced .. for potato callus mitochondria oxidizing succinate under state 3 and state 4 conditions.
  • Complications sometimes arise when the redox poise of the Q-pool is measured with the Q-electrode during oxidation of external NADH [18] or benzohydroxamate because of electrode interference.
  • The Q-pool of mitochondria from fresh potatoes was completely oxidized prior to the addition of a substrate, but when callus growth was induced, the Q-pool became approximately 50 % reduced even before addition of a substrate. Similarly, inactive Q-pools were observed in sweet potato and A. italicurn. In A. italicurn oxidized short-chain ubiquinone homologues seem to form an inactive pool which constitutes at least 15 % of the total Q-pool and is present in addition to the 25 % of the inactive Q-10 pool (Table 1). - based on the Q-extraction technique
  • 25-50 % metabolically inactive quinol has been found in pigeon heart mitochondria, which do not possess cyanide-resistant respiration [19].
  • In potato callus mitochondria it can be concluded that two metabolically inactive pools are present, namely an inactive ubiquinone and an inactive ubiquinol pool. .. Inactive pools of Q and QH2 are only detected by the extraction procedure. Extrapolation of the data suggests that inactive pools constitute 47 % (QH2) and 10 % (Q) of the total pool size.
  • The presence of Q-1 or Q-2 has no significant effect on the redox state of Q-10 (Table 2).
  • When inactive pools are taken into account in determination of the redox state from the electrode, both techniques give a similar relationship between respiratory rate and redox state in potato callus mitochondria under state 4 conditions (Fig. 3B).
  • The uninhibited state 3 respiration activity with NADH is higher than with succinate and the Q-pool is rather more reduced with NADH than with succinate.
  • Comment: From Figure 5 it appears that OXPHOS capacity with succinate is higher than with NADH. Is this a misunderstanding?

Cited by

  • Komlodi et al (2021) Simultaneous measurement of respiration and redox state of the Coenzyme Q pool in mitochondrial preparations. Bioenerg Commun 2021.3 doi:10.26124/bec:2021-0003
  • Komlodi et al (2021) Hydrogen peroxide production, mitochondrial membrane potential and the redox state of the coenzyme Q measured at tissue normoxia and experimental hyperoxia in heart mitochondria. MitoFit Preprints 2021 (in prep)


Regulation: Q-junction effect 

MitoFit 2021 CoQ, MitoFit 2021 Tissue normoxia