Moore 1991 Plant Physiol

Moore AL, Dry IB, Wiskich JT (1991) Regulation of electron transport in plant mitochondria under state 4 conditions. Plant Physiol 95:34-40.

» PMID: 16667977 Open Access

Moore AL, Dry IB, Wiskich JT (1991) Plant Physiol

Abstract: The regulation of electron transport in pea (Pisum sativum L.) leaf mitochondria under state 4 conditions has been investigated by simultaneously monitoring oxygen uptake, the steady-state reduction level of ubiquinone, and membrane potential. Membrane potentials were measured using a methyltriphenylphosphonium electrode while a voltametric technique was used to monitor changes in the steady-state reduction levels of quinone. It was found that the addition of glycine to mitochondria oxidising malate in state 4 led to a marked increase in the rate of O₂ uptake and increased both the membrane potential and reduction level of the quinone pool. Increases in the state 4 respiratory rate were attributed to both an increase in driving flux, due to increased Q-pool reduction, and in membrane potential. Due to the nonohmic behavior of the inner membrane, under these conditions, an increase in potential would result in a considerable rise in proton conductance. Measurement of dual substrate oxidation, in the presence of n-propylgallate, revealed that the increase in respiratory activity was not mediated by the alternative oxidase. Similar increases in membrane potential and the level of Q-pool reduction were observed even in the presence of rotenone suggesting that the rotenone-insensitive pathway is a constitutive feature of plant mitochondria and may play a role in facilitating rapid state 4 rates even in the presence of a high energy charge.

• Bioblast editor: Gnaiger E

• Energy charge - a different definition.

Selected quotes and comments

• "The transition to state 4 conditions increases the protonmotive force which exerts a back pressure on the respiratory chain restricting the rate of electron flow and hence overall oxygen uptake."

• Comment: Protonmotive force exerts a 'back force', whereas protonmotive pressure (Gnaiger 2020 BEC MitoPathways) creates a 'back pressure'.

• "The control of respiration in plant mitochondria is somewhat more complicated than in mammalian tissues since the majority of plant mitochondria possess, albeit to varying extents, a cyanide-insensitive alternative oxidase, and a rotenone-insensitive bypass of Complex I (10). Since electron flux via these pathways is not linked to proton extrusion (21) their engagement could make a considerable contribution to the overall respiratory rate under state 4 conditions. The degree to which the antimycin-insensitive alternative oxidase contributes to ADP-limited respiration has been generally assessed from the effect of inhibitors of this pathway on respiratory control indices (16). Inhibition of the pathway results in a marked increase in control suggesting it is engaged under state 4 conditions. More recently it has been demonstrated that the degree to which this pathway is engaged is dependent, in a nonlinear fashion, upon the level of reduction of the quinone pool (12)."

• "The redox state of Q-2 was measured voltametrically using a glassy carbon working electrode and a platinum electrode connected to Ag/AgCl reference electrode. The working electrode was poised at 360 mV with respect to the reference as previously described (22)."

• Comment: Current is converted into a voltage. In this sense, the amperometric principle of the measurement of the redox state of Q-2 using the electrochemical sensor may be considered as a "voltametric" approach, although we do not encourage to use the term "potentiometric" in this context. - Compare: O2k signals and output

Cited by

• Komlódi T, Cardoso LHD, Doerrier C, Moore AL, Rich PR, Gnaiger E (2021) Coupling and pathway control of coenzyme Q redox state and respiration in isolated mitochondria. Bioenerg Commun 2021.3. https://doi.org/10.26124/bec:2021-0003

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