The modified Q-cycle: A look back at its development and forward to a functional model

• Published in: Biochimica et biophysica acta. Bioenergetics 2021-08, Vol.1862 (8), p.148417-148417, Article 148417
• Main Author: Crofts, Antony R.
• Format: Article
• Language: English
• Subjects: bc1 complex; Glutamate-295; Intermediate state in Qo-site reaction; Proton-coupled electron transfer; Q-cycle
• ISSN: 0005-2728; 1879-2650
• DOI: 10.1016/j.bbabio.2021.148417

On looking back at a lifetime of research, it is interesting to see, in the light of current progress, how things came to be, and to speculate on how things might be. I am delighted in the context of the Mitchell prize to have that excuse to present this necessarily personal view of developments in areas of my interests. I have focused on the Q-cycle and a few examples showing wider ramifications, since that had been the main interest of the lab in the 20 years since structures became available, - a watershed event in determining our molecular perspective. I have reviewed the evidence for our model for the mechanism of the first electron transfer of the bifurcated reaction at the Qo-site, which I think is compelling. In reviewing progress in understanding the second electron transfer, I have revisited some controversies to justify important conclusions which appear, from the literature, not to have been taken seriously. I hope this does not come over as nitpicking. The conclusions are important to the final section in which I develop an internally consistent mechanism for turnovers of the complex leading to a state similar to that observed in recent rapid-mix/freeze-quench experiments, reported three years ago. The final model is necessarily speculative but is open to test.