The Role of the Quinones Prepared After Oxidation of Some Amines by Ceruloplasmin in the Mitochondrial Electron Transport System

1970 ◽  
Vol 11 (6) ◽  
pp. 531-537 ◽  
Author(s):  
B. Bozhkov ◽  
A. Wysokińska-Borowicz ◽  
J. Krawczyński
Keyword(s):  
Electron Transport ◽  
Transport System ◽  
Electron Transport System

scholarly journals Human blood contains circulating cell-free mitochondria, but are they really functional?

2020 ◽  
Author(s):  
Antoine Stier
Keyword(s):  
Electron Transport ◽  
Transport System ◽  
Human Blood ◽  
Electron Transport System ◽  
Complex Iv ◽  
Mitochondrial Inhibitors ◽  
Functional Part ◽  
Positive Controls

AbstractDache et al. (2020, FASEB J. 15, e2002338–15) recently reported the presence of respiratory-competent cell-free mitochondria in human blood (up to 3.7 x 106 per mL of blood), providing exciting perspectives on the potential role of these extra-cellular mitochondria. While their evidence for the presence of cell-free mitochondria in human blood is compelling, their conclusion that these cell-free mitochondria are respiratory-competent or functional has to be re-evaluated. To this end, we evaluated the functionality of cell-free mitochondria in human blood using high-resolution respirometry and mitochondria extracted from platelets of the same blood samples as positive controls. While cell-free mitochondria were present in human plasma (i.e. significant complex IV activity), there was no evidence suggesting that their mitochondrial electron transport system (ETS) was functional (i.e. respiration rate not significantly different from 0; no significant responses to ADP, uncoupler or mitochondrial inhibitors oligomycin and antimycin A). Yet, in vitro complex IV activity was detectable and even slightly higher than levels found in mitochondria extracted from platelets, suggesting that cell-free mitochondria in human blood only retain a non-functional part of the electron transport system. Despite being unlikely to be fully functional in the narrow-sense (i.e. capable of oxidative phosphorylation), circulating cell-free mitochondria may have significant physiological roles that remain to be elucidated.

scholarly journals The role of Cytochrome $$\text {b}_{6}\text {f}$$ in the control of steady-state photosynthesis: a conceptual and quantitative model

2021 ◽  
Author(s):  
J. E. Johnson ◽  
J. A. Berry
Keyword(s):  
Steady State ◽  
Electron Transport ◽  
Transport System ◽  
Carbon Metabolism ◽  
Quantitative Model ◽  
Electron Transport System ◽  
Photochemical Quenching ◽  
Photosynthetic Control ◽  
Non Photochemical Quenching

AbstractHere, we present a conceptual and quantitative model to describe the role of the Cytochrome $$\hbox {b}_{6}\hbox {f}$$ b 6 f complex in controlling steady-state electron transport in $$\hbox {C}_{3}$$ C 3 leaves. The model is based on new experimental methods to diagnose the maximum activity of Cyt $$\hbox {b}_{6}\hbox {f}$$ b 6 f in vivo, and to identify conditions under which photosynthetic control of Cyt $$\hbox {b}_{6}\hbox {f}$$ b 6 f is active or relaxed. With these approaches, we demonstrate that Cyt $$\hbox {b}_{6}\hbox {f}$$ b 6 f controls the trade-off between the speed and efficiency of electron transport under limiting light, and functions as a metabolic switch that transfers control to carbon metabolism under saturating light. We also present evidence that the onset of photosynthetic control of Cyt $$\hbox {b}_{6}\hbox {f}$$ b 6 f occurs within milliseconds of exposure to saturating light, much more quickly than the induction of non-photochemical quenching. We propose that photosynthetic control is the primary means of photoprotection and functions to manage excitation pressure, whereas non-photochemical quenching functions to manage excitation balance. We use these findings to extend the Farquhar et al. (Planta 149:78–90, 1980) model of $$\hbox {C}_{3}$$ C 3 photosynthesis to include a mechanistic description of the electron transport system. This framework relates the light captured by PS I and PS II to the energy and mass fluxes linking the photoacts with Cyt $$\hbox {b}_{6}\hbox {f}$$ b 6 f , the ATP synthase, and Rubisco. It enables quantitative interpretation of pulse-amplitude modulated fluorometry and gas-exchange measurements, providing a new basis for analyzing how the electron transport system coordinates the supply of Fd, NADPH, and ATP with the dynamic demands of carbon metabolism, how efficient use of light is achieved under limiting light, and how photoprotection is achieved under saturating light. The model is designed to support forward as well as inverse applications. It can either be used in a stand-alone mode at the leaf-level or coupled to other models that resolve finer-scale or coarser-scale phenomena.

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