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Regulation of Oxidative Phosphorylation:- Oxidative Phosphorylation Is Regulated by Cellular Energy Needs

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  716

2026-06-23

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Regulation of Oxidative Phosphorylation:- Oxidative Phosphorylation Is Regulated by Cellular Energy Needs

The rate of respiration (O₂ consumption) in mitochondria is tightly regulated; it is generally limited by the availability of ADP as a substrate for phosphorylation. Dependence of the rate of O₂ consumption on the avail ability of the Pi acceptor ADP, the acceptor control of respiration, can be remarkable. In some animal tissues, the acceptor control ratio, the ratio of the maximal rate of ADP-induced O₂ consumption to the basal rate in the absence of ADP, is at least ten.

The intracellular concentration of ADP is one measure of the energy status of cells. Another, related measure is the mass-action ratio of the ATP-ADP system, [ATP]/([ADP][Pi]). Normally this ratio is very high, so the ATP-ADP system is almost fully phosphorylated. When the rate of some energy-requiring process (protein synthesis, for example) increases, the rate of breakdown of ATP to ADP and Pi increases, lowering the mass-action ratio. With more ADP available for oxidative phosphorylation, the rate of respiration increases, causing regeneration of ATP. This continues until the mass-action ratio returns to its normal high level, at which point respiration slows again. The rate of oxidation of cellular fuels is regulated with such sensitivity and precision that the [ATP]/([ADP][Pi]) ratio fluctuates only slightly in most tissues, even during extreme variations in energy demand. In short, ATP is formed only as fast as it is used in energy-requiring cellular activities.