oxidative phosphorylation


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oxidative phosphorylation:

see phosphorylationphosphorylation,
chemical process in which a phosphate group is added to an organic molecule. In living cells phosphorylation is associated with respiration, which takes place in the cell's mitochondria, and photosynthesis, which takes place in the chloroplasts.
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Oxidative Phosphorylation

 

the synthesis in living cells of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and phosphoric acid at the expense of energy that derives from the oxidation of an organic substrate. As a result of oxidative phosphorylation, cells accumulate and subsequently utilize ATP—the most important high-energy compound known —to provide the energy for life processes. The principal substrates that are involved in oxidative phosphorylation are the organic acids that are formed in the tricarboxylic acid cycle.

Oxidative phosphorylation was first discovered in 1930 by the Soviet biochemist V. A. Engel’gardt. In 1939, V. A. Belitser and E. T. Tsybakova demonstrated that oxidative phosphorylation is associated with the transfer of electrons along the respiratory enzyme chain, which is located—as was later determined—in the inner mitochondrial membrane. Electrons enter the respiratory chain from reduced nicotinamide-adenine dinucleotide (NAD) or nicotinamide-adenine dinucleotide phosphate (NADP) and are successively transferred by coenzyme Q from compounds with a more negative oxidation-reduction potential to ones with a more positive potential.

The transfer of electrons along the chain terminates with the reduction of O2 by the complex enzyme cytochrome oxidase. Thus, substrate oxidation by oxygen is dependent on a series of oxidation-reduction reactions. After each reaction, the energy that accumulates in each molecule of oxidized substrate is released in small amounts, which ensures the maximum possible utilization of the energy; this maximum utilization occurs at energy conjugation points. The enzyme complex ATP-synthetase synthesizes ATP from ADP and phosphoric acid; it also controls the reverse process, the breakdown of ATP.

The ratio of P to O reflects the quantity of phosphate that is bonded during ADP phosphorylation relative to the amount of O2 that is absorbed. The transfer of two electrons through an energy conjugation point yields one molecule of ATP. The ratio of P to O is 3 for NAD oxidation and 2 for the oxidation of succinic acid.

S. A. OSTROUMOV

oxidative phosphorylation

[‚äk·sə‚dād·iv ‚fäs·fə·rə′lā·shən]
(biochemistry)
Conversion of inorganic phosphate to the energy-rich phosphate of adenosinetriphosphatase by reactions associated with the electron transfer system.
References in periodicals archive ?
Treatment of the mitochondria with the herbicide formulation resulted in uncoupling of oxidative phosphorylation, an effect not seen when the mitochondria were treated with glyphosate alone.
Primary mitochondrial defects arise as a direct consequence of gene mutations that impair aerobic ATP synthesis, while secondary mitochondrial dysfunction is characterized by deficits in oxidative phosphorylation that result indirectly from other genetic or metabolic derangements [7, 9].
New lines of evidence show that mitochondrial oxidative phosphorylation is required for efficient execution of apoptosis, and mitochondria devoid of mtDNA, unable to conduct oxidative phosphorylation, have a resistant apoptotic phenotype.
The flux between glycolysis and oxidative phosphorylation not only is a marker of differentiation status but is also essential for stem cell fate.
Type I muscle fibers, also known as oxidative fibers, are rich in mitochondria and mainly produce energy through oxidative phosphorylation. Type II muscle fibers have a lower mitochondrial content and mainly produce ATP through the glycolytic pathway; these fibers can be further classified as type IIa, IIb, and IIx.
ALTERATIONS IN THE OXIDATIVE PHOSPHORYLATION COMPLEXES
The reaction is due to deficient coupling of oxidative phosphorylation. [19] The heterogeneity in mitochondrial morphology observed in oncocytes is suggestive of an alteration of these organelles.
Xu indicates that p53 indeed halts the initiation of tumors by reducing the oxidative phosphorylation that produces genome toxins.
(31) Many chemicals can slow or block mitochondrial function via direct or indirect inhibition of oxidative phosphorylation. These include barbituric acid, many phenols, ethanol, and a number of pesticides to name a few.
The ISO 10993-11 standard's Annex G lists the following non-endotoxin pyrogenic substances: cytokines, prostaglandins, inducers, neurotransmitters, uncoupling agents of oxidative phosphorylation, N-phenyl-P-naphthylamine, Aldo-[alpha]-naphthylamine, and metals such as nickel salts.
Mitochondria are the main sites of ROS production and the main targets of ROS after cerebral ischemia leading to injuries of phospholipid membrane and abnormality in oxidative phosphorylation process of ATP (3).
A systemic shift was observed in glucose metabolism from oxidative phosphorylation to aerobic glycolysis.