The Mechanism of Oxidative Phosphorylation

THE CHEMIOSMOTIC THEORY EXPLAINS THE MECHANISM OF OXIDATIVE PHOSPHORYLATION... 

The Mechanism of Oxidative Phosphorylation 1066 Box 18-D Vitamin C Ascorbic Acid... 

In an effort to elucidate the mechanism of oxidative phosphorylation, 6-hydroxy-2,2,5-trimethyl-2H-naphtho[l,2-6]pyran (183) was treated with silver(II) oxide. The product (184) was a stable quinone hemiketal (71JOC4045). 

Mitchell postulated the chemiosmotic hypothesis for the mechanism of oxidative phosphorylation. 

Losada, M. 1978. Energy-transducing redox systems and the mechanism of oxidative phosphorylation. Bioelectrochem. Bioenerg., 5, 296-310. 

ATP formation coupled to electron flow in mitochondria is usually called oxidative phosphorylation. Because electron flow involves both reduction and oxidation, more appropriate names are respiratory phosphorylation and respiratory-chain phosphorylation, terminology that is also more consistent with photophosphorylation for ATP formation in photosynthesis. As with photophosphorylation, the mechanism of oxidative phosphorylation is not yet fully understood in molecular terms. Processes like phosphorylation accompanying electron flow are intimately connected with membrane structure, so they are much more difficult to study than are the biochemical reactions taking place in solution. A chemiosmotic coupling mechanism between electron flow and ATP formation in mitochondria is generally accepted, and we will discuss some of its characteristics next. 

Oxidative phosphorylation is conceptually simple and mechanistically complex. Indeed, the unraveling of the mechanism of oxidative phosphorylation has been one of the most challenging problems of biochemistry. The flow of electrons from NADH or FADH2 to O2 through protein complexes located in the mitochondrial inner membrane leads to the pumping of... 

Before we try to understand the mechanism of oxidative phosphorylation, let s first look at the molecules that carry out this complex process. Embedded within the mitochondrial inner membrane are electron transport systems. These are made up of a series of electron carriers, including coenzymes and cytochromes. All these molecules are located within the membrane in an arrangement that allows them to pass electrons from one to the next. This array of electron carriers is called the respiratory electron transport system (Figure 22.7). As you would expect in such sequential oxidation-reduction reactions, the electrons lose some energy with each transfer. Some of this energy is used to make ATP. 

Matsuno-Yagi, A., and Hatefi, Y. (1993). Studies on the mechanism of oxidative phosphorylation. ATP synthesis by submitochondrial particles inhibited at Fo by venturicidin and organotin compounds. J. Biol. Chem. 268, 6168-6173. 

We were interested in the mechanisms of oxidative phosphorylation and I thought it would be of interest to study the process in the extracts of Azotobacter vinelandii, a bacterium in which oxidative processes are very intense. The experimental plan was very simple. Bacterial extracts were incubated with ATP and inorganic P tagged with P to measure the incorporation of P into ATP. Very soon we obtained positive results stewing extensive incorporation of radioactivity. 

This brings me to the latest chapter in the field of oxidative phosphorylation and the current controversies on the mechanism of oxidative phosphorylation. Slater s formulations based on the mode of glyceraldehyde-3-phosphate dehydrogenase action became known as the chemical hypothesis. In 1961 Mitchell proposed a chemiosmotic hypothesis. ... 

In the early 1940 s, Severo was interested in oxidative phosphorylation. It must be said that although his measurements (from 1940 to approximately 1944) were most accurate and his work very brilliant, his good sense led him to abandon this area in spite of his earlier strifes and successes. At the time of this writing, approximately 30 years later, the mechanism of oxidative phosphorylation is still to be solved. 

To better comprehend the differences between the contending hypotheses of the mechanism of oxidative phosphorylation, it is useful... 

---