Electron transport chain definition

In an experiment, a suspension of mitochondria provided with adequate oxygen and pyruvate, but no ADP, consumed oxygen at a very low rate. The relative states of reduction of components of the electron-transport chain were determined NAD, 100 percent coenzyme Q, 40 percent cytochrome b, 38 percent cytochrome c, 14 percent and cytochrome a, 0 percent. How could these data allow definition of the sites of oxidative phosphorylation ... 

The mechanism of action of the phenothiazines is still not definitely known. They tend to block important effector substances such as acetylcholine, epinephrine, and histamine. The phenothiazines produce uncoupling of phosphorylation from oxidation. They appear to act at all steps along the electron transport chain. Cytochrome oxidase, succinoxidase, and adenosine triphosphatase are inhibited. Some data indicate that the phenothiazines may decrease the permeability of storage granules for brain amines. 

The electron transport chain that links the two photosystems consists of pheo-phytin, plastoquinone, a complex of plant cytochromes (the b —f complex), a copper-containing protein called plastocyanin (PC), and the oxidized form of Pyoo (see Figure 22.6). The complex of plant cytochromes consists of two i-type cytochromes (cytochrome and a c-type cytochrome (cytochrome/). This complex is similar in structure to the bc complex in mitochondria and occupies a similar central position in an electron transport chain. This part of the photosynthetic apparatus is the subject of active research. There is a possibility that a cycle (recall this from Section 20.2) may operate here as well, and the object of some of this research is to establish definitely whether this is so. In plastocyanin, the copper ion is the actual electron carrier the copper ion exists as Cu(ll) and Gu(l) in the oxidized and reduced forms, respectively. This electron transport chain has another similarity to that in mitochondria, that of coupling to ATP generation. 

Some of these steps can be bypassed in nonphos-phorylating particles, and the spectrophotometric methods do not exclude the possibility that some of the components that seem to participate in the electron transport chain are only parasites. Definite information on these mechanisms will be obtained only when in vitro reconstruction with purified enzyme systems is possible. 

When investigating the electron transport processes in mitochondria and chloroplasts and bacteria, it is simplest to assume that the interaction of the chain components follows the mass action law.11-14 That would mean that the free movement of individual elements of the chain in the membrane is possible and also transfer of the charge by accidental collisions. However, transfer of electrons during both respiration and photosynthesis passes along the electron transfer chain organized into definite structural complexes. Consequently a molecule possessing an electron can donate it to a... 

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