Electron transport regulation

Campbell D, Houmard J, and Tandeau de Marsac N. Electron transport regulates cellular differentiation in the filamentous cyanobacterium Calothrix. Plant Cell 1993 5 451-463. 

Proton transport via complexes I, III, and IV takes place vectorially from the matrix into the intermembrane space. When electrons are being transported through the respiratory chain, the concentration in this space increases—i. e., the pH value there is reduced by about one pH unit. For each H2O molecule formed, around 10 H ions are pumped into the intermembrane space. If the inner membrane is intact, then generally only ATP synthase (see p. 142) can allow protons to flow back into the matrix. This is the basis for the coupling of electron transport to ATP synthesis, which is important for regulation purposes (see p. 144). 

First isolated from human urine, biopterin (Fig. 15-17) is present in liver and other tissues where it functions in a reduced form as a hydroxylation coenzyme (see Chapter 18).338 It is also present in nitric oxide synthase (Chapter 18).341/342 Other functions in oxidative reactions, in regulation of electron transport, and in photosynthesis have been proposed.343 Neopterin, found in honeybee larvae, resembles biopterin but has a D-erythro configuration in the side chain. The red eye pigments of Drosophila, called drosopterins, are complex dimeric pterins containing fused 7-membered rings (Fig. 15-17).344 345... 

The observed dependence of the rate of electron tunneling on the orientation of the reacting particles suggests that orientation of porphyrin rings can perhaps serve as an instrument regulating the rate of electron transport during photosynthesis. 

The TCA cycle is carefully regulated to ensure that its level of activity relates to cellular needs. The cycle serves two functions (1) furnishing reducing equivalents (as NADH and to a lesser extent as FADH2) to the electron-transport chain, and (2) by means of side reactions, providing substrates for biosynthesis reactions. Both of these functions are reflected in the regulation of the cycle. 

Mattoo, A.K., U. Pick, H. Hoffmann-Falk, and M. Edelman (1981). The rapidly metabolized 32000-dalton polypeptide of the chloro-plast is the proteinaceous shield regulating photosystem II electron transport and mediating diuron herbicide sensitivity. Proc. Natl. Acad. Scl, 78 1572-1576. 

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