GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

11. FUNDAMENTAL MECHANISMS OF METABOLISM AND ENERGY TRANSFORMATION IN MICROORGANISMS

11.6. RESPIRATORY CHAIN AND PHOSPHORYLATION (ATP SYNTHESIS) DURING ELECTRON TRANSFER

11.6.3. Arrangement and Functions of Redox Systems in the Respiratory Chain

Based on their redox potentials, the Components of the Respiratory Chain can be arranged in a sequence starting with NAD (most negative potential) and ending with cytochrome oxidase and oxygen (most positive potential) (Table 11.3 and Fig. 11.10). Quinones and Cytochromes serve as intermediate elements. These components are reduced by hydrogen provided by various Donors.

Let us examine Fig. 11.10 in more detail. Hydrogen derived via NAD by means of NADH dehydrogenase is transferred to quinone (coenzyme Q). Similarly, hydrogen from succinate is supplied to quinone (via succinate dehydrogenase), along with hydrogen obtained from the dehydrogenation of Fatty acids (via other specific dehydrogenases). Quinone acts as a specific reservoir for substrate-derived hydrogen within the respiratory chain. Some of the Enzymes involved in hydrogen transport contain FMN or FAD, as well as iron-sulfur Proteins. Reduced quinones are reoxidized by the cytochrome system. Cytochromes accept electrons and transfer them to oxygen; hydrogen is ionized and leaves the membrane (is transported outside).

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Fig. 11.10. Components of the respiratory chain in Cell/35.html">Mitochondria and Escherichia coli