GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

11. MAIN MECHANISMS OF METABOLISM AND ENERGY CONVERSION IN MICROORGANISMS

11.5. PATHWAYS OF GLUCOSE AND OTHER CARBOHYDRATE CATABOLISM

11.5.7. Pyruvate Oxidation

Glucose Catabolism yields Pyruvate, one of the most crucial metabolites that serves as a precursor for numerous products.

The overwhelming majority of microorganisms are oxidative, converting pyruvate to acetyl-coenzyme A (acetyl-CoA). The Formation of Acetyl-CoA from pyruvate can proceed via the following reactions:

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where Fd is ferredoxin;

Reaction (1) is catalyzed by a multienzyme pyruvate dehydrogenase complex consisting of three Enzymes, one of which is pyruvate dehydrogenase. This complex Functions in almost all aerobic microorganisms. Obligate anaerobes lack the pyruvate dehydrogenase complex.

Reaction (2) is catalyzed by the enzyme pyruvate:ferredoxin oxidoreductase. This enzyme is of particular importance in many anaerobic Bacteria (e.g., Clostridia).

Reaction (3) is catalyzed by the enzyme pyruvate formate-lyase. It has been detected in many anaerobic bacteria that produce formic acid (performing mixed-acid Fermentation), particularly in enterobacteria, as well as in phototrophic bacteria.

Yeasts and certain ethanol-producing bacteria possess a fourth enzyme that oxidizes pyruvate:

The enzyme pyruvate decarboxylase cleaves pyruvate into acetaldehyde and carbon dioxide. Acetaldehyde is subsequently reduced to ethanol.