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Metabolizing Cholesterol without Oxygen

The complete aerobic mineralization of cholesterol by various bacteria has been studied in some detail. In contrast, very little is known about the metabolic mechanisms that operate under anoxic conditions. This form of cholesterol metabolism is especially mechanistically interesting because cholesterol is intrinsically difficult to attack due to its complex chemical structure, low solubility in water, low number of active functional groups, and the presence of four alicyclic rings and two quaternary carbon atoms.

Anoxic cholesterol metabolism proceeds by the oxidation of ring A followed by the hydroxylation of the terminal C-25.

In this Paper of the Week, Yin-Ru Chiang and colleagues used Sterolibacterium denitrificans to study the anoxic cholesterol metabolism and to propose the initial steps in the pathway. They showed that S. denitrificans metabolizes cholesterol anoxically via the oxidation of ring A, followed by an oxygen-independent hydroxylation of the terminal C-25 of the side chain. The anaerobic hydroxylation of a tertiary carbon using water as oxygen donor is unprecedented and may be catalyzed by a novel molybdenum containing enzyme.

FOOTNOTES

See referenced article, J. Biol. Chem. 2007, 282, 13240-13249

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