Enzyme-caytalyzed oxidation of cholesterol in supercritical carbon dioxide

✍ Scribed by T. W. Randolph; H. W. Blanch; J. M. Prausnitz

• Publisher: American Institute of Chemical Engineers
• Year: 1988
• Tongue: English
• Weight: 654 KB
• Volume: 34
• Category: Article
• ISSN: 0001-1541
• DOI: 10.1002/aic.690340813

✦ Synopsis

Supercritical carbon dioxide was studied as a solvent for the enzymatic oxidation of cholesterol with molecular oxygen. Enzymes isolated from Strepfomyces sp., Norcardia sp., Pseudornonas sp., and Gloeocysficum chrysocreas are active in supercritical carbon dioxide.

For the oxidation of cholesterol to cholest-4-ene-3-one (via cholesterol oxidase from Gloeocysticum chrysocreas, turnovers are almost two orders of magnitude higher than those found in aqueous solutions; initial rates of the reaction catalyzed by Sfrepfomyces sp. in supercritical carbon dioxide are comparable to or greater than those found in aqueous solutions. Cholesterol oxidase from Gloeocysticum chrysocreas is stable in supercritical carbon dioxide at 100 bar and 35OC, while the enzyme from Sfrepfomyces sp. is not. A trace amount of water is necessary for catalysis in carbon dioxide.

The rate of oxidation is increased markedly by addition of small amounts of tert-butanol and iso-butanol, moderately by ethanol, slightly by acetone and n-butanol, and not at all by addition of methanol. Solubility data cannot explain these observations. EPR spectroscopy reveals no large conformational changes in the enzyme from Gloeocysficum chrysocreas as a function of carbon dioxide pressure or cosolvent addition. However, EPR spectroscopy indicates that aggregation of cholesterol molecules in supercritical carbon dioxide is strongly affected by changes in pressure or cosolvent content. The degree of cholesterol aggregation correlates well with observed rate enhancements.