Purification and partial characterization of a cholesterol oxidase from Streptomyces fradiae

An extracellular cholesterol oxidase from Streptomyces fradiae (PTCC 1121) was purified in one step using DEAE-Sepharose. The purified enzyme had a molecular weight of 60 KDa. The optimum pH and temperature for activity was found to be 7 and 70 degrees C, respectively. This cholesterol oxidase was stable in pHs between 4-10 at 4 degrees C until 4 h. Thermal stability experiments showed that it has high stability and retains its full activity at 50 degrees C for 90 min. K(m) value for cholesterol oxidase was obtained to be about 7.06 x 10(-)(5) Mol.     

Cholesterol-degrading bacteria: isolation,characterization and bioconversion

Agrobacterium sp. M4, a gram negative, motile, oxidase- and catalase-positive bacterium isolated from 410 colonies from soil was found to degrade cholesterol with high efficiency (within 9 days). The first and most probably the main metabolite of cholesterol degradation was detectable on TLC from the second day of incubation, and it was identified as 4-cholestene-3-one. No substances with cyclopentenoperhydrophenanthrene structure was found under U.V. radiation at 256 and 336nm, or by staining with sulphuric acid after 9 days of incubation. Morphological, cultural and biochemical characteristics of the isolate placed it in the genus Agrobacterium although its urease activity was negative. Further investigation on this newly isolated strain is under way.     

Production of cholesterol oxidase by a newly isolated Rhodococcus sp.

Fifteen strains of microorganisms with ability to degrade cholesterol were isolated. Among them a Gram-positive, non-motile, non-sporing bacterium with meso-DAP in the cell wall and with a rod-coccus cycle showed the highest ability for cholesterol degradation. It was identified as Rhodococcus sp. strain 2C and was deposited by code 1633 in Persian type culture collection (PTCC). This strain was able to produce high levels of both extracellular and cell-bound cholesterol oxidases in media containing cholesterol as a sole carbon source. The effects of medium composition and physical parameters on cholesterol oxidase production were studied. The optimized medium was found to contain cholesterol 0.15% (w/v), yeast extract 0.3% (w/v), diammonium hydrogen phosphate 0.1% (w/v), Tween 80 (0.05%). The optimum pH and temperature for cholesterol oxidase production in optimized medium were found to be 8–30 °C respectively. Triton X-100 showed the greatest effect in releasing the cell-bound enzyme. The first and most probably the main metabolite of cholesterol degradation was purified and identified as 4-cholestene-3-one.     

The oxidation hypothesis of atherogenesis: the role of oxidized phospholipids and HDL

For more than two decades, there has been continuing evidence of lipid oxidation playing a central role in atherogenesis. The oxidation hypothesis of atherogenesis has evolved to focus on specific proinflammatory oxidized phospholipids that result from the oxidation of LDL phospholipids containing arachidonic acid and that are recognized by the innate immune system in animals and humans. These oxidized phospholipids are largely generated by potent oxidants produced by the lipoxygenase and myeloperoxidase pathways. The failure of antioxidant vitamins to influence clinical outcomes may have many explanations, including the inability of vitamin E to prevent the formation of these oxidized phospholipids and other lipid oxidation products of the myeloperoxidase pathway. Preliminary data suggest that the oxidation hypothesis of atherogenesis and the reverse cholesterol transport hypothesis of atherogenesis may have a common biological basis. The levels of specific oxidized lipids in plasma and lipoproteins, the levels of antibodies to these lipids, and the inflammatory/anti-inflammatory properties of HDL may be useful markers of susceptibility to atherogenesis. Apolipoprotein A-I (apoA-I) and apoA-I mimetic peptides may both promote a reduction in oxidized lipids and enhance reverse cholesterol transport and therefore may have therapeutic potential.