الفهرس 
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Abstract
Cholesterol oxidase was isolated from Staphylococcus epidermidis.
Maximum production of cholesterol oxidase was achieved with 8% (v/v) inoculum for 48 h.
Glycerol and galactose were the best carbon sources for enzyme production whereas glucose and lactose were the best source for the growth.
Soybean meal and yeast were the best nitrogen source for cholesterol oxidase production.
The pH 7.5 and temperature 40°C supported the maximum production of cholesterol oxidase and the growth.
Benzyladenine and coumarin were inducer for cholesterol oxidase activity.
The enzyme was purified using 60% ammonium sulphate, DEAE-cellulose and Sephadex G-200 with specific activity 62 U mg-1 protein and 43.5– fold.
The optimal concentration of cholesterol was 8 mM with Km value of 0.26 mM and Vmax of 23.8 U mg-1 protein.
The optimal pH value for cholesterol oxidase was 8.0 and the optimal temperature was 40°C.
Ca2+, Mg2+ and Mn2+ were activators whereas Al3+, Cu2+, Zn2+ and Ba2+ were inhibitors. K+ did not affect the enzyme activity.
GSH, DTT, 2-ME and cysteine activated cholesterol oxidase activity. GSH was the best activator.
Spermine, spermidine and putrescine activated cholesterol oxidase activity.
The Vmax/Km value increased in presence of cysteine, L-methionine, GSH and N-acetyl cystiene.
SDS inactivated cholesterol oxidase activity and the inactivation was dependent on its concentration.
The enzyme was stable in presence of benzene and cyclohexane.
Tween 80, Tween 60 and PB were activators whereas SDS and lecithin were inhibitors.
Alginate, glutaraldehyde and betaine were the best stabilizers for cholesterol oxidase activity.
Glycerol, sorbitol, mannitol and xylitol offered good stability for the enzyme activity at 60˚C.
Collagen, malto dextran, BSA and proline offered variable stability for the enzyme at 60°C.
PEG at 45%, 65% and 85% protected the enzyme from heat inactivation at 60°C.
Modification of cholesterol oxidase with various anhydrides: CA, PA, SA and MA retained appreciable enzyme activity.
Cholesterol oxidase activity was inhibited by PGO, NAI, NEM and DEPC at various concentrations indicating the essentiality of arginine, tyrosine, sulfhydryl and histidyl groups for cholesterol oxidase catalysis.
GC was good stabilizer for the cholesterol oxidase enzyme at 60°C.
Free and immobilized cholesterol oxidase expressed appreciable resistant to both pepsin and trypsin.
NaCl at 6% (w/v) expressed the best solubilizate rate of fresh, frozen and dried egg yolk.
Solubilization with NaCl was better than saponification of egg yolk for determining the cholesterol content.