Cholesterol Oxidase (Cox)Cholesterol oxidase belongs to the family of oxidoreductases and is a monomeric double functional FAD-containing enzyme (flavoenzyme). It is simple, specific, and highly sensitive enzyme.  It catalyzes the chemical reaction

cholesterol + O2  ----> cholest-4-en-3-one + H2O2

Various names of the enzyme include  cholesterol: oxygen oxidoreductase., 3beta-hydroxysteroid:oxygen oxidoreductase and cholesterol- O2 oxidoreductase, 3beta-hydroxy steroid oxidoreductase. It specifically acts on the CH-OH group of donor. COX was first isolated and defined from Rhodococcus erythropolis. Later, it was discovered that COX is  produced as intracellular or extracellular enzyme by many Gram-positive and Gram-negative bacteria such as Actinomyces lavendulae , Arthrobacter rhodochrous, Arthrobacter simplex, Pseudomonas spp., Rhodococcus equi , Streptomyces spp., Nocardia rhodochrous, Nocardia erythropolis, Mycobacterium spp. , Corynebacterium cholesterolicum, Bacillus spp. , Streptomyces griseocarneus, Streptomyces violascens, Schizophyllum commune, Gamma Proteobacterium, Brevibacterium sterolicum. Actinomyces is the most prominent COX group. 

Today COX is widely used as enzymes for chemical reactions in laboratories for bile acid synthesis, among others. It is also widely used for determination of serum cholesterol in blood ( serum cholesterol assay)- monitoring of high-density lipoprotein (HDL) cholesterol and low-density lipoprotein (LDL) cholesterol  , which is related to coronary heart disease, atherosclerosis, lipid disorders, thrombosis etc. The chemical is a potential parricide because it has insecticidal activity and is used for pest control in transgenic crops. For example insecticidal activity against cotton boll weevil (Anthonomus grandis). The enzyme is also used for steroids analysis in food samples, stearic configuration determination of 3β-hydroxysteroids and 3-ketosteroids.

Bacteria specific activities of COX

  • Streptomyces sp.- insecticidal protein production
  • Rhodococcus equi- damage of membranes, opportunistic infection in severally immune-suppressed conditions e.g. HIV infection
  • Nocardia- measurement of serum cholesterol.
  • Burkholeria and Chromobacterium sp.- tolerance of detergents, organic and thermal solvents

Rhodochorus erythropolis- Biocatalysis , oxidations of cyclic allylic, bicyclic and trycyclic alcohol for synthesis of ergot alkaloids