International Journal of Scientific and Innovative Research 2015; 3(1) : 1-11, P-ISSN 2347-2189, E- ISSN 2347-4971 www.ijsir.co.in 1 MICROBIAL CHOLESTEROL OXIDASES AKANKSHA SRIVASTAVA 1 , RAM NIWAS 1 , VINEETA SINGH 1 , AMREEN KHAN 2 , * C.K.M. TRIPATHI 2 1 Microbiology Division, CSIR - Central Drug Research Institute, Lucknow, India 2 Department of Biotechnology, Shri Ramswaroop Memorial University, Lucknow, India * Address for correspondence: Dr. C.K.M. Tripathi, Department of Biotechnology, Shri Ramswaroop Memorial University, Lucknow - Deva Road, Lucknow-225003, India, Email ID: ckm.tripathi@gmail.com ABSTRACT Cholesterol oxidase, a bi-functional FAD-containing microbial enzyme belongs to the family oxidoreductases which catalyzes the oxidation of cholesterol into 4-cholesten-3-one. In recent time, cholesterol oxidase has received great attention due to its wider use in clinical (determination of serum cholesterol) laboratories practice and in the bio- catalysis for the production of a number of steroids. Cholesterol oxidase (COD) has been shown to possess potent insecticidal activity, besides its use to track cell cholesterol. Moreover, this enzyme is also implicated in the manifestation of some of the diseases of bacterial (tuberculosis), viral (HIV) and non-viral prion origin (Alzheimer’s). These applications and disease mechanisms have promoted the need of screening, isolation and characterization of newer microbes from diverse habitats as a source of COD to learn more about its structural and functional aspects. In this review, we discuss microbial sources of COD, its structure and important biochemical properties besides its broad range of biological functions and applications. Keywords: Cholesterol, Steroids, Bio-catalysis, Microorganisms, Biosensors INTRODUCTION The enzyme Cholesterol oxidase (COD) (cholesterol: oxygen oxidoreductase, EC 1.1.3.6) catalyzes the oxidation of cholesterol to 4- cholesten-3-one in the presence of O 2 [1] . COD has wide applications in clinical, pharmaceuticals, food and agricultural industries which has considerably increased the demand of this enzyme. Various microorganisms are reported to produce COD with specific properties. Cholesterol oxidases are used to determine cholesterol concentration in food and blood serum by coupling of the enzyme with peroxidase [2,3] in the production of precursors for chemical synthesis of steroid hormones, degradation of dietary cholesterol in foods [4] and as biological control agent [5] . COD is a monomeric bi-functional flavin adenine dinucleotide (FAD) containing enzyme which belongs to the oxidoreductases family and acts on the CH-OH group of donor with oxygen as an acceptor. COD catalyzes the oxidation of 3 β -hydroxoysteroids and the isomerization of Δ5-6-ene-3 β฀-ketosteroid (cholest-5-en-3-one) to produce 3-4-ene-3 β฀-ketosteroid (cholest- 4- en-3-one) (Figure 1) Figure 1: Breakdown of cholesterol with the help of cholesterol oxidase SOURCES OF CHOLESTEROL OXIDASE Cholesterol oxidase has been isolated and characterized from numerous microorganisms that are found in different environments (Figure 2). The first COD enzyme was isolated from Nocardia (later Rhodococcus) erythropolis and oxidant effect of cholesterol was explored [6] . Mycobacterium sp. and Streptomyces sp. are reported from soil for COD production. COD producing microorganisms have also been isolated from food stuffs like chicken fat, pork