Lecithin/propanol-based microemulsions used as media for a cholesterol oxidase-catalyzed reaction

Cholesterol oxidase: sources, physical properties and analytical applications

Since Flegg (H.M. Flegg, An investigation of the determination of serum cholesterol by an enzymatic method, Ann. Clin. Biochem. 10 (1973) 79-84) and Richmond (W. Richmond, The development of an enzymatic technique for the assay of cholesterol in biological fluids, Scand. J. clin. Lab. Invest. 29 (1972) 25; W. Richmond, Preparation and properties of a bacterial cholesterol oxidase from Nocardia sp. and its application to enzyme assay of total cholesterol in serum, Clinical Chemistry 19 (1973) 1350-1356) first illustrated the suitability of cholesterol oxidase (COD) for the analysis of serum cholesterol, COD has risen to become the most widely used enzyme in clinical laboratories with the exception of glucose oxidase (GOD). The use is widespread because assays incorporating the enzyme are extremely simple, specific, and highly sensitive and thus offer distinct advantages over the Liebermann-Burchard analytical methodologies which employ corrosive reagents and can be prone to unreliable results due to interfering substances such as bilirubin. Individuals can now readily determine their own serum cholesterol levels with a simple disposable test kit. This review discusses COD in some detail and includes the topics: (1) The variety of bacterial sources available; (2) The various extraction/purification protocols utilised in order to obtain protein of sufficient clarification (purity) for use in food/clinical analysis; (3) Significant differences in the properties of the individual enzymes; (4) Substrate specificities of the various enzymes; (5) Examples of biological assays which have employed cholesterol oxidase as an integral part of the analysis, and the various assay protocols; (6) New steroidal products of COD. This review is not a comprehensive description of published work, but is intended to provide an account of recent and current research, and should promote further interest in the application of enzymes to analytical selectivity.

Structural and Dynamic Properties of Lecithin-Alcohol Based w/o Microemulsions: A Luminescence Quenching Study

Water-in-oil microemulsions have been made with lecithin in the presence of some alcohols. The structure of the microemulsions has been studied by steady-state and time-resolved analysis of the luminescence quenching of Ru(bipy)32+ by Fe(CN)63-. We found that well-defined microemulsions can be made only in the presence of short-chain alcohols such as propanol-1 and butanol-1. There exists a threshold for water content in order to obtain typical reverse micelles. Thus in the case of propanol-1, water/surfactant ratio wo should be above 20. By varying water content in the range 20 < wo </= 40, the microemulsion droplets suffer dramatic structural changes and the system passes through a percolation threshold. Copyright 1997 Academic Press. Copyright 1997Academic Press