Glucose release measurements from liposomes with an oxygen electrode

A method for measuring glucose release from liposomes by means of an oxygen electrode is described. The glucose concentration is determined from the initial rates of oxygen reduction catalysed by glucose oxidase. The reduction is directly proportional to either glucose (0.066-3.0 mM) or enzyme concentration (0.3-10 μg). The enzyme does not penetrate lipid bilayers and free glucose can be measured directly. Trapped glucose can be released and measured in the presence of detergents which do not interfere with the assay. By using appropriate calibration curves, glucose concentrations could be determined under extreme conditions of pH (3-9.5), temperature (10-51 °C), and in the presence of various salts and buffers. The application of polarographic methods for studies of the permeability of amino acids and other sugars is discussed.