Standardized device for the assay of oxygen consumption adaptable to commercial photometers

Improvements of the spectrophotometric method for the assay of oxygen consumption based on the utilization of oxyhemoglobin as oxygen donor and indicator are described with the aim to simplify and standardize the method for commercial instruments. In order to ensure a continuous stirring of the reaction medium and to maintain the optical homogeneity during the measurements, a special glass cuvette and mixing attachment adaptable to Eppendorf spectralline photometers was built. The cuvette is square shaped in cross section but it has a cylindrical hole at the base which houses the magnetic stirrer. The efficiency of the stirring depends on the ratio between the internal dimensions of the cuvette. If respiratory systems with high affinity for oxygen are to be investigated, oxyhemoglobin could be successfully replaced by its carboxypeptidase-treated derivative. Under the conditions described in this work the spectrophotometric method may be used with a wide range of preparations including soluble enzymes, isolated organelles, or particles in suspension with a pronounced tendency to sediment like isolated cells or immobilized enzymes.