An oxygen electrode-based assay of catalase activity as a rapid method for estimating the bacterial content of foods

An oxygen electrode-based assay of catalase was developed as a simple method of assessing contamination by bacteria capable of respiration. The method gave a rapid and reasonable quantification of cell numbers in pure cultures and was able to detect 10³ bacteria/ml in some cases. The sensitivity of the method was dependent on the identity of the culture and when applied to foods the sensitivity was reduced due to the presence of non-microbial catalase. The use of electropositively charged filters to remove the organisms from the food sample improved the sensitivity and the relationship between catalase activity and cell numbers in some foods.     

Intravascular oxygen monitoring with a polarographic oxygen cathode

Thin flexible oxygen cathodes coated with heparin-dispersed cellulose diacetate were prepared for an intravascular monitoring of blood PO₂ The effect of the thickness of cellulose diacetate on various characteristics of the cathode, such as its sensitivity, response, residual current, moving artefact, linearity, and protection against poisoning, were measured. Coating with six to ten layers of 7.5% cellulose diacetate resulted in a high level of protection for cathode against poisoning by blood constituents, while still leaving a sufficiently rapid response. An instillation system using heparinized saline has been designed for further prevention of local blood coagulation. At the same time this system maintains a stable conductance of the salt bridge and furthmore, enables invivo calibration of the cathode sensitivity by supplying an instillation solution of a known oxygen tension. Using this electrode system, various intravascular PO₂ measurements have been carried out, and one representative result is shown. The advantages and disadvantages of this type of separated electrode system compared with the combined type electrode are also discussed in detail.     

A more sensitive modification of the catalase assay with the Clark oxygen electrode : Application to the kinetic study of the pea leaf enzyme

A modification of the method of catalase determination by means of the Clark oxygen electrode is described. The assay is based on measurement of the initial rate at which oxygen is released by catalase in an oxygen-free buffer. Displacement of oxygen was brought about by flushing with nitrogen, and the substrate used was hydrogen peroxide at a 33.5 m final concentration. The method is rapid and can be used with crude catalase preparations. Its sensitivity is at least 20 times higher than that of previous methods; it has an interval of measurable activity of about 0.01–8.4 μmol of O₂/min and, therefore, is applicable to an 840-fold range of catalase concentrations. This modification was applied to the kinetic study of crude extracts of pea leaf catalase. An apparent K_m of 0.190 was calculated.     

Improved assay for catalase based upon steady-state substrate concentration

A modification of the polarographic assay for catalase is described that is based upon automatic titration of a buffered H₂O₂-catalase reaction mixture with a more concentrated H₂O₂ solution such that there is no significant change in the volume of the reaction mixture. The recorded rate of addition of the titrant required to maintain a steady-state substrate concentration yields enzyme activity measurements in terms of actual reaction rate instead of the less satisfactory rate constant for H₂O₂ decomposition, as is the case for most extant assays for catalase. An additional advantage of the new method is that the reaction can be easily carried out at considerably lower temperature and substrate concentrations than can be employed practicably in other types of assays for this enzyme. Both of these features are desirable to minimize the formation of inactive catalase-H₂O₂ complexes. The improved assay works satisfactorily for measuring catalase activity in rat tissue homogenates.