THE ROLE OF OXYGEN IN THE REDUCTION OF TETRAZOLIUM SALTS WITH NADH MEDIATED BY 5-METHYL PHENAZONIUM METHYL SULFATE - AN EPR AND VOLTAMMETRIC STUDY

The reduction of tetrazolium salts (namely INT, MTT and BNT) with NADH in the presence of catalytic amounts of PMS (5-methylphenazonium meth ylsulfate) was studied, and the influence of oxygen on the system was considered. The redox potentials of all the investigated compounds, th e kinetic measurements, as well as the application of the Marcus theor y confirmed that PMS and tetrazolium ions are reduced by NADH through an inner-sphere mechanism. The EPR investigations led to the detection of all possible radical species coming from PMS and tetrazolium ions and are in agreement with a mechanism which excludes any role of oxyge n in the system NADH/PMS/tetrazolium for the formation of formazan.