Chemical. CAS 1719-71-7. Formula C23H17ClN4. MW 384.86. Tetrazolium violet TZV is a tetrazolium salt TTZ, is widely used for microbiological studies as a redox indicator to indicate cellular respiration. Tetrazolium salts are colourless compounds which become coloured when reduced to formazans. Traditionally used as indicators of cell metabolism in eukaryotes and prokaryotes, they function as artificial electron acceptors and thus detect dehydrogenase activities. The production of coloured formazan is irreversible and can be quantified using spectrophotometry. TZV forms a water-insoluble formazan. This salt is positively charged and considered as cell permeable. The positive charge is thought to facilitate cellular uptake due to the membrane potential. It is generally used as indicators of cell redox activity in order to test resistance to solvents, drug susceptibility or specific substrate utilization.