The CellTiter 96® AQueous Assay is composed of solutions
of a novel tetrazolium compound (3-(4,5-dimethylthiazol-2-
yl)-5-(3-carboxy-methoxyphenyl)-2-(phenazine methosulfate;
PMS)). MTS is bioreduced by cells into a formazan product
that is soluble in a tissue culture medium. The absorbance of
the formazan at 490 nm can be measured directly from 96 well
assay plates without additional processing [23]. The conversion
of MTS into aqueous, soluble formazan is accomplished
by dehydrogenase enzymes found in metabolically active cells.
The quantity of formazan product as measured by the account
of 490 nm absorbance is directly proportional to the number of
living cells in the culture.