The decrease of cytochrome c oxidase activity by 15-deoxyspergualin results in enhancement of XTT reduction in cultured cells

Exposure to immunosuppressant, 15-deoxyspergualin (DSG) induced enhanced fo rmazan producing activity from XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl )-2H-tetrazolium-5- carboxanilide, sodium salt) in cultured cells, but not from MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). Fo rmazan generation from XTT is known to be stimulated by cytochrome c oxidas e (COX) inhibitors such as KCN and NaN3, whereas MTT reduction is not affec ted by them. So, the effect of DSG on COX was examined. DSG did not directl y inhibit the enzyme, but the cellular enzyme activity was decreased by exp osure to DSC. It was thought that stimulation of XTT reduction by DSG resul ted from the decrease of cellular cytochrome c oxidase activity.