Interaction of certain cationic dyes with the respiratory chain of rat liver mitochondria

Abstract

Cationic dyes of the cyanine type have been observed to specifically inhibit NAD-linked respiration in rat liver mitochondria, with 50% inhibition occurring at about 0.2 mumol/g of mitochondrial protein. The dyes show no effect on succinate oxidation or coupled phosphorylation in the range which completely inhibits NADH oxidation. This specific inhibition was found with all cyanine dyes tested, but, with the possible exception of pyronin B, was not observed with other cationic dyes such as safranine O, rhodamine dyes, or with simple derivatives of the quinaldinium ring structure. The inhibition was observed to be both time- and concentration-dependent, with the half-time for full inhibition determined to be on the order of 15 to 30 s at 25 degrees C. Furthermore, the inhibition was totally dependent on the energization of the mitochondrial membrane by either substrate oxidation or the presence of ATP. The explanation of the energy dependence of the inhibition by cyanine dyes as the simple requirement for energy-linked dye concentration within the mitochondria is not supported by the relatively slow onset of inhibition as compared with the very rapid rate of dye uptake observed. Furthermore, inhibition of energy-requiring, succinate-linked NAD reduction in submitochondrial particles was observed to be inhibited by dyes, while fumarate reduction by NADH was found to be inhibited significantly only in the presence of ATP in addition to the dye. The energy requirement for electron transport inhibition in submitochondrial particles indicates that energy-dependent accumulation of the dyes by mitochondria cannot alone explain the energy requirement for the cyanine dye inhibition of NADH oxidation.