Interaction of bromosulfophthalein with mitochondrial membranes-inhibition of respiration

Bromosulfophthalein reversibly inhibits mitochondrial respiration. Most sensitive is state 3 respiration (K_i about 3 nmole/mg protein independent of substrate). At higher concentrations (20–100 nmole/mg protein) state 4 respiration and uncoupled respiration are also inhibited. This inhibition is substrate dependent. With succinate, inhibition appears to be noncompetitive at low concentrations and competitive above 1 mM succinate (half-maximal inhibition at 9–17 nmole/mg protein, dependent on succinate concentration). Substrate permeation seems to be not the only sensitive step in oxidation, as is deduced from similar results obtained on glycerol phosphate respiration. By use of artificial electron shunts and by difference spectroscopy, individual dehydrogenases have been made probable as the site of bromosulfophthalein action. It is suggested that bromosulfophthalein acts via the electro-static effects of the increased negative surface charge, making dehydrogenases less accessible for their substrates.