Conjugation of 2,6-dichloroindophenol with mitochondrial thiol groups.

Substantial quantities of 2,6-dichloroindophenol are bound to mitochondrial constituents. It is likely that binding is mediated by conjugation of dye to thiol groups, since reaction conditions favoring binding are completely analogous to conditions favorable for the conjugation of dye to isolated thiol compounds. Thus, procedures which promote the maintenance of reduced 2,6-dichloroindophenol (addition of DL-/?-hydroxybutyrate, KCN, antimycin A, rotenone, or ascorbate) inhibited the rate of conjugation. Addition of 2,4-dinitrophenol favored the formation of oxidized dye and concomitantly promoted conjugation. The conjugation of dye was completely inhibited by addition of an amount of P-hydroxymercuribenzoate which corresponded well with the thiol content of mitochondria reported by others. Conjugation of dye with thiol groups readily accounts for certain inhibitory effects reported by others and indicates that 2,6-dichlorolndophenol may alter the properties of native systems. Thus much caution is warranted in the interpretation of studies in which 2,6-dichloroindophenol, and other actual or potential quinoids are used.