ANTIMYCIN INHIBITION OF THE CYTOCHROME BD COMPLEX FROM AZOTOBACTER-VINELANDII INDICATES THE PRESENCE OF A BRANCHED ELECTRON-TRANSFER PATHWAY FOR THE OXIDATION OF UBIQUINOL

Antimycin A and UHBDT inhibit the activity of the purified cytochrome bd complex from Azotobacter vinelandii. Inhibition of activity is non- competitive and antimycin A binding induces a shift to the red in the spectrum of a b-type haem. No inhibitory effects were seen with myxoth iazol. Steady-state experiments indicate that the site of inhibition f or antimycin A lies on the low-potential side of haem b(558). In the p resence of antimycin A at concentrations sufficient to inhibit respira tion, some direct electron transfer from ubiquinol-1 to haem b(595) an d haem d still occurs. The results are consistent with a branched elec tron transfer pathway from ubiquinol to the oxygen reduction site. Abs tract