Photoinitiated Electron Transfer within the Paracoccus denitrificans Cytochrome bc sub(1) Complex: Mobility of the Iron-Sulfur Protein Is Modulated by the Occupant of the Q sub(o) Site

• Published in: Biochemistry (Easton) Vol. 50; no. 48; pp. 10462 - 10472-10462-10472
• Main Authors: Havens, Jeffrey, Castellani, Michela, Kleinschroth, Thomas, Ludwig, Bernd, Durham, Bill, Millett, Francis
• Format: Journal Article
• Language: English
• Published: 06.12.2011
• Subjects: Paracoccus denitrificans
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi200453r

Domain rotation of the Rieske iron-sulfur protein (ISP) between the cytochrome (cyt) b and cyt c sub(1) redox centers plays a key role in the mechanism of the cyt bc sub(1) complex. Electron transfer within the cyt bc sub(1) complex of Paracoccus denitrificans was studied using a ruthenium dimer to rapidly photo-oxidize cyt c sub(1) within 1 mu s and initiate the reaction. In the absence of any added quinol or inhibitor of the bc sub(1) complex at pH 8.0, electron transfer from reduced ISP to cyt c sub(1) was biphasic with rate constants of k sub(1f) = 6300 plus or minus 3000 s super(-1)and k sub(1s) = 640 plus or minus 300 s super(-1) and amplitudes of 10 plus or minus 3% and 16 plus or minus 4% of the total amount of cyt c sub(1) photooxidized. Upon addition of any of the P sub(m) type inhibitors MOA-stilbene, myxothiazol, or azoxystrobin to cyt bc sub(1) in the absence of quinol, the total amplitude increased 2-fold, consistent with a decrease in redox potential of the ISP. In addition, the relative amplitude of the fast phase increased significantly, consistent with a change in the dynamics of the ISP domain rotation. In contrast, addition of the P sub(f) type inhibitors JG-144 and famoxadone decreased the rate constant k sub(1f) by 5-10-fold and increased the amplitude over 2-fold. Addition of quinol substrate in the absence of inhibitors led to a 2-fold increase in the amplitude of the k sub(1f) phase. The effect of QH sub(2) on the kinetics of electron transfer from reduced ISP to cyt c sub(1) was thus similar to that of the P sub(m) inhibitors and very different from that of the P sub(f) inhibitors. The current results indicate that the species occupying the Q sub(o) site has a significant conformational influence on the dynamics of the ISP domain rotation.