Open AccessStructure of cytochrome a3-Cua3 couple in cytochrome c oxidase as revealed by nitric oxide binding studies.
Author(s) -
Tom H. Stevens,
Gary W. Brudvig,
David F. Bocian,
Sunney I. Chan
Publication year - 1979
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.76.7.3320
Subject(s) - chemistry , cytochrome , cytochrome c oxidase , electron paramagnetic resonance , heme , cytochrome c , cytochrome c peroxidase , electron transport complex iv , coenzyme q – cytochrome c reductase , stereochemistry , oxidoreductase , crystallography , photochemistry , nuclear magnetic resonance , enzyme , biochemistry , physics , mitochondrion
The addition of NO to oxidized cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) causes the appearance of a high-spin heme electron paramagnetic resonance (EPR) signal due to cytochrome a3. This suggests that NO coordinates to Cu+2a3 and breaks the antiferromagnetic couple by forming a cytochrome a+33-Cu+2a3-NO complex. The intensity of the high-spin cytochrome a3 signal depends on the method of preparation of the enzyme and maximally accounts for 58% of one heme. The effect of N-3 on the cytochrome a+33-Cu+2a3-NO complex is to reduce cytochrome a3 to the ferrous state, and this is followed by formation of a new complex that exhibits EPR signals characteristic of a triplet species. On the basis of optical and EPR results, a NO bridge between cytochrome a+23 and Cu+2a3 is proposed--i.e., cytochrome a+23-NO-Cu+2a3. The half-field transition observed at g = 4.34 in the EPR spectrum of this triplet species exhibits resolved copper hyperfine splittings with [A+2] = 0.020 cm-1, indicating that the Cu+2a3 in the cytochrome a+23-NO-Cu+2a3 complex is similar to a type 2 copper site.