期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 104, 期 2, 页码 519-524出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0606369104
关键词
photosynthesis; electron transfer; quinone reduction; spin-spin interaction
X-band EPR features in the region of 90-150 mT have previously been attributed to heme c(i) of the b(6) complex [Zhang H, Primak A, Bowman MK, Kramer DIM, Cramer WA (2004) Biochemistry 43:16329-16336] and interpreted as arising from a high-spin species. However, the complexity of the observed spectrum is rather untypical for high-spin hemes. In this work, we show that addition of the inhibitor 2-n-nonyl-4-hydroxyquinoline N-oxide largely simplifies heme ci's EPR properties. The spectrum in the presence of 2-n-nonyl-4-hydroxyquinoline N-oxide is demonstrated to be caused by a simple S 5/2, rhombic species split by magnetic dipolar interaction (A(xx) 7.5 mT) with neighboring heme b(H). The large spacing of lines in the uninhibited system, by contrast, cannot be rationalized solely on the basis of magnetic dipolar coupling but is likely to encompass strong contributions from exchange interactions. The role of the H2O/OH- molecule bridging heme ci's Fe atom and heme b(H)'S propionate side chain in mediating these interactions is discussed.
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