PMID- 16789843
OWN - NLM
STAT- MEDLINE
DCOM- 20060725
LR  - 20071114
IS  - 0031-8655 (Print)
IS  - 0031-8655 (Linking)
VI  - 82
IP  - 3
DP  - 2006 May-Jun
TI  - Photoreactions of cytochrome C oxidase.
PG  - 711-9
AB  - The photoreduction of oxidized bovine heart cytochrome c oxidase (CcO) by visible 
      and UV radiation was investigated in the absence and presence of external 
      reagents. In the former case, the quantum yields for direct photoreduction of 
      heme A (heme a + heme a(3)) were 2.6 +/- 0.5 x 10(-3), 4 +/- 1 x 10(-4), and 4 
      +/- 2 x 10(-6) with pulsed laser irradiation at 266, 355 and 532 nm, 
      respectively. Within experimental uncertainty, the quantum yields did not depend 
      on pulse energy, implying that the mechanism is monophotonic. Irradiation with 
      355 nm light resulted in spectral changes similar to those produced independently 
      by reduction with dithionite, whereby the low-spin heme a and Cu(A) are reduced 
      first. Extended illumination at 355 and 532 nm yielded substantial amounts of 
      reduced heme a(3). Heme decomposition was noted with 266 nm light. In the 
      presence of formate and cyanide ions, which bind at the binuclear heme 
      a(3)/copper center in CcO, irradiation at 355 nm caused selective reduction of 
      only the low-spin heme a and Cu(A). The addition of ferrioxalate ion dramatically 
      increased the efficiency of cytochrome c oxidase photoreduction. The quantum 
      efficiency for heme A reduction was found to be near unity, significantly greater 
      than for other known methods of photoreduction. The active reductant is most 
      likely ferrous iron, and its reduction of the enzyme is thermodynamically driven 
      by the reformation of ferrioxalate in the presence of excess oxalate ion. Other 
      metalloenzymes with redox potentials similar to those of cytochrome c oxidase 
      should be amenable to indirect photoreduction by this method.
FAU - Winterle, John S
AU  - Winterle JS
AD  - Department of Chemistry and Biochemistry, University of California at Santa Cruz, 
      USA.
FAU - Einarsdottir, Olof
AU  - Einarsdottir O
LA  - eng
GR  - GM 53788/GM/NIGMS NIH HHS/United States
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
PL  - United States
TA  - Photochem Photobiol
JT  - Photochemistry and photobiology
JID - 0376425
RN  - EC 1.9.3.1 (Electron Transport Complex IV)
SB  - IM
MH  - Animals
MH  - Cattle
MH  - Electron Transport Complex IV/chemistry/metabolism/*radiation effects
MH  - Oxidation-Reduction
MH  - *Photochemistry
MH  - Ultraviolet Rays
EDAT- 2006/06/23 09:00
MHDA- 2006/07/26 09:00
CRDT- 2006/06/23 09:00
PHST- 2006/06/23 09:00 [pubmed]
PHST- 2006/07/26 09:00 [medline]
PHST- 2006/06/23 09:00 [entrez]
AID - 2005-09-14-RA-684 [pii]
AID - 10.1562/2005-09-14-RA-684 [doi]
PST - ppublish
SO  - Photochem Photobiol. 2006 May-Jun;82(3):711-9. doi: 10.1562/2005-09-14-RA-684.