PMID- 23618787
OWN - NLM
STAT- MEDLINE
DCOM- 20130808
LR  - 20161126
IS  - 0006-3002 (Print)
IS  - 0006-3002 (Linking)
VI  - 1827
IP  - 7
DP  - 2013 Jul
TI  - Why is the reduction of NO in cytochrome c dependent nitric oxide reductase 
      (cNOR) not electrogenic?
PG  - 826-33
LID - S0005-2728(13)00076-5 [pii]
LID - 10.1016/j.bbabio.2013.04.005 [doi]
AB  - The membrane-bound enzyme cNOR (cytochrome c dependent nitric oxide reductase) 
      catalyzes the reduction of NO in a non-electrogenic process. This is in contrast 
      to the reduction of O2 in cytochrome c oxidase (CcO), the other member of the 
      heme-copper oxidase family, which stores energy by the generation of a membrane 
      gradient. This difference between the two enzymes has not been understood, but it 
      has been speculated to be of kinetic origin, since per electron the NO reduction 
      is more exergonic than the O2 reduction, and the energy should thus be enough for 
      an electrogenic process. However, it has not been clear how and why 
      electrogenicity, which mainly affects the thermodynamics, would slow down the 
      very exergonic NO reduction. Quantum chemical calculations are used to construct 
      a free energy profile for the catalytic reduction of NO in the active site of 
      cNOR. The energy profile shows that the reduction of the NO molecules by the 
      enzyme and the formation of N2O are very exergonic steps, making the rereduction 
      of the enzyme endergonic and rate-limiting for the entire catalytic cycle. 
      Therefore the NO reduction cannot be electrogenic, i.e. cannot take electrons and 
      protons from the opposite sides of the membrane, since it would increase the 
      endergonicity of the rereduction when the gradient is present, thereby increasing 
      the rate-limiting barrier, and the reaction would become too slow. It also means 
      that proton pumping coupled to electron transfer is not possible in cNOR. In CcO 
      the corresponding rereduction of the enzyme is very exergonic.
CI  - Copyright (c) 2013 Elsevier B.V. All rights reserved.
FAU - Blomberg, Margareta R A
AU  - Blomberg MR
AD  - Department of Organic Chemistry, Stockholm University, Stockholm, Sweden. 
      mb@organ.su.se
FAU - Siegbahn, Per E M
AU  - Siegbahn PE
LA  - eng
PT  - Journal Article
DEP - 20130423
PL  - Netherlands
TA  - Biochim Biophys Acta
JT  - Biochimica et biophysica acta
JID - 0217513
RN  - 0 (Hydroquinones)
RN  - 31C4KY9ESH (Nitric Oxide)
RN  - 9007-43-6 (Cytochromes c)
RN  - EC 1.- (Oxidoreductases)
RN  - EC 1.16.- (copper oxidase)
RN  - EC 1.7.2.5 (nitric-oxide reductase)
RN  - EC 1.9.3.1 (Electron Transport Complex IV)
RN  - S88TT14065 (Oxygen)
SB  - IM
MH  - Catalysis
MH  - Catalytic Domain
MH  - Cytochromes c/chemistry/*metabolism
MH  - Electron Transport
MH  - Electron Transport Complex IV/chemistry/metabolism
MH  - *Electrons
MH  - Hydroquinones/metabolism
MH  - Kinetics
MH  - Models, Molecular
MH  - Nitric Oxide/*chemistry/metabolism
MH  - Oxidoreductases/chemistry/*metabolism
MH  - Oxygen/*metabolism
MH  - Thermodynamics
EDAT- 2013/04/27 06:00
MHDA- 2013/08/09 06:00
CRDT- 2013/04/27 06:00
PHST- 2013/02/13 00:00 [received]
PHST- 2013/03/27 00:00 [revised]
PHST- 2013/04/13 00:00 [accepted]
PHST- 2013/04/27 06:00 [entrez]
PHST- 2013/04/27 06:00 [pubmed]
PHST- 2013/08/09 06:00 [medline]
AID - S0005-2728(13)00076-5 [pii]
AID - 10.1016/j.bbabio.2013.04.005 [doi]
PST - ppublish
SO  - Biochim Biophys Acta. 2013 Jul;1827(7):826-33. doi: 10.1016/j.bbabio.2013.04.005. 
      Epub 2013 Apr 23.