PMID- 16819830
OWN - NLM
STAT- MEDLINE
DCOM- 20060825
LR  - 20131121
IS  - 0006-2960 (Print)
IS  - 0006-2960 (Linking)
VI  - 45
IP  - 27
DP  - 2006 Jul 11
TI  - Surface proton donors for the D-pathway of cytochrome c oxidase in the absence of 
      subunit III.
PG  - 8308-18
AB  - The major proton-transfer pathway into the buried active site of cytochrome c 
      oxidase (CcO) is the D-pathway that begins with the subunit I residue Asp-132 on 
      the inner protein surface (the cytoplasmic surface of the aa3-type CcO of 
      Rhodobacter sphaeroides). Asp-132 is surrounded by residues from both subunits I 
      and III. In the absence of subunit III, CcO retains activity, but the functional 
      characteristics of the D-pathway are significantly altered such that the transfer 
      of protons from Asp-132 into the pathway becomes the rate-limiting step. 
      Determination of the pH-dependence of the rate constant for D-pathway proton 
      uptake during the single-turnover of CcO indicates that the pKa of Asp-132 in the 
      absence of subunit III is approximately 7. The removal of subunit III also allows 
      for alternative surface proton donor/acceptors other than Asp-132. With Asp-132 
      altered to alanine, the rate constant for D-pathway proton uptake is very slow (5 
      s(-1)) in the presence of subunit III. Once subunit III is removed, the proton 
      uptake rate constant increases 80-fold, to 400 s(-1). The pKa associated with 
      this uptake is >10, and the initial proton donor/acceptor in D132A III (-) is 
      proposed to be a water of the D-pathway rather than an amino acid residue. 
      Arachidonic acid (Aa), which stimulates the activity of several D-pathway mutant 
      CcOs, appears to become the initial proton donor/acceptor in the absence of 
      subunit III, whether or not Asp-132 is altered. Aa shifts the pKa of the initial 
      proton donor to 7.6 for both wild-type (WT) III (-) and D132A III (-). The 
      results indicate that subunit III creates a barrier that helps prevent protons 
      from donors other than Asp-132 from directly accessing the internal waters of the 
      D-pathway, while the subunit also provides an environment that increases the rate 
      at which Asp-132 transfers protons into the D-pathway.
FAU - Adelroth, Pia
AU  - Adelroth P
AD  - Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural 
      Sciences, Stockholm University, SE-106 91 Stockholm, Sweden. piaa@dbb.su.se
FAU - Hosler, Jonathan
AU  - Hosler J
LA  - eng
GR  - GM56824/GM/NIGMS NIH HHS/United States
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
PT  - Research Support, Non-U.S. Gov't
PL  - United States
TA  - Biochemistry
JT  - Biochemistry
JID - 0370623
RN  - 0 (Bacterial Proteins)
RN  - 0 (Protein Subunits)
RN  - 0 (Protons)
RN  - 27YG812J1I (Arachidonic Acid)
RN  - 7006-34-0 (Asparagine)
RN  - EC 1.9.3.1 (Electron Transport Complex IV)
RN  - S88TT14065 (Oxygen)
SB  - IM
MH  - Arachidonic Acid/pharmacology
MH  - Asparagine/chemistry/genetics
MH  - Bacterial Proteins/*chemistry/genetics
MH  - Catalysis
MH  - Electron Transport Complex IV/*chemistry/drug effects/genetics
MH  - Hydrogen-Ion Concentration
MH  - Mutation
MH  - Oxidation-Reduction
MH  - Oxygen/chemistry/metabolism
MH  - Protein Conformation
MH  - Protein Subunits/chemistry/genetics
MH  - *Protons
MH  - Rhodobacter sphaeroides/*enzymology
EDAT- 2006/07/06 09:00
MHDA- 2006/08/26 09:00
CRDT- 2006/07/06 09:00
PHST- 2006/07/06 09:00 [pubmed]
PHST- 2006/08/26 09:00 [medline]
PHST- 2006/07/06 09:00 [entrez]
AID - 10.1021/bi0605843 [doi]
PST - ppublish
SO  - Biochemistry. 2006 Jul 11;45(27):8308-18. doi: 10.1021/bi0605843.