These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Surface proton donors for the D-pathway of cytochrome c oxidase in the absence of subunit III.
    Author: Adelroth P, Hosler J.
    Journal: Biochemistry; 2006 Jul 11; 45(27):8308-18. PubMed ID: 16819830.
    Abstract:
    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.
    [Abstract] [Full Text] [Related] [New Search]