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Related Experiment Videos

Conformational integrity of human alpha-thrombin.

G B Villanueva, V Perret, J W Fenton

    Thrombosis Research
    |December 1, 1984
    PubMed
    Summary
    This summary is machine-generated.

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    Storage at pH 6 stabilizes human alpha-thrombin. Structural changes, specifically in aromatic regions and involving histidine ionization, occur at pH 6.0, impacting enzyme stability and efficiency.

    Area of Science:

    • Biochemistry
    • Protein Chemistry
    • Enzymology

    Background:

    • Human alpha-thrombin exhibits increased stability at pH 6.
    • Understanding conformational changes is key to explaining pH-dependent stability.
    • Previous studies suggest pH influences thrombin's structure and function.

    Purpose of the Study:

    • To investigate structural alterations in human alpha-thrombin at pH 6.0 versus pH 7.5.
    • To correlate structural changes with observed stabilization at lower pH.
    • To identify specific residues involved in pH-dependent conformational shifts.

    Main Methods:

    • Circular dichroism (CD) spectroscopy (peptide and aromatic regions).
    • Difference spectroscopy and thermal stability assays.
    • Chemical modification using specific reagents (e.g., dimethyl-(2-hydroxy-5-nitrobenzyl)sulfonium bromide) and solvent perturbation studies.

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    Main Results:

    • No significant differences in secondary structure (CD peptide transition, thermal stability) were observed between pH 6.0 and 7.5.
    • Alterations in the aromatic region (300-250 nm CD) indicated changes in the microenvironment of aromatic residues.
    • Fewer tryptophan and tyrosine residues were solvent-accessible at pH 6.0 compared to pH 7.5.
    • A specific histidine ionization (midpoint pH 6.45) correlated with spectral changes, suggesting involvement of a non-active site histidine.

    Conclusions:

    • pH 6.0 induces conformational changes in human alpha-thrombin, distinct from secondary structure alterations.
    • A histidine residue, separate from the active site His-43, ionizes around pH 6.45, driving these conformational shifts.
    • The ionization of this histidine and associated conformational changes likely contribute to the reduced catalytic efficiency and stability of alpha-thrombin at pH 6.