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Target size analysis of opioid receptors. No difference between receptor types, but discrimination between two

S Ott, T Costa, M Wüster

    European Journal of Biochemistry
    |March 17, 1986
    PubMed

    Insights

    Opioid receptor target size analysis was clarified using irradiation, revealing a 56 kDa unit. High-affinity binding requires an additional 40-44 kDa membrane component in the absence of specific ions and GTP.

    Area of Science:

    • Pharmacology
    • Biochemistry
    • Neuroscience

    Background:

    • Opioid receptor target size analysis is complex due to multi-exponential inactivation curves.
    • Indirect irradiation effects can cause artifacts in target size analysis.
    • Eliminating these artifacts is crucial for accurate molecular characterization.

    Purpose of the Study:

    • To determine the molecular mass of the opioid receptor binding site.
    • To investigate the influence of ions and GTP on opioid receptor complex size.
    • To elucidate the components necessary for high-affinity opioid binding.

    Main Methods:

    • Irradiation of intact frozen tissue to eliminate inactivation curve artifacts.
    • Assaying opioid binding activity in various conditions (presence/absence of Na+, Mg2+, GTP).
    • Determining molecular mass using inactivation curves.

    Main Results:

    • Irradiation enabled mono-exponential inactivation, revealing a molecular mass of 98 ± 2 kDa.
    • In the presence of Na+, Mg2+, and GTP, the molecular mass was reduced to 56 ± 4.4 kDa.
    • Identical results were observed across different species and cell lines for mu, delta, and kappa opioid binding.

    Conclusions:

    • The opioid recognition site appears to be a 56 kDa unit.
    • An additional 40-44 kDa membrane component is essential for high-affinity opioid binding when Na+, Mg2+, and GTP are absent.
    • This suggests a dynamic complex for opioid receptor function.

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