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Related Experiment Videos

Radiation-damaged tyrosinase molecules are inactive.

E S Kempner1, J H Miller

  • 1Laboratory of Physical Biology, National Institutes of Health, Bethesda, Maryland 20892.

Biophysical Journal
|January 1, 1989
PubMed
Summary

Radiation inactivation studies reveal distinct target sizes for mushroom tyrosinase's diphenoloxidase and monophenoloxidase activities, corresponding to its H and HL2 subunits. Fragments showed no activity, supporting target theory principles.

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Area of Science:

  • Biochemistry
  • Enzymology
  • Radiation Biology

Background:

  • Mushroom tyrosinase is a key enzyme in melanin biosynthesis.
  • Understanding its subunit structure and function is crucial for various applications.
  • Radiation inactivation is a technique used to determine the molecular size of enzymes in situ.

Purpose of the Study:

  • To determine the target sizes of diphenoloxidase and monophenoloxidase activities of mushroom tyrosinase using radiation inactivation.
  • To correlate these target sizes with the enzyme's subunit composition.
  • To validate the applicability of target theory to mushroom tyrosinase.

Main Methods:

  • Enzyme samples were subjected to radiation inactivation.
  • Activity assays were performed to measure diphenoloxidase and monophenoloxidase activities.

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  • Irradiated samples underwent gel electrophoresis to analyze protein fragments and their associated activity.

    • Main Results:

    • Different target sizes were obtained for diphenoloxidase and monophenoloxidase activities.
    • These target sizes corresponded to the H and HL2 (or HL) subunits of mushroom tyrosinase.
    • No detectable activity was found in the radiolytic fragments after gel electrophoresis.

    Conclusions:

    • Mushroom tyrosinase likely functions as a multimeric enzyme with distinct subunits responsible for different activities.
    • The H subunit is associated with diphenoloxidase activity, while the HL2 (or HL) subunit is linked to monophenoloxidase activity.
    • The results are consistent with the fundamental assumptions of target theory in enzyme inactivation studies.