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The human leukocyte photoreactivating enzyme.

B M Sutherland

    Basic Life Sciences
    |January 1, 1975
    PubMed
    Summary

    Human leukocytes contain a photoreactivating enzyme that repairs ultraviolet-damaged DNA using visible light. This discovery allows for direct testing of DNA damage

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    Area of Science:

    • Molecular biology
    • Biochemistry
    • Photobiology

    Background:

    • Ultraviolet (UV) radiation induces DNA damage, primarily cyclobutane pyrimidine dimers.
    • DNA repair mechanisms are crucial for maintaining genomic integrity and preventing disease.
    • Photoreactivating enzymes (PREs) are known to directly reverse pyrimidine dimers using light energy.

    Purpose of the Study:

    • To isolate and characterize a photoreactivating enzyme from human leukocytes.
    • To understand the enzymatic properties and requirements of human PRE.
    • To explore the implications of human PRE for studying UV-induced DNA damage and abnormal cell growth.

    Main Methods:

    • Isolation and purification of photoreactivating enzyme from human leukocytes.
    • Enzymatic assays using UV-irradiated DNA as substrate.
    • Characterization of enzyme properties including substrate specificity, cofactor requirements, and optimal conditions (pH, ionic strength).
    • Determination of apparent molecular weight.

    Main Results:

    • Successfully isolated and characterized a photoreactivating enzyme from human leukocytes.
    • The enzyme utilizes UV-irradiated DNA (220-300 nm) and visible light (300-600 nm) for catalysis.
    • It efficiently converts cyclobutane pyrimidine dimers to monomer pyrimidines.
    • Apparent monomer molecular weight is 40,000, with a tendency to aggregate.
    • Optimal pH is 7.2, no metal ions required, and optimal ionic strength is 0.05.

    Conclusions:

    • Human cells possess a functional photoreactivating enzyme.
    • The characterized human PRE shares similarities with the Escherichia coli enzyme but has a distinct ionic strength optimum.
    • The presence of this enzyme in humans opens avenues for directly assessing the role of pyrimidine dimers in abnormal cell growth, such as cancer.

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