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L-Asparagainases from Citrobacter freundii.

L Davidson, M Burkom, S Ahn

    Biochimica Et Biophysica Acta
    |January 11, 1977
    PubMed
    Summary
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    Researchers identified three L-asparagine-hydrolyzing enzymes in Citrobacter freundii. One enzyme, asparaginase A, is stable, has high affinity for L-asparagine, and extended survival in lymphoma-bearing mice.

    Area of Science:

    • Microbiology
    • Enzymology
    • Biochemistry

    Background:

    • L-asparagine is crucial for certain cancer cells.
    • Enzymes that hydrolyze L-asparagine, like asparaginase, are used in cancer therapy.
    • Understanding microbial sources of asparaginase is important for therapeutic development.

    Purpose of the Study:

    • To identify and characterize L-asparagine-hydrolyzing enzymes in Citrobacter freundii.
    • To evaluate the therapeutic potential of these enzymes, particularly in a tumor model.

    Main Methods:

    • Enzyme extraction and identification from Citrobacter freundii.
    • Characterization of enzyme properties: stability, sensitivity to inhibitors (p-chloromercuribenzoate, dithiothreitol), and substrate affinity (Km).
    • Purification of a specific enzyme (asparaginase A) to homogeneity.

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  • In vivo testing of purified asparaginase A in a mouse lymphoma model (C3H/HE mice with 6C3HED lymphoma).

    • Main Results:

    • Three distinct L-asparagine-hydrolyzing enzymes were identified.
    • One enzyme, asparaginase-glutaminase (EC 3.5.1.1), was labile and sensitive to mercurials.
    • Asparaginase B was sensitive to mercurials but protected by dithiothreitol, with low L-asparagine affinity.
    • Asparaginase A was stable, insensitive to mercurials, had high L-asparagine affinity (Km = 2.9 x 10^-5 M), and was purified (MW ~140,000).
    • Purified C. freundii asparaginase A significantly increased survival time in tumor-bearing mice.

    Conclusions:

    • Citrobacter freundii possesses multiple L-asparagine-hydrolyzing enzymes with distinct properties.
    • Asparaginase A is a stable, high-affinity enzyme with demonstrated anti-tumor efficacy in a preclinical model.
    • This enzyme warrants further investigation as a potential therapeutic agent for asparagine-dependent cancers.