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Protein kinase activity and endogenous phosphorylation in subfractions of rat liver mitochondria

T Henriksson, B Jergil

    Biochimica Et Biophysica Acta
    |December 11, 1979
    PubMed

    Insights

    This study reveals that most protein kinase activity in rat liver mitochondria resides in the intermembrane space, with distinct cyclic AMP-dependent and independent enzymes identified. Phosphate incorporation was highest in the outer mitochondrial membrane.

    Area of Science:

    • Mitochondrial biochemistry
    • Enzymology
    • Cellular signaling

    Background:

    • Mitochondria possess complex enzymatic machinery.
    • Protein kinases play crucial roles in cellular regulation.
    • Understanding mitochondrial enzyme localization is key to deciphering cellular processes.

    Purpose of the Study:

    • To subfractionate rat liver mitochondria and characterize protein kinase activity.
    • To investigate the localization and properties of mitochondrial protein kinases.
    • To analyze endogenous phosphate incorporation in mitochondrial fractions.

    Main Methods:

    • Rat liver mitochondria were subfractionated into outer membrane, intermembrane, and mitoplast fractions.
    • Protein kinase activity was assayed and stimulated by cyclic AMP.
    • Enzymes were resolved using DEAE-cellulose chromatography.
    • Endogenous phosphate incorporation was measured in different mitochondrial fractions.

    Main Results:

    • 80-90% of protein kinase activity was localized to the intermembrane fraction.
    • Intermembrane kinase activity was cyclic AMP-stimulated; mitoplast activity required Triton X-100 treatment.
    • Three protein kinase peaks were identified, including a cyclic AMP-dependent catalytic subunit and type II enzyme.
    • High endogenous phosphate incorporation occurred in the outer mitochondrial membrane and mitoplasts.

    Conclusions:

    • Rat liver mitochondria harbor distinct protein kinase populations in the intermembrane space and mitoplasts.
    • Specific protein kinase activities are differentially regulated and localized within mitochondria.
    • Mitochondrial outer membranes exhibit significant endogenous phosphorylation activity.

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