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Published on: October 25, 2021

Membrane effects on hepatic microsomal glucose-6-phosphatase

M Gratzl

    Hoppe-Seyler'S Zeitschrift Fur Physiologische Chemie
    |June 1, 1975
    PubMed

    Insights

    Rat liver microsomes show weak galactose 6-phosphate hydrolysis. This suggests glucose-6-phosphatase also processes galactose 6-phosphate, with a specific carrier for glucose 6-phosphate in the microsomal membrane.

    Area of Science:

    • Biochemistry
    • Cell Biology
    • Enzymology

    Background:

    • Rat liver microsomes possess enzymes for substrate hydrolysis.
    • Galactose 6-phosphate is a substrate whose interaction with microsomal enzymes is not fully understood.
    • Glucose-6-phosphatase is a key enzyme in carbohydrate metabolism within the endoplasmic reticulum.

    Purpose of the Study:

    • To investigate the hydrolyzing activity of rat liver microsomes towards galactose 6-phosphate.
    • To determine the relationship between galactose 6-phosphate and glucose-6-phosphatase activity.
    • To explore the transport mechanisms of substrates and products across the microsomal membrane.

    Main Methods:

    • Enzymatic assays using rat liver microsomes (intact and disrupted).
    • Kinetic analysis to determine kinetic parameters (Km, Vmax) for galactose 6-phosphate hydrolysis.
    • Competitive inhibition studies using glucose-6-phosphatase as a reference enzyme.

    Main Results:

    • Rat liver microsomes exhibit weak galactose 6-phosphate hydrolyzing activity.
    • Disruption of microsomal vesicles increased the maximum velocity (Vmax) but not the Michaelis constant (Km) for galactose 6-phosphate.
    • Galactose 6-phosphate competitively inhibited glucose-6-phosphatase, indicating hydrolysis by the same enzyme.
    • Higher latency for galactose 6-phosphate hydrolysis compared to glucose 6-phosphate suggests a carrier for glucose 6-phosphate.

    Conclusions:

    • Rat liver microsomes possess a low activity for galactose 6-phosphate hydrolysis, likely mediated by glucose-6-phosphatase.
    • The data suggest the presence of a specific carrier for glucose 6-phosphate in the microsomal membrane.
    • The product, glucose, can likely penetrate the microsomal membrane, as it is not retained intracellularly.

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