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Related Experiment Videos

ATP-Dependent Proteolytic Activity from Spinach Leaves.

J B Hammond1, J Preiss

  • 1Department of Biochemistry and Biophysics, University of California, Davis, California 95616.

Plant Physiology
|December 1, 1983
PubMed
Summary
This summary is machine-generated.

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Spinach leaf extracts contain heat-stable factors that inactivate starch phosphorylase enzymes. This inactivation, likely due to proteolysis, is influenced by ATP, Mg(2+), and light conditions during flowering.

Area of Science:

  • Plant Biochemistry
  • Enzymology
  • Molecular Biology

Background:

  • Starch phosphorylase plays a crucial role in carbohydrate metabolism in plants.
  • Regulation of plant enzyme activity is essential for adapting to environmental changes.
  • Previous studies have indicated post-translational modifications can regulate enzyme function.

Purpose of the Study:

  • To investigate the inactivation mechanism of spinach leaf cytoplasmic starch phosphorylase.
  • To identify the factors responsible for phosphorylase inactivation in spinach leaves.
  • To understand the biochemical properties and regulatory conditions of the inactivating factors.

Main Methods:

  • Enzyme assays were performed using spinach leaf cytoplasmic starch phosphorylase and rabbit muscle phosphorylase a.

Related Experiment Videos

  • Partially purified spinach leaf extracts were used to study inactivation.
  • The effects of ATP, Mg(2+), heat, protease inhibitors (p-aminobenzamidine, phenylboronic acid, phenylmethylsulfonyl fluoride, leupeptin), and 5'-adenylate were tested.
  • Casein-degrading activities were measured to identify proteolytic activity.

    • Main Results:

    • Spinach leaf extract inactivated both spinach and rabbit muscle phosphorylase in the presence of ATP and Mg(2+).
    • The inactivating factors were heat-stable but sensitive to protease attack.
    • Inactivation was prevented by specific protease inhibitors and 5'-adenylate.
    • ATP-mediated inactivation was enhanced by Mg(2+), reducing the apparent K(m) for ATP.
    • Casein-degrading activity, consistent with proteolysis, was detected and correlated with inactivation.

    Conclusions:

    • Phosphorylase inactivation in spinach leaves is likely mediated by proteolytic enzymes.
    • The activity of these proteases is regulated by ATP and Mg(2+), and influenced by developmental stage (flowering) and light.
    • Understanding this regulatory mechanism provides insight into plant carbohydrate metabolism control.