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Related Experiment Videos

ATP requirement for mg chelatase in developing chloroplasts.

A D Pardo1, B M Chereskin, P A Castelfranco

  • 1Department of Botany, University of California, Davis, California 95616.

Plant Physiology
|May 1, 1980
PubMed
Summary

Glutamate acts as a cofactor for Mg-protoporphyrin-IX synthesis by regenerating ATP via mitochondria. Purified plastids require high ATP levels, stimulated by phosphoenolpyruvate and pyruvate kinase, with AMP being inhibitory.

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Area of Science:

  • Plant biochemistry
  • Chlorophyll biosynthesis
  • Enzyme kinetics

Background:

  • Mg-protoporphyrin-IX is a key intermediate in chlorophyll biosynthesis.
  • Previous studies indicated l-glutamate as a cofactor for its synthesis in crude extracts.
  • The precise role of glutamate and energy requirements were not fully elucidated.

Purpose of the Study:

  • To investigate the role of l-glutamate in Mg-protoporphyrin-IX synthesis.
  • To determine the energy requirements for Mg chelatase activity in purified plastids.
  • To characterize the effects of various nucleotides and related compounds on the enzyme.

Main Methods:

  • Enzyme assays using crude plastid pellets and purified plastids from cucumber cotyledons.
  • Measurement of Mg-protoporphyrin-IX synthesis.

Related Experiment Videos

  • Investigation of cofactor requirements, including l-glutamate, ATP, phosphoenolpyruvate, and pyruvate kinase.
  • Assessment of nucleotide (ATP, GTP, UTP, CTP, ITP, ADP, AMP) effects on enzyme activity.

    • Main Results:

    • In crude extracts, l-glutamate supports Mg-protoporphyrin-IX synthesis by providing an ATP regenerating system via contaminating mitochondria.
    • Purified plastids demonstrate Mg chelatase activity that is independent of glutamate but requires high ATP concentrations.
    • Activity in purified plastids is significantly enhanced by phosphoenolpyruvate and pyruvate kinase.
    • ADP showed no effect in the absence of an ATP generating system and slight inhibition with ATP.
    • AMP strongly inhibited the reaction, with 50% inhibition at approximately 3.5 mM.

    Conclusions:

    • Glutamate's role in Mg-protoporphyrin-IX synthesis is indirect, facilitating ATP regeneration in crude preparations.
    • Mg chelatase in purified plastids has strict ATP requirements and is modulated by specific energy-generating systems.
    • AMP acts as a potent inhibitor of Mg chelatase, highlighting the importance of precise nucleotide levels for chlorophyll biosynthesis.