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Two forms of NADP-dependent malic enzyme in expanding maize leaves.

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Purification of the Sarco-Endoplasmic Reticulum Ca2+-ATPase from Rabbit Muscle
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A possible plasma membrane particle containing malic enzyme activity.

P Pupillo1, E Del Grosso

  • 1Istituto Botanico, Università di Bologna, Via Irnerio 42, I-40126, Bologna, Italy.

Planta
|December 5, 2013
PubMed
Summary

Researchers identified a plasma membrane fraction containing NADP-dependent malic enzyme in plant tissues. This enzyme

Area of Science:

  • Plant biochemistry
  • Cell biology
  • Membrane protein analysis

Background:

  • NADP-dependent malic enzyme (malate dehydrogenase) is a key enzyme in plant metabolism.
  • Its localization within plant cells is not fully understood, particularly its association with cellular membranes.

Purpose of the Study:

  • To identify and characterize the cellular location of NADP-dependent malic enzyme activity in plant tissues.
  • To investigate the properties of the enzyme when associated with cellular membranes.

Main Methods:

  • Isolation and characterization of membrane fractions from plant tissues (Cucurbita hypocotyls, maize coleoptiles).
  • Enzyme assays for NADP-dependent malic enzyme activity.
  • Sucrose gradient centrifugation and analysis of enzyme markers.

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  • Assessment of enzyme binding stability and release under various conditions (salts, EDTA, Triton-X-100, hypotonic treatment).

    • Main Results:

    • A distinct membrane fraction containing significant NADP-dependent malic enzyme activity (up to 10% of total activity) was isolated.
    • This fraction, termed the "malic enzyme particle," was identified as the plasma membrane based on sedimentation, density, enzyme markers, and Metrizamide penetration.
    • The enzyme binding to the plasma membrane was stable but could be released by Triton-X-100 or hypotonic conditions, suggesting vesicle formation during homogenization.
    • Low malic enzyme activities were also found associated with proplastids.

    Conclusions:

    • NADP-dependent malic enzyme is localized to the plasma membrane in plant tissues.
    • The enzyme is stably bound to the plasma membrane, likely within osmotically sensitive vesicles formed during tissue homogenization.
    • This finding provides new insights into the subcellular distribution and potential roles of malic enzyme in plant cells.