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Inactivation of maize NADP-malic enzyme by Cu2+-ascorbate
S E Pinto1, S R Rao, A S Bhagwat
1Molecular Biology and Agriculture Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
Indian Journal of Biochemistry & Biophysics
|August 18, 2012
Summary
Cupric nitrate and ascorbate rapidly inactivate maize malic enzyme by generating reactive oxygen species. This inactivation involves enzyme cleavage, potentially near the substrate-binding site.
Area of Science:
- Biochemistry
- Plant Physiology
- Enzymology
Background:
- Maize malic enzyme is crucial for plant metabolism.
- Understanding enzyme regulation and inactivation is vital for agricultural applications.
Purpose of the Study:
- To investigate the inactivation mechanism of maize malic enzyme by the cupric ion-ascorbate system.
- To identify the reactive species involved and the effect on enzyme structure.
Main Methods:
- Enzyme activity assays were performed under various conditions.
- Protective agents (L-malate, NADP, EDTA, histidine, imidazole) were used.
- Protease inhibitors and reactive oxygen species scavengers were employed.
- Peptide cleavage analysis using molecular mass determination.
Main Results:
- Cupric nitrate and ascorbate rapidly inactivated maize malic enzyme at pH 5.0.
- Inactivation was prevented by L-malate or NADP, suggesting substrate protection.
- Enzyme cleavage into peptides (55, 48, 38, 14 kDa) occurred during inactivation.
- Reactive oxygen species, including singlet oxygen and H2O2, were implicated.
- Protection by EDTA, histidine, and imidazole indicated metal ion involvement.
Conclusions:
- The cupric ion-ascorbate system generates reactive oxygen species that inactivate maize malic enzyme.
- Inactivation involves enzyme cleavage, likely at or near the substrate-binding site.
- Understanding this inactivation pathway is important for maize enzyme stability and function.
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