Activation of NADP-malate dehydrogenase in C3 plants by reduced glutathione

Abstract

NADP-malate dehydrogenase extracted from darkened leaves of the C3 plants pea, barley, wheat and spinach was activated by reduced glutathione, a monothiol, as well as by dithiothreitol (DTT). However, in the C4 plants maize and Flaveria trinervia, only dithiothreitol could effectively activate the enzyme. There was no activation of the maize enzyme and little or no activation of the F. trinervia enzyme by glutathione. The failure of glutathione to activate NADP-MDH in leaf extracts of maize and F. trinervia may indicate there is some difference in disulfide groups of the protein compared to the C3 plant enzyme. Both DTT and glutathione could activate NADP-malate dehydrogenase in a partially purified enzyme preparation from pea leaves with or without addition of partially purified thioredoxin. However, the required concentration of reductant was lower with addition of thioredoxin than in its absence. In extracts of C3 species and the partially purified pea enzyme the level of activation after 40 to 60 min under aerobic conditions was higher (up to twofold) with DTT than with glutathione. Under anaerobic conditions, the initial rate of activation was about twice as high with DTT as with glutathione, but the total activation after 40 to 60 min was similar. Ascorbate was totally ineffective as a reducing agent in activating NADP-MDH from C3 or C4 plants, possibly due to its more positive redox potential.

Involvement of AsA/DHA and GSH/GSSG Ratios in Gene and Protein Expression and in the Activation of Defence Mechanisms Under Abiotic Stress Conditions

“…A different hypothesis concerning the role of light stress on GSH was addressed. For example, it was stated that GSSG might act as a molecule that inactivates light-modulated stromal enzymes such as fructose 1,6-bisphosphatase through an oxidation of their -SH groups (Alscher 1989;Vivekanandan and Edwards 1987). According to Baena-Gonzalez et al (2001), high light intensity causes an elevation of the GSH/GSSG ratio, an effect that has as a consequence the inactivation of the plastid transcription kinase (PTK), an enzyme that was found to respond to changes in thiol/disulfide redox state mediated by glutathione (Link et al 1997), and this inactivation causes changes in the phosphorylation of RNA polymerase subunits leading to an elevation of transcriptional activity.…”

Biosynthesis and antioxidant function of glutathione in plants

“…However, it was shown subsequently by Foyer and Haliiwell (1978) in vivo that in the dark GSSG levels never rose to a point where sueh an oxidatioo could occur. Some interesting new results suggest that DOCUMENTED CONSEQUENCES OF OXIDATIVE STRESS the reverse is possible and that GSH may act to activate at least one light-modtilated enzyme (Vivekanandan and Edwards 1987). Concentrations of GSH in the 3-10 mM range brought about substantial activation of partially purified NADP-MDH from pea.…”

Regulation of 2-carboxy-D-arabinitol 1-phosphate phosphatase: activation by glutathione and interaction with thiol reagents

“…This has been observed in itro with NADP-dependent malate dehydrogenase from pea, either in native [20] or truncated form [21]. In addition, a direct activation of malate dehydrogenase by GSH was previously reported using partially purified enzyme from several other species of C $ plants, including barley, spinach and wheat [22].…”