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Effect of cadmium and glutathione on malic enzyme activity in brown shrimps (Crangon crangon) from the Gulf of Gdańsk

Niedźwiecka N., Mika A., Białk-Bielińska A., Stepnowski P., Skorkowski E.F.

Oceanologia

2011

No. 53 (3)

793-805

The high level of cadmium in the abdominal muscle of the brown shrimp Crangon crangon is due to the serious pollution of the water in the Gulf of Gdańsk. The inhibition of malic enzyme (ME) activity by cadmium, and in consequence the reduced formation of NADPH, could interfere with cellular mechanisms for detoxifying the organism and reducing oxidative stress. The reduced glutathione (GSH) concentration in the abdominal muscle of C. crangon was calculated to be 5.8 mM. The objective of this study was to evaluate the part played by GSH in the effect of cadmium on the activity of NADP-dependent malic enzyme from abdominal muscles of brown shrimps. This enzyme is activated by certain divalent cations (Mg, Mn). The results demonstrate that cadmium inhibits ME activity from shrimp muscle, and that GSH and albumin can reduce this cadmium-inhibited NADP-dependent malic enzyme activity.

Multiple isotope effects as a probe of the tartrate dehydrogenase-catalyzed oxidative decarboxylation of D-malate

Karsten W., Cook P.

Nukleonika

2002

Vol. 47,suppl.1

13-15

A change in the dinucleotide reactant from NAD+ to the more oxidizing APAD+ in the malic enzyme reaction results in a change in the mechanism of oxidative decarboxylation of malate from stepwise to concerted [7]. In order to determine whether this is a phenomenon general to metal ion dependent â-hydroxyacid oxidative decarboxylases, tartrate dehydrogenase, which catalyzes a reaction diastereotopic to malic enzyme, was studied using the technique of multiple isotope effects. A primary deuterium isotope effect of 1.41 on V/Kmalate was measured, as well as a primary 13C-isotope effect of 1.0096. A decrease in the measured value of the 13C-isotope effect to 1.0078 is consistent with a stepwise mechanism, as observed for malic enzyme. The 13C-isotope effect with thioNAD+ also decreases from a value of 1.0053 using D-malate to 1.0009 using D-malate-2-D, consistent with stepwise oxidative decarboxylation with this alternative dinucleotide substrate. The data suggest that the change