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ADP-ribosyltransferase in Plasmodium (malaria parasites)
Abstract:
The nuclei of Plasmodium yoelii nigeriensis contain an enzyme, ADP-ribosyltransferase, that will incorporate the ADP-ribose moiety of NAD+ into acid-insoluble product. The time, pH and temperature optima of this incorporation are 30 min, 8.5 and 25 degrees C respectively. Maximum stimulation of the enzyme activity is obtained with 1.0 mM-dithiothreitol or 2.0 mM-2-mercaptoethanol. Ca2+ and Mg2+ ions at optimum concentrations of 5 mM and 10 mM respectively stimulated the activity of the enzyme by 21% and 91%. The enzyme activity is, however, inhibited by 24% in the presence of 10 mM-MnSO4. The substrate, NAD+, exhibits an apparent Km of 500 microM, and the activity of the enzyme is inhibited by four chemical classes of inhibitors: nicotinamides, methylxanthines, thymidine and aromatic amides. The inhibitors are effective in the following increasing order: nicotinamide less than 3-aminobenzamide less than thymidine less than 5-methylnicotinamide less than theophylline less than m-methoxybenzamide less than theobromine. The enzyme activity is also inhibited by some DNA-binding anti-malarial drugs.
Insights
Plasmodium yoelii nigeriensis nuclei contain an ADP-ribosyltransferase enzyme. This enzyme incorporates ADP-ribose from NAD+ and is modulated by various ions and inhibited by specific chemical compounds and DNA-binding antimalarial drugs.
Area of Science:
- Biochemistry
- Parasitology
- Molecular Biology
Background:
- Plasmodium yoelii nigeriensis is a parasite that causes malaria in rodents.
- Understanding parasitic enzymes is crucial for developing new antimalarial drugs.
- ADP-ribosyltransferases (ARTs) play roles in various cellular processes, including DNA repair and gene regulation.
Purpose of the Study:
- To characterize the ADP-ribosyltransferase enzyme found in the nuclei of Plasmodium yoelii nigeriensis.
- To investigate the enzyme's optimal reaction conditions and substrate kinetics.
- To identify potential inhibitors of the enzyme, including chemical compounds and antimalarial drugs.
Main Methods:
- Enzyme activity assays were performed to determine optimal conditions (time, pH, temperature).
- The effects of various ions (dithiothreitol, 2-mercaptoethanol, Ca2+, Mg2+, Mn2+) on enzyme activity were assessed.
- Kinetic parameters (Km) for the substrate NAD+ were determined.
- Inhibition studies were conducted using a range of chemical compounds and DNA-binding antimalarial drugs.
Main Results:
- The enzyme's optimal activity was observed at 30 minutes, pH 8.5, and 25°C.
- Dithiothreitol and 2-mercaptoethanol significantly stimulated enzyme activity.
- Ca2+ and Mg2+ ions enhanced activity, while Mn2+ inhibited it.
- The apparent Km for NAD+ was 500 μM.
- The enzyme was inhibited by nicotinamides, methylxanthines, thymidine, and aromatic amides in a specific order.
- DNA-binding antimalarial drugs also demonstrated inhibitory effects.
Conclusions:
- The characterized ADP-ribosyltransferase from Plasmodium yoelii nigeriensis exhibits specific kinetic and regulatory properties.
- The enzyme's sensitivity to various inhibitors suggests potential therapeutic targets for antimalarial drug development.
- Further investigation into the role of this enzyme in parasite biology could reveal novel strategies for malaria control.