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1 November 2002 An Extracellular monoADP-ribosyl Transferase Activity in Entamoeba histolytica Trophozoites
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Due to the important role of monoADP-ribosyl transferases in physiological and pathological events, we investigated whether the protozoan parasite Entamoeba histolytica had monoADP-ribosyl transferase activity. Reactions were initiated using ameba-free medium as the source of both enzyme and ADP-ribosylation substrate(s) and [32P]NAD as source of ADP-ribose. Proteins were analyzed by electrophoresis, and [32P]-labeled proteins were detected by autoradiography. Using the crude extracellular medium, a major labeled product of Mr 37,000 was observed. The yield of this product was reduced markedly using medium from Brefeldin A-treated trophozoites, indicating that the extracellular monoADP-ribosyl transferase and/or its substrate depended on vesicular transport. The labeling of the 37-kDa substrate was dependent on reaction time, temperature, pH, and the ratio of unlabeled NAD to [32P]NAD . After two purification steps, several new substrates were observed, perhaps due to their enrichment. The reaction measured ADP-ribosylation since [14C-carbonyl]NAD was not incorporated into ameba substrates and a 75-fold molar excess of ADP-ribose caused no detectable inhibition of the monoADP-ribosyl transferase reaction. On the basis of sensitivity to NH2OH, the extracellular monoADP-ribosyl transferase of E. histolytica may be an arginine-specific enzyme. These results demonstrate the existence in E. histolytica of at least one extracellular monoADP-ribosyl transferase, whose localization depends upon a secretion process.

PATRICIA DELGADO-CORONA, GUADALUPE MARTÍNEZ-CADENA, ANGEL H. ALVAREZ, HORACIO E. TORRES-CALZADA, and EVA E. AVILA "An Extracellular monoADP-ribosyl Transferase Activity in Entamoeba histolytica Trophozoites," The Journal of Eukaryotic Microbiology 49(6), 454-459, (1 November 2002).
Received: 8 March 2002; Accepted: 2 September 2002; Published: 1 November 2002

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