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Dependence of Trichomonas vaginalis upon polyamine backconversion

Haskins Laboratories¹ and Department of Chemistry and Physical Sciences², Pace University, 41 Park Row, New York, NY 10038, USA
Department of Biology, St Francis College, 180 Remsen Street, Brooklyn, NY 11201, USA³
Grace Cancer Drug Center, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA⁴

Author for correspondence: Nigel Yarlett. Tel: +1 212 346 1246. Fax: +1 212 346 1586. e-mail: nyarlett{at}pace.edu

Trichomonas vaginalis grown for 16 h in the presence of [¹⁴C]spermine formed a high intracellular pool of [¹⁴C]spermidine and a small but detectable pool of [¹⁴C]putrescine. When [³H]putrescine was added to the growth medium, a large intracellular pool of [³H]putrescine was found, but it was not further metabolized, confirming previous studies suggesting the absence of a forward-directed polyamine synthetic pathway in T. vaginalis. Spermidine:spermineN₁-acetyltransferase (SSAT) and polyamine oxidase enzyme activities were detected which collectively converted spermine to spermidine. Polyamine oxidase was localized in the hydrogenosome-enriched fraction, whereas SSAT was found predominantly in the cytosolic fraction. In the presence of saturating substrate, the trichomonad SSAT had an activity of 0·39±0·09 nmol min^-1 (mg protein)^-1 (the mean of five analyses) and an apparent K_m for spermine of 1·7 µM. The enzyme was competitively inhibited by di(ethyl)norspermine with a K_i of 28 µM. Growth studies indicated that 50 µM di(ethyl)norspermine caused a 68% and 84% reduction in the intracellular concentrations of spermidine and spermine, respectively. The trichomonad polyamine oxidase required FAD as a cofactor and had an apparent K_m of 6·0 µM forN¹-acetylspermine. The potential of bis(alkyl) polyamine analogues as antitrichomonad agents is discussed.

Keywords: Polyamines, Trichomonas, polyamine oxidation, acetylated polyamines

Abbreviations: DENSpm, di(ethyl)norspermine; ODC, ornithine decarboxylase; SSAT, spermidine:spermine N¹-acetyltransferase

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