title: Uptake and metabolism of S-adenosyl-L-methionine by Leishmania mexicana and Leishmania braziliensis promastigotes.
abstract: Promastigotes of Leishmania mexicana and Leishmania braziliensis incorporate S-adenosyl-L-[3H-methyl]methionine (AdoMet) against a concentration gradient through a saturable system. This concentrative uptake requires metabolic energy and is sensitive to temperature and sulfhydryl reagents such as N-ethyl maleimide. Intracellular AdoMet exchanges with external AdoMet. At steady state, unaltered ADoMet in the intracellular pool is at about a 1800-fold concentration in relation to that found in the external medium. Glucose, galactose and ribose did not stimulate uptake rates. Incorporated AdoMet goes into the soluble AdoMet pool, where a small fraction is metabolized, chiefly into methylthioadenosine, decarboxylated AdoMet and methanol. After a 60 min pulse the radioactivity associated with the [3H]AdoMet incorporated disappears with a half-time of 2 h. Transmethylation reactions were analyzed following [3H]AdoMet incorporation. Fractionation experiments indicate that 45-62% and 30-42% of the radioactivity is incorporated into lipids and protein methyl esters respectively, with 5-14% present in the soluble pool of parasites. Sinefungin or its cyclic derivative (1 and 10 micrograms ml-1) in the incubation medium produces 58% and 64% inhibition of AdoMet incorporation into Leishmania promastigotes. Most transmethylation reactions are inhibited, as there is a 50% decrease in the total radioactivity present in both the base-labile and lipidic fraction, with a parallel increase in the percentage of radioactivity in the soluble pool. Previous results give evidence of the importance of AdoMet in American Leishmania promastigote metabolism.
authors.affiliation: Instituto de Biomedicina, Caracas, Venezuela.
authors.forename: J L
authors.initials: JL
authors.lastname: Avila
authors.forename: M A
authors.initials: MA
authors.lastname: Polegre
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002241:Carbohydrates / Q000494:pharmacology; D007700:Kinetics; D007892:Leishmania braziliensis / Q000187:drug effects / Q000378:metabolism*; D007894:Leishmania mexicana / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D008055:Lipids / Q000032:analysis; D008745:Methylation; D009024:Morphogenesis; D012435:S-Adenosylhomocysteine / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000596:Amino Acids; D002241:Carbohydrates; D008055:Lipids; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine