S-adenosylmethionine and Pneumocystis carinii.
We previously reported that S-adenosylmethionine (AdoMet), a key molecule in methylation reactions and polyamine biosynthesis, enhances axenic culture of the AIDS-associated opportunistic fungal pathogen Pneumocystis carinii. Here we report that AdoMet is absolutely required for continuous growth. Two transporters are present, one high affinity, K(m) = 4.5 microm, and one low affinity, K(m) = 333 microm. The physiologically relevant high affinity transporter has a pH optimum of 7.5 and no related natural compounds compete for uptake. Transport is 98% inhibited at 4 degrees C, 24% inhibited by 20 mm sodium azide, and 95% inhibited by the combination of 20 mm sodium azide and 1 mm salicylhydroxamic acid; thus transport is active and dependent on both a cytochrome chain and an alternative oxidase. In vitro, AdoMet is used at a rate of 1. 40 x 10(7) molecules cell(-1) min(-1). AdoMet synthetase activity was not detected by a sensitive radiolabel incorporation assay capable of detecting 0.1% of the activity in rat liver. In addition, the AdoMet plasma concentration of rats is inversely correlated with the number of P. carinii in the lungs. These findings demonstrate that P. carinii is an AdoMet auxotroph. The uptake and metabolism of this compound are rational chemotherapeutic targets.
Merali
S
S
Department of Medical and Molecular Parasitology, New York University School of Medicine, New York, New York 10010, USA. merals01@popmail.med.nyu.edu
Vargas
D
D
Franklin
M
M
Clarkson
A B
AB
D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D003470:Culture Media; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008168:Lung / Q000382:microbiology; D011010:Pneumocystis / Q000254:growth & development* / Q000378:metabolism*; D011020:Pneumonia, Pneumocystis / Q000097:blood / Q000382:microbiology*; D051381:Rats; D012436:S-Adenosylmethionine / Q000097:blood / Q000378:metabolism*; D012457:Salicylamides / Q000494:pharmacology; D019810:Sodium Azide / Q000494:pharmacology
D003470:Culture Media; D012457:Salicylamides; D012436:S-Adenosylmethionine; C005703:salicylhydroxamic acid; D019810:Sodium Azide