Document Detail


Ammonia permeability of the aquaglyceroporins from Plasmodium falciparum, Toxoplasma gondii and Trypansoma brucei.
MedLine Citation:
PMID:  16889642     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Plasmodium falciparum uses amino acids from haemoglobin degradation mainly for protein biosynthesis. Glutamine, however, is mostly oxidized to 2-oxoglutarate to restore NAD(P)H + H+. In this process two molecules of ammonia are released. We determined an ammonia production of 9 mmol h(-1) per litre of infected red blood cells in the early trophozoite stage. External application of ammonia yielded a cytotoxic IC50 concentration of 2.8 mM. As plasmodia cannot metabolize ammonia it must be exported. Yet, no biochemical or genomic evidences exist that plasmodia possess classical ammonium transporters. We expressed the P. falciparum aquaglyceroporin (PfAQP) in Xenopus laevis oocytes and examined whether it may serve as an exit pathway for ammonia. We show that injected oocytes: (i) acidify the medium due to ammonia uptake, (ii) take up [14C]methylamine and [14C]formamide, (iii) swell in solution with formamide and acetamide and (iv) display an ammonia-induced NH4+-dependent clamp current. Further, a yeast strain lacking the endogenous aquaglyceroporin (Fps1) is rescued by expression of PfAQP which provides for the efflux of toxic methylamine. Ammonia permeability was similarly established for the aquaglyceroporins from Toxoplasma gondii and Trypanosoma brucei. Apparently, these aquaglyceroporins are important for the release of ammonia derived from amino acid breakdown.
Authors:
Thomas Zeuthen; Binghua Wu; Slavica Pavlovic-Djuranovic; Lars M Holm; Nestor L Uzcategui; Michael Duszenko; Jürgen F J Kun; Joachim E Schultz; Eric Beitz
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2006-08-03
Journal Detail:
Title:  Molecular microbiology     Volume:  61     ISSN:  0950-382X     ISO Abbreviation:  Mol. Microbiol.     Publication Date:  2006 Sep 
Date Detail:
Created Date:  2006-09-13     Completed Date:  2006-11-28     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8712028     Medline TA:  Mol Microbiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  1598-608     Citation Subset:  IM    
Affiliation:
Nordic Centre for Water Imbalance Related Disorders, Department of Medical Physiology, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen N, Denmark.
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MeSH Terms
Descriptor/Qualifier:
Ammonia / metabolism*
Animals
Aquaglyceroporins / genetics,  physiology*
Genetic Complementation Test
Membrane Proteins / genetics,  physiology
Methylamines / toxicity
Oocytes
Permeability
Plasmodium falciparum / growth & development*,  metabolism
Saccharomyces cerevisiae / genetics,  physiology
Saccharomyces cerevisiae Proteins / genetics,  physiology
Toxoplasma / growth & development*,  metabolism
Trypanosoma brucei brucei / growth & development*,  metabolism
Xenopus laevis
Chemical
Reg. No./Substance:
0/Aquaglyceroporins; 0/FPS1 protein, S cerevisiae; 0/Membrane Proteins; 0/Methylamines; 0/Saccharomyces cerevisiae Proteins; 74-89-5/methylamine; 7664-41-7/Ammonia

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