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Am J Physiol Regul Integr Comp Physiol 296: R1268-R1273, 2009. First published January 14, 2009; doi:10.1152/ajpregu.90726.2008
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WATER AND ELECTROLYTE HOMEOSTASIS

Functional characterization of Actinobacillus pleuropneumoniae urea transport protein, ApUT

Geeta Godara,1 Craig Smith,3 Janine Bosse,4 Mark Zeidel,2 and John Mathai2

1Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania; 2Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts; 3Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom; 4Molecular Infectious Disease Group, Department of Paediatrics, Imperial College London, St. Mary's Campus, London, United Kingdom

Submitted 26 August 2008 ; accepted in final form 8 January 2009

Urea transporters (UTs) effect rapid flux of urea across biological membranes. In the mammalian kidney, UT activity is essential for effective urine concentration. In bacteria, UT-mediated urea uptake permits intracellular urease to degrade urea to ammonia and CO2, a process that either buffers acid loads or provides nutrient nitrogen. We have characterized the urea transport channel protein ApUT from Actinobacillus pleuropneumoniae. Kinetic analysis of bacterial inside-out membranes enriched in ApUT showed ~28-fold increase in urea permeability (3.3 ± 0.4 x 10–4 cm/s) compared with control vesicles (0.11 ± 0.02 x 10–4 cm/s). In addition to urea, ApUT also conducts water. Urea and water transport across the channel was phloretin and mercury inhibitable, and the site of inhibition may be located on the cytoplasmic side of the protein. Glycerol and urea analogs, such as methylamine, dimethylurea, formamide, acetamide, methylurea, propanamide, and ethylamine did not permeate across ApUT.

urea permeability; water permeability; bacterial vesicles; urea analogs


Address for reprint requests and other correspondence: J. Mathai, Beth Israel Deaconess Medical Center, 840 Memorial Dr., Cambridge, MA 02139 (e-mail: jmathai{at}bidmc.harvard.edu)






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