Examination of the mechanism of Na+/phosphate cotransport. Use of fluorophosphate and the nature of cotransporter functional asymmetry.
The effect of substrates and mono- and di-fluorophosphates on Na+/phosphate cotransport by intestinal SDS-BBM vesicles was examined. Internal Na+ inhibited Na+/phosphate cotransport and this inhibition was relieved by internal phosphate. Inhibition by internal Na+ displayed Michaelis-Menten kinetics in contrast to the sigmoidal behavior for Na+ activation of phosphate uptake. Difluorophosphate but not monofluorophosphate inhibited Na+/phosphate cotransport in the external medium. In contrast, in the absence of internal Na+ monofluorophosphate but not difluorophosphate inhibited phosphate uptake. These results suggest that the intestinal Na+/phosphate cotransporter is functionally asymmetric in its substrate specificity.
Peerce
B E
BE
Department of Physiology and Biophysics, UTMB, Galveston.
Kiesling
C
C
D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D005459:Fluorides / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000648:ultrastructure; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism* / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters
D002352:Carrier Proteins; D010710:Phosphates; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; C012980:fluorophosphate; D012964:Sodium; D005459:Fluorides