Mannose enters mammalian cells using a specific transporter that is insensitive to glucose.
The concentration of D-mannose in serum is 20-50 micron, but its physiological significance for glycoprotein synthesis is unknown. Here, we show that the uptake of D-mannose by different mammalian cell lines involves a mannose-specific transporter(s) with a K(uptake) of about 30-70 micron and a V(max) which is probably sufficient to account for the bulk of mannose needed for glycoprotein synthesis. Mannose uptake appears to be through a facilitated transport process since it is not inhibited by cyanide. Phloretin completely inhibits mannose uptake, but phloridzin inhibits only 25-30%. Both of these inhibitors can block 2-deoxyglucose uptake in fibroblasts which occurs through the typical glucose transporters. None of 9 other sugars tested inhibited mannose transport. Most importantly, 5 mM D-glucose only inhibits mannose uptake by 50% showing that it is not an efficient competitor. These results suggest that this transporter(s) may use serum mannose for glycoprotein synthesis.
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La Jolla Cancer Research Foundation, La Jolla, California 92037, USA.
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D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D003847:Deoxyglucose / Q000378:metabolism; D004285:Dogs; D005347:Fibroblasts; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007668:Kidney; D007700:Kinetics; D008264:Macrophages; D008322:Mammals; D008358:Mannose / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000037:antagonists & inhibitors; D009005:Monosaccharides / Q000494:pharmacology; D009457:Neuroglia; D010693:Phloretin / Q000494:pharmacology; D051381:Rats; D012867:Skin
D002352:Carrier Proteins; D009004:Monosaccharide Transport Proteins; D009005:Monosaccharides; D003847:Deoxyglucose; D005947:Glucose; D008358:Mannose; D010693:Phloretin