title: Monosaccharide transport into hemocytes of a sipunculan worm Themiste dyscrita.
abstract: The hemerythrin-containing blood cells, or hemocytes, of the sipunculan worm Themiste dyscrita were found to have a stereospecific and nonconcentrative monosaccharide transport system. The transport system transferred both D-glucose and 3-O-methyl-D-glucose (3-OMG), and transport into cells by this system was rapid, reaching 50% equilibrium in approximately 20 s at 10 degrees C with an initial concentration gradient of 0.1 mM; the contribution to total uptake by simple diffusion was very small. 3-OMG uptake showed saturation kinetics with a low half-saturation constant (Km less than or equal to 0.1 mM). The uptake of labeled 3-OMG by the hemocytes was strongly inhibited by unlabeled 3-OMG, 2-deoxy-D-glucose, alpha- and beta-D-glucose, D-galactose, and D-mannose. It was moderately inhibited by D-xylose, only slightly by alpha-methyl-D-glucoside and D-fructose, and uninhibited by sucrose, L-glucose, or D-sorbitol. Phloretin was more potent than phloridzin in blocking entry of 3-OMG. Cytochalasin B did not bind tightly to the T. dyscrita transporter and was not a potent inhibitor of transport; it half-maximally inhibited 3-OMG transport at 0.1 mM. Therefore, despite some differences the data suggest functional similarities in the mechanism of monosaccharide transport into blood cells of mammals and this invertebrate.
mesh_terms: D019325:3-O-Methylglucose; D000818:Animals; D001692:Biological Transport; D001773:Blood Cells / Q000378:metabolism*; D006434:Hemocytes / Q000378:metabolism*; D007700:Kinetics; D008757:Methylglucosides / Q000378:metabolism; D009005:Monosaccharides / Q000378:metabolism*; D009348:Nematoda / Q000378:metabolism*; D013997:Time Factors; D014316:Tritium
chemical_list: D008757:Methylglucosides; D009005:Monosaccharides; D014316:Tritium; D019325:3-O-Methylglucose