title: Kinetic characteristics of the two glucose transport systems in Neurospora crassa.
abstract: Glucose is transported across the cell membrane of Neurospora crassa by two physiologically and kinetically distinct transport systems. System II is repressed by growth of the cells in 0.1 m glucose. System I is synthesized constitutively. The apparent K(m) for glucose uptake by system I and system II are 25 and 0.04 mm, respectively. Both uptake systems are temperature dependent, and are inhibited by NaN(3) and 2,4-dinitrophenol. Glucose uptake by system II was not inhibited by fructose, galactose, or lactose. However, glucose was shown to be a noncompetitive inhibitor of fructose and galactose uptake. The transport rate of [(14)C]3-0-methyl-d-glucose (3-0-MG) was higher in cells preloaded with unlabeled 3-0-MG than in control cells. The rate of entry of labeled 3-0-MG was only slightly inhibited by the presence of NaN(3) in the medium. Further, NaN(3) caused a rapid efflux of accumulated [(14)C]3-0-MG. These data imply that the energetic step in the transport process prevents efflux.
mesh_terms: D001345:Autoradiography; D001692:Biological Transport; D001693:Biological Transport, Active; D002247:Carbon Isotopes; D002854:Chromatography, Paper; D003470:Culture Media; D004058:Diffusion; D004140:Dinitrophenols / Q000494:pharmacology; D005374:Filtration; D005632:Fructose / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D005990:Glycerol / Q000378:metabolism; D007785:Lactose / Q000378:metabolism; D009491:Neurospora / Q000254:growth & development / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D003470:Culture Media; D004140:Dinitrophenols; D005632:Fructose; D005947:Glucose; D007785:Lactose; D005990:Glycerol; D005690:Galactose