title: The kinetics of the active and de-energized transport of O-methyl glucose in Ustilago maydis.
abstract: The kinetics of the uptake and efflux of 3-O-methyl-glucose in sporidia of Ustilago maydis were measured, both in active cells and in cells whose metabolic activity had been inhibited by azide and iodoacetate. The de-energized transport system proved to be carrier mediated with apparent affinity constants 13 +/- 2 mM outside (Ko) and 18 +/- 2 mM inside (K1). The apparent maximum rate constants for the same system were 0.66 +/- 0.05 mmol/1 cell water per min for uptake (V+) and 0.53 +/- 0.04 mmol/l cell water per min for efflux (V-). For the active system K0 = 0.08 +/- 0.01, K1 greater than 40, V+ = 9.7 +/- 0.5 and V- = 1.1 +/- 0.9 (in equivalent units). These results are discussed in the context of the carrier mechanism as proposed by Regen and Morgan (Regen, D.M. and Morgan, H.E. (1964) Biochim. Biophys. Acta 79, 151--166). The antifungal compound carboxin had no effect on de-energized transport but was shown to decrease both K0 And V+ in the active system. Phloretin and phlorizin were also found to be without effect on de-energized cells but the former enhanced while the latter inhibited active uptake.
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D001386:Azides / Q000494:pharmacology; D001487:Basidiomycota / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002261:Carboxin / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007461:Iodoacetates / Q000494:pharmacology; D007700:Kinetics; D008757:Methylglucosides / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D010695:Phlorhizin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D014588:Ustilago / Q000378:metabolism*
chemical_list: D001386:Azides; D007461:Iodoacetates; D008757:Methylglucosides; D008759:Methylglycosides; D002261:Carboxin; D000968:Antimycin A; D012964:Sodium; D010695:Phlorhizin; D011188:Potassium