Potassium transport in Neurospora. Evidence for a multisite carrier at high pH.
At low extracellular pH (4-6), net uptake of potassium by Neurospora is a simple exponential process which obeys Michaelis kinetics as a function of [K](o). At high pH, however, potassium uptake becomes considerably more complex, and can be resolved into two distinct exponential components. The fast component (time constant = 1.2 min) is matched quantitatively by a rapid loss of sodium; it is attributed to ion exchange within the cell wall, since it is comparatively insensitive to low temperature and metabolic inhibitors. By contrast, the slower component (time constant = 10.9 min) is inhibited markedly at 0 degrees C and by CN and deoxycorticosterone, and is thought to represent carrier-mediated transport of potassium across the cell membrane. This transport process exhibits sigmoid kinetics as a function of [K](o); the data can be fitted satisfactorily by two different two-site models (one involving a carrier site and a modifier site, the other an allosteric model). Either of these models could also accommodate the simple Michaelis kinetics at low pH.
D001693:Biological Transport, Active; D003486:Cyanides / Q000494:pharmacology; D003864:Depression, Chemical; D003900:Desoxycorticosterone / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D007700:Kinetics; D008954:Models, Biological; D009491:Neurospora / Q000187:drug effects / Q000378:metabolism*; D010101:Oxygen Consumption; D011188:Potassium / Q000378:metabolism*
D003486:Cyanides; D003900:Desoxycorticosterone; D011188:Potassium