The hypoxanthine transporter of Novikoff rat hepatoma cells exhibits directional symmetry and equal mobility when empty or substrate-loaded.
The kinetics of hypoxanthine transport were measured in hypoxanthine phosphoribosyltransferase-deficient Novikoff cells by rapid kinetic techniques applying both zero-trans and equilibrium exchange protocols. The data indicate operation of a simple carrier with directional symmetry and equal mobility when substrate loaded and empty. Zero-trans influx and efflux were about equivalent and so were zero-trans influx and equilibrium exchange flux. The apparent Michaelis-Menten constant and maximum velocity were about 500 microM and 100 pmol/s per microliter cell H2O, respectively. The time courses of accumulation of radioactively labeled hypoxanthine at a concentration above the Michaelis-Menten constant differed noticeably in zero-trans and equilibrium exchange mode, but computer simulations showed that the difference is predicted by the symmetrical carrier model and does not reflect trans-stimulation.
D000818:Animals; D001693:Biological Transport, Active; D007041:Hypoxanthine Phosphoribosyltransferase / Q000172:deficiency; D007042:Hypoxanthines / Q000378:metabolism*; D007700:Kinetics; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D051381:Rats
D007042:Hypoxanthines; D007041:Hypoxanthine Phosphoribosyltransferase