Steady-state kinetics of catecholamine transport by chromaffin-granule "ghosts".
Resealed chromaffin-granule ;ghosts' were used to study the steady-state kinetics of catecholamine transport. The pump has a high affinity for (-)-noradrenaline, (-)-adrenaline, tyramine and 5-hydroxytryptamine (serotonin), but a lower affinity for (+)-noradrenaline. The measured rates of incorporation do not conform to Michaelis-Menten kinetics, but affinity constants for the former substrates are in the range 8-18mum. Reserpine is a potent inhibitor. Incorporation as a function of ATP concentration also fails to show simple kinetics; the affinity constant for ATP is deduced to be about 3mm at 1mm-MgCl(2). Adenylyl (betagamma-methylene)diphosphonate is a competitive inhibitor at low concentrations, but inhibits more strongly at high concentrations. The pump has a transition temperature at 29 degrees C and does not seem to be identical with the Mg(2+)-stimulated adenosine triphosphatase of chromaffin granules.
D000255:Adenosine Triphosphate / Q000378:metabolism; D001667:Binding, Competitive; D001693:Biological Transport, Active; D002395:Catecholamines / Q000378:metabolism*; D002712:Chlorides; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism*; D004837:Epinephrine / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium; D009638:Norepinephrine / Q000378:metabolism; D012110:Reserpine / Q000494:pharmacology; D012701:Serotonin / Q000378:metabolism; D013696:Temperature; D014439:Tyramine / Q000378:metabolism
D002395:Catecholamines; D002712:Chlorides; D012701:Serotonin; D012110:Reserpine; D000255:Adenosine Triphosphate; D008274:Magnesium; D009638:Norepinephrine; D014439:Tyramine; D004837:Epinephrine