Slow ligand-induced transitions in the allosteric phosphofructokinase from Escherichia coli

摘要: The fluorescence of the unique tryptophan residue allosteric phosphofructokinase from Escherichia coli varies upon binding any ligand, whether substrate or effector, suggesting that protein undergoes a conformational change. This fluorescent probe has been exploited to determine rates structural transitions occur ligand and are responsible for remarkable behavior this enzyme. kinetics changes measured after rapidly mixing with one its ligands show presence several widely different rates, ranging few hundred s−1 less than 0.1 s−1. rate each change increases concentration used trigger it, induce do not displace pre-existing equilibrium. hypothesis stabilizes state is confirmed by displacement another: instance, binary complexes between either substrate, fructose-6-phosphate, activator, ADP, have same low should be in active state, but they transition inhibitor phosphoenolpyruvate. It appears can exist more two states. Some these multiple states slow enough play an important role reaction catalyzed phosphofructokinase, could even explain part behavior. These results steady-state measurements sufficient analyze regulatory properties E. phosphofructokinase.