title: Kinetics of the activation of rat liver pyruvate kinase by fructose 1,6-diphosphate and methods for characterizing hysteretic transitions.
abstract: 1. Kinetics of fructose 1,6-diphosphate activation of liver pyruvate kinase type I inhibited with MgATP and l-alanine are described as a function of enzyme and fructose 1,6-diphosphate concentrations. These results can be explained by a single pseudo-first-order transition of the enzyme into an active form, independent of the enzyme concentration. This rate constant, k(app.)=0.24s(-1) with 0.02mm-fructose 1,6-diphosphate (t(0.9) approximately 10s where t(0.9) is the time for 90% conversion), is an increasing function of fructose 1,6-diphosphate concentration far beyond that needed to maximally activate enzyme equilibrated with fructose 1,6-diphosphate (about 20mum). 2. The model equations are best analysed with numerical techniques which are described. These techniques are useful in studying similar slow transients frequently observed in stopped-flow studies of enzymes. 3. Shorter transients (t(0.9)=0.5-1.5s) were observed in the kinetic response of the enzyme to the addition of MgATP or phosphoenolpyruvate, but were not further characterized.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000409:Alanine / Q000494:pharmacology; D000818:Animals; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004789:Enzyme Activation; D005636:Fructosephosphates / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008274:Magnesium / Q000494:pharmacology; D008954:Models, Biological; D010728:Phosphoenolpyruvate / Q000378:metabolism; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats
chemical_list: D005636:Fructosephosphates; D010728:Phosphoenolpyruvate; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase; D008274:Magnesium; D000409:Alanine