RESUMEN
Allosteric regulation has traditionally been described by mathematically-complex allosteric rate laws in the form of ratios of polynomials derived from the application of simplifying kinetic assumptions. Alternatively, an approach that explicitly describes all known ligand-binding events requires no simplifying assumptions while allowing for the computation of enzymatic states. Here, we employ such a modeling approach to examine the "catalytic potential" of an enzyme-an enzyme's capacity to catalyze a biochemical reaction. The catalytic potential is the fundamental result of multiple ligand-binding events that represents a "tug of war" among the various regulators and substrates within the network. This formalism allows for the assessment of interacting allosteric enzymes and development of a network-level understanding of regulation. We first define the catalytic potential and use it to characterize the response of three key kinases (hexokinase, phosphofructokinase, and pyruvate kinase) in human red blood cell glycolysis to perturbations in ATP utilization. Next, we examine the sensitivity of the catalytic potential by using existing personalized models, finding that the catalytic potential allows for the identification of subtle but important differences in how individuals respond to such perturbations. Finally, we explore how the catalytic potential can help to elucidate how enzymes work in tandem to maintain a homeostatic state. Taken together, this work provides an interpretation and visualization of the dynamic interactions and network-level effects of interacting allosteric enzymes.
Asunto(s)
Regulación Alostérica/fisiología , Glucólisis/fisiología , Unión Proteica/fisiología , Fenómenos Biofísicos/fisiología , Catálisis , Simulación por Computador , Hexoquinasa/metabolismo , Hexoquinasa/farmacocinética , Humanos , Cinética , Ligandos , Fosfofructoquinasa-1/metabolismo , Fosfofructoquinasa-1/farmacocinética , Piruvato Quinasa/metabolismo , Piruvato Quinasa/farmacocinética , TermodinámicaRESUMEN
Specimens of Trematomus bernacchii were caught by hooks near the Japanese Antarctic Station of Syowa during the month of January, 1992. The caught animals were taken to the Laboratory at the Icebreaker Shirase. Epaxial and cardiac muscles were dissected, washed thoroughly with chilled saline and used for the preparation of phosphofructokinase (PFK) and hexokinase (HK). Liver, encephalon, and whole blood were also obtained and used for the preparation of crude extracts and hemolysates. The following kinetic data were obtained for PFK: the apparent Km for F-6-P in the presence of 216MuM of ATP; the apparent Km for ATP in the presence 1mM of F-6-P. In both cases, the experiments were carried out at 20 degrees Celsius, pH 8.0. At this pH, the fish PFK did not display allosteric properties. The allosteric behavior of this preparation of PFK was assayed at pH 7.0. Levels of HK assayed in tissues crude extracts and red blood cells hemolysates gave the following results in specific activity (mU/mg protein): cardiac muscle, 62; encephalon, 18; liver, 2.7; RBC hemolysates, 0.0; epaxial muscle, 0.0. The ATP and glucose apparent Km were assayed for the cardiac muscle HK.