[Mathematical modelling of glycolysis and of adenine nucleotide metabolism of human erythrocytes. II. Simulation of adenine nucleotide breakdown following glucose depletion].

The breakdown of adenine nucleotides in human erythrocytes in physiological and alkaline medium at 37 degrees C after glucose depletion is simulated by a mathematical model of energy metabolism. The simulation consists of time dependent solutions of a system of 16 differential equations derived from the stoichiometry of chemical pathways and kinetic properties of enzymes. Starting with the stationary characteristics of the model (M. Schauer et al.: Acta biol. med. germ. 40, 1659, 1981) the results of the simulation were analysed as a function of 1) the share of adenylate deaminase in the degradation of adenine nucleotides and 2) the interaction between adenylate kinase equilibrium and magnesium ions. The experimental data and the simulated concentration changes are in good accord, provided that the assumed activity of adenylate deaminase is very low so that the degradation of adenine nucleotides proceeds mainly via AMP-hydrolysis. The extensive activation of adenylate deaminase during incubation is explained by its sigmoid kinetics with respect to AMP. To improve the results of simulation changes in the adenylate kinase equilibrium have to taken into consideration. These have been measured during incubation of erythrocytes; they can be attributed only partly to the increasing concentration of magnesium ions and to differences among the constants of magnesium association to adenine nucleotides.