Systems analysis of yeast glycolysis using perturbations of external pH: physiological parameters, non-parametric...

A global systems analysis approach to yeast glycolysis is presented. Starting from a high flux steady state of anaerobic glycolysis rapid changes of external pH are applied. The dynamics of the transduction of the pH signal to the in vivo fluorescence of reduced pyridine nucleotides are investigated. Physiological studies indicate no significant influence of external pH on glycolytic flux and energy charge, but stationary concentrations of metabolites are increased after increasing the external pH from 5-7 particularly in the distal part of the glycolytic chain. Most of the changes in reduced pyridine fluorescence are due to glycolytically accessible NADH. As a first stage of system analytic investigations the premises for the approach were tested. The dynamic properties of the system are stable and the response is linear with respect to the input amplitude. The dynamic properties of the system depend on the state of adaptation to a certain external pH. The non-parametric model derived from single step experiments was used to correctly predict the response to pulses of variable duration. This indicates that the linear macroscopic approach to systems analysis with pH as input is applicable. The dynamics of the system response includes strongly damped oscillatory components. Their period lengths are similar to those found with temperature inputs and with the switching from low to high glycolytic flux under anaerobic conditions. This indicates that the three different signals may trigger common regulatory interactions. The order of the signal transduction process, indicating the number of basic processes involved, can be estimated to be 4 or higher.