SYSTEMS-ANALYSIS OF YEAST GYLCOLYSIS USING PERTURBATIONS OF EXTERNAL PH - PHYSIOLOGICAL-PARAMETERS, NONPARAMETRIC ANALYSIS, AND GENERAL-PROPERTIES OF THE SYSTEM DYNAMICS

A global systems analysis approach to yeast glycolysis is presented. S tarting from a high flux steady state of anaerobic glycolysis rapid ch anges of external pH are applied. The dynamics of the transduction of the pH signal to the in vivo fluorescence of reduced pyridine nucleoti des are investigated. Physiological studies indicate no significant in fluence of external pH on glycolytic flux and energy charge, but stati onary concentrations of metabolites are increased after increasing the external pH from 5-7 particularly in the distal part of the glycolyti c 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 r espect to the input amplitude. The dynamic properties of the system de pend on the state of adaptation to a certain external pH. The non-para metric model derived from single step experiments was used to correctl y predict the response to pulses of variable duration. This indicates that the linear macroscopic approach to systems analysis with pH as in put is applicable. The dynamics of the system response includes strong ly 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.