Can yeast glycolysis be understood in terms of in vitro kinetics of the constituent enzymes? Testing biochemistry

This paper examines whether the in vivo behavior of yeast glycolysis can be understood in terms of the in vitro kinetic properties of the constituent enzymes. In nongrowing, anaerobic, compressed Saccharomyces cerevisiae the values of the kinetic parameters of most glycolytic enzymes were determined . For the other enzymes appropriate literature values were collected. By in serting these values into a kinetic model for glycolysis, fluxes and metabo lites were calculated. Under the same conditions fluxes and metabolite leve ls were measured. In our first model, branch reactions were ignored. This model failed to rea ch the stable steady state that was observed in the experimental flux measu rements. Introduction of branches towards trehalose, glycogen, glycerol and succinate did allow such a steady state. The predictions of this branched model were compared with the empirical behavior. Half of the enzymes matche d their predicted flux in vivo within a factor of 2. For the other enzymes it was calculated what deviation between in vivo and in vitro kinetic chara cteristics could explain the discrepancy between in vitro rate and in vivo flux.