DISTRIBUTED CONTROL OF THE GLYCOLYTIC FLUX IN WILD-TYPE CELLS AND CATABOLITE REPRESSION MUTANTS OF SACCHAROMYCES-CEREVISIAE GROWING IN CARBON-LIMITED CHEMOSTAT CULTURES

The sensitivity of the control of glycolysis was studied in the wild-t ype (WT) strain CEN.PK122 and in isogenic catabolite-repression mutant s growing in carbon-limited, aerobic chemostat cultures at different d ilution rates, D. Based on a model of glycolysis in which the glucose transport step was considered reversible and inhibited by glucose 6-ph osphate (G6P), the matrix method of metabolic control analysis was app lied. In the present work, we report that the control of glycolysis wa s significantly distributed between the glucose uptake, hexokinase, an d phosphofructokinase steps. The flux control properties were sensitiv e to the glucose gradient through the membrane and the extent of inhib ition of the transport by G6P as parameters of the glucose-uptake kine tics in all strains tested. In the WT strain at low and high D, most o f the control was exerted by the phosphofructokinase (PFK)-catalyzed s tep. In the cat1 mutant, the step catalyzed by PFK was the most rate c ontrolling while in the cat3 strain, the control was shared between th e PFK, hexokinase (HK), and glucose transport steps. On the other hand , the mig1 mutant exhibited high control by the glucose transporter de pending on the glucose gradient across the membrane. The results obtai ned are discussed in terms of the dependence upon the type of metaboli sm displayed by yeast and the kinetics of the sugar transport step. (C ) 1997 Elsevier Science Inc.