LACK OF LACTATE-PROTON SYMPORT ACTIVITY IN PCK1 MUTANTS OF SACCHAROMYCES-CEREVISIAE

Mutants of Saccharomyces cerevisiae without phosphoenolpyruvate carbox ykinase activity showed no measurable lactate proton symport, while mu tants without fructose-1,6-bisphosphatase had normal transport activit y. Incubation of a pck1 mutant, under derepression conditions in the p resence of glycerol, restored the activity of the lactate-proton sympo rt, with identical kinetic characteristics to that in the wild-type. F or efficient lactate-proton symport activity, not only is an external inducer such as lactic acid needed, but also a molecule derived from t he acid metabolism may be necessary.