Abstract
Catabolite inactivation of the galactose uptake system in yeast.
Highlights
From the Biochemisches Institut der Uniuersitiit Freiburg im Breisgau der Gesellschaft fiir Strahlen- und Umweltforschung, D-78 Freiburg and Abteilung im Breisgau, fiir Enzymchemie Germany
After addition of glucose to galactose-grown cells of Saccharomyces cereuisiae the activities of the following enzymes of galactose utilization were assayed: the galactose uptake system, galactokinase, galact,ose-l-phosphate uridyltransferase, UDP-galactose-4-epimerase, and phosphoglucomutase
From these findings and from the observation that the galactose uptake system exhibits the lowest specific activity of the five enzymes which channel galactose into the glucose degradation pathway, it is concluded that a decrease in the affinity for galactose of the galactose uptake system is responsible for the catabolite inactivation of the galactose-fermenting system in S. cereuisiae
Summary
From the Biochemisches Institut der Uniuersitiit Freiburg im Breisgau der Gesellschaft fiir Strahlen- und Umweltforschung, D-78 Freiburg and Abteilung im Breisgau, fiir Enzymchemie Germany. In contrast to the observation on the galactose uptake system, no significant changes were observed in the activities of the enzymes of the pathway from intracellular galactose to glucose &phosphate (galactokinase, galactose-l-phosphate uridyltransferase, UDP-galactose-4-epimerase, and phosphoglucomutase) after addition of glucose to galactose-grown cells From these findings and from the observation that the galactose uptake system exhibits the lowest specific activity of the five enzymes which channel galactose into the glucose degradation pathway, it is concluded that a decrease in the affinity for galactose of the galactose uptake system is responsible for the catabolite inactivation of the galactose-fermenting system (galactozymase) in S. cereuisiae. This catabolite inactivation of galactozymase activity does not disturb the ability of the cells to ferment glucose (3) It appears that the enzyme(s) inactivated should be part of the pathway of conversion of galactose in the medium to intracellular glucose 6-phosphate, which is catalyzed sequentially by the galactose uptake system, galactokinase, galactose-l-phosphate uridyltransferase, UDP-galactose-4-epimerase, and phosphoglucomutase. In the present paper it is shown that of these it is the galactose uptake system which is subject to catabolite inactivation
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