Inhibition and inactivation of glucose-phosphorylating enzymes from Saccharomyces cerevisiae by D-xylose.
Three glucose-phosphorylating enzymes were separated from cell-free extracts of Saccharomyces cerevisiae by hydroxylapatite chromatography. Variations in the amounts of these enzymes in cells growing on glucose and on ethanol showed that hexokinase PI was a constitutive enzyme, whereas synthesis of hexokinase PII and glucokinase were regulated by the carbon source used. Glucokinase proved to be a glucomannokinase with Km values of 0.04 mM for both glucose and mannose. D-Xylose produced an irreversible inactivation of the three glucose-phosphorylating enzymes depending on the presence or absence of ATP. Hexokinase PI inactivation required ATP, while hexokinase PII was inactivated by D-xylose without ATP in the reaction mixture. Glucokinase was protected by ATP from this inactivation. D-Xylose acted as a competitive inhibitor of hexokinase PI and glucokinase and as a non-competitive inhibitor of hexokinase PII.
D003513:Cycloheximide / Q000494:pharmacology; D005941:Glucokinase / Q000037:antagonists & inhibitors*; D005947:Glucose / Q000378:metabolism; D006593:Hexokinase / Q000037:antagonists & inhibitors*; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D014994:Xylose / Q000494:pharmacology*
D007527:Isoenzymes; D003513:Cycloheximide; D014994:Xylose; D006593:Hexokinase; D005941:Glucokinase; D005947:Glucose