Reciprocal influence of glucose anomers upon their respective phosphorylation by hexokinase.
The phosphorylation of D-glucose (1.0mM) was measured in homogenates of tumoral islet cells incubated at 7 degrees C in the presence of labelled alpha- and/or beta-D-glucose, with or without exogenous glucose 6-phosphate. The close-to-maximal reaction velocity of hexokinase was higher with beta- than alpha-D-glucose. The latter anomer inhibited beta-D-glucose phosphorylation more than the beta-anomer decreased the phosphorylation of alpha-D-glucose. This behaviour was accounted for by the higher affinity of hexokinase for alpha- than for beta-D-glucose. These direct measurements of the relative contribution of each anomer to the overall rate of glucose phosphorylation in the presence of mixed populations of alpha- and beta-D-glucose validate the concept that the phosphorylation of D-glucose displays anomeric specificity even when the hexose is used at anomeric equilibrium. Glucose 6-phosphate inhibited the phosphorylation of the two anomers more severely when alpha-D-glucose rather than beta-D-glucose was the most abundant anomer.
D000818:Animals; D002250:Carbon Radioisotopes; D002460:Cell Line; D005947:Glucose / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism*; D007340:Insulinoma / Q000378:metabolism; D007700:Kinetics; D010190:Pancreatic Neoplasms / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D013237:Stereoisomerism; D014316:Tritium
D002250:Carbon Radioisotopes; D014316:Tritium; D006593:Hexokinase; D005947:Glucose