Dissimilar effects of D-mannoheptulose on the phosphorylation of alpha- versus beta-D-glucose by either hexokinase or glucokinase.
D-mannoheptulose inhibits D-glucose phosphorylation by hexokinase isoenzymes. The present study aims at investigating whether the pattern of such an inhibition differs in the case of alpha- versus beta-D-glucose. The phosphorylation of alpha- and beta-D-[U-14C]glucose was measured over 60-min incubation at 4 degrees C in the presence of bovine heart hexokinase and over 10 min at 24 degrees C in the presence of human liver glucokinase. The relative extent of the inhibitory action of D-mannoheptulose (0.02-10.0 mM) was always less marked with alpha- than beta-D-glucose. In the case of hexokinase, the experiments conducted at the high concentration of the D-glucose anomers (1.0 mM) revealed that D-mannoheptulose, at low concentrations (0.2-0.5 mM), may unexpectedly increase the phosphorylation of alpha-D-glucose. These findings thus document anomeric specificity in terms of the inhibitory action of D-mannoheptulose upon alpha- versus beta-D-glucose phosphorylation by either hexokinase or glucokinase.
Zhang
Ying
Y
Laboratory of Experimental Hormonology, Brussels Free University, 808 Route de Lennik, B-1070 Brussels, Belgium.
Courtois
Philippe
P
Sener
Abdullah
A
Malaisse
Willy J
WJ
D000818:Animals; D002417:Cattle; D005941:Glucokinase / Q000037:antagonists & inhibitors*; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D006593:Hexokinase / Q000037:antagonists & inhibitors*; D006801:Humans; D007700:Kinetics; D008356:Mannoheptulose / Q000737:chemistry / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects
D008356:Mannoheptulose; D006593:Hexokinase; D005941:Glucokinase; D005947:Glucose