D-mannoheptulose phosphorylation by hexokinase isoenzymes.
D-mannoheptulose is a specific inhibitor of D-glucose phosphorylation by hexokinase isoenzymes. In the present study, the phosphorylation of this heptose was investigated by either a spectrophotometric or radioisotopic procedure. Using yeast hexokinase, the phosphorylation of 25 mM D-mannoheptulose only represented 0.02% of that of 5 mM D-glucose. Such a percentage was increased to 3.93% in the case of bovine heart hexokinase. In the latter case, the Km for D-mannoheptulose was close to 0.2 mM and both D-glucose (0.1-1.0 mM) and D-glucose 6-phosphate (also 0.1-1.0 mM) inhibited the phosphorylation of the heptose (0.03-0.60 mM). Human B-cell glucokinase also catalyzed the phosphorylation of D-mannoheptulose (0.1 mM), which was now increased in a bell-shaped manner by D-glucose (1.0-20 mM). Likewise, rat parotid gland, liver and pancreatic islet homogenates catalyzed the phosphorylation of D-[3H]mannoheptulose. The results obtained in these three tissues differed from one another by their absolute values (per mg wet wt.), relative values (by reference to the phosphorylation rate of 10 mM D-glucose), and sensitivity to inhibition by D-glucose (10 mM).
Laboratory of Experimental Medicine, Brussels Free University, Brussels, Belgium.
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P
Courtois
A
A
Sener
W J
WJ
Malaisse
D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology; D002417:Cattle; D005941:Glucokinase / Q000235:genetics / Q000378:metabolism; D006593:Hexokinase / Q000378:metabolism*; D006801:Humans; D007515:Islets of Langerhans / Q000201:enzymology; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D008297:Male; D008356:Mannoheptulose / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology; D009928:Organ Specificity; D010306:Parotid Gland / Q000201:enzymology; D010766:Phosphorylation; D051381:Rats
D007527:Isoenzymes; D008356:Mannoheptulose; D006593:Hexokinase; D005941:Glucokinase