Chromatographic resolution and kinetic characterization of glucokinase from islets of Langerhans.
Glucokinase (ATP:D-glucose 6-phosphotransferase, EC 2.7.1.2) from rat islets of Langerhans was partially purified by chromatography on DEAE-Cibacron blue F3GA agarose. The enzyme eluted in two separate peaks. Sigmoidal rate dependence was found with respect to glucose (Hill coefficient = 1.5) for both enzyme fractions. Km values for glucose were 5.7 mM for the major fraction and 4.5 mM for the minor fraction. Neither fraction phosphorylated GlcNAc. A GlcNAc kinase (ATP:2-acetamido-2-deoxy-D-glucose 6-phosphotransferase, EC 2.7.1.59)-enriched fraction, prepared by affinity chromatography on Sepharose-N-(6-aminohexanoyl)-GlcNAc, had a Km of 25 microM for GlcNAc. Islet tissue also contained hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) eluting in multiple peaks. The results are consistent with the concept that glucokinase serves as the glucose sensor of pancreatic beta cells.
D000818:Animals; D001921:Brain / Q000201:enzymology; D002845:Chromatography; D005941:Glucokinase / Q000302:isolation & purification / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism; D007515:Islets of Langerhans / Q000201:enzymology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008297:Male; D051381:Rats
D006593:Hexokinase; D005941:Glucokinase