Further properties and possible mechanism of action of adenosine 5′-triphosphate–d-glucose 6-phosphotransferase from rat liver

Abstract

1. Magnesium ions are the most effective bivalent ions in the glucokinase reaction. 2. The molecular weight of rat hepatic glucokinase is 48000-49000 as assessed by gel filtration on Sephadex G-100. 3. Anomalous kinetic behaviour at low glucose concentrations appears to be due to the formation during the purification procedure of fragments possessing modified catalytic properties, but is unlikely to be of physiological significance. 4. Extension of previous studies (Parry & Walker, 1966) suggests that glucokinase catalyses a reaction of the random Bi Bi type similar to that of yeast hexokinase. 5. The inhibitory effects of various thiol reagents suggest that a thiol group may be involved at or near the binding site of the acceptor molecule.

Comments on the Kinetics and Mechanism of Yeast Hexokinase Action

“…Other details are presented in the legend to Fig. 3 for glucokinase which is also believed to involve random substrate binding [25].…”

Isolation and characterization of a thermophilic glucokinase fromBacillus stearothermophilus

“…Whereas the hexokinases isolated from, e.g. mammalian brain [1], and yeast [2,3] are unspecific (by definition) and achieve phosphorylation of D-glucose, D-fructose, D-mannose, 2-deoxy-D-glucose and other substrates, very specific glucokinases isolated from liver [4], Aerobacter aerogenes [5] and Entamoeba histolytica [6] have been described. N-Acetyl-Dglucosamine kinases from Streptomyces pyrogenes [7] and E. coli [8] seem to be related to hexokinase and glucokinase respectively.…”

Sigmoidal Kinetics of Glucokinase

“…One such mechanism is the property of glucokinase of having a Km value within the range of physiological concentrations of blood glucose [11,12,31], This feature allows the enzyme to adjust automatically its catalytic efficiency in response to the changing concentrations of glucose reaching the hepatocyte. Although a hyperbolic saturation function for glu cose has been reported for glucokinase [11,14,21,22,26], the description of some abnormalities [11,21] has encouraged us to further investigate the kinetics of the enzyme. In this paper, data will be presented indicating that glucokinase exhibits a sigmoidal saturation function.…”