Summary
In the present study, the characterization of glucose phosphorylating activities in
islet extracts and the effect of fasting on these activities have been studied.
4 mM glucose 6-phosphate strongly inhibits hexokinase activity, while glucokinase
increased its activity. N-acetyl-glucosamine inhibits hexokinase activity (40% inhibition),
while glucokinase increased its activity (19% increment).
Both phosphorylating activities reaches a maximum when the Mg/ATP ratio is 1; increments
in Mg/ATP ratio inhibits glucokinase activity while hexokinase activity is less dependent
of Mg/ATP ratio.
Fasting induces a progressive decrease of both phosphorylating activities in islet
extracts. After 48 h fasting both activities are decreased 50%. After 96 h fasting,
glucokinase activity disappeared completely, while hexokinase was 80% reduced.
Our data suggest that hexokinase is less affected by fasting than glucokinase. In
addition, other authors have reported that other glycolytic enzymes are little altered
by fasting.
Hence the fasting-induced-adaptation of glucokinase could account for the reduced
rate of glycolysis and subsequently reduced insulin secretory response towards glucose.
Key-Words:
Islet
-
Glucokinase
-
Hexokinase
-
Fasting
-
Glucose-6-phosphate
-
N-Acetylglucosamine
-
Magnesium
