True statements about glucokinase is/are:
|A||Km value is higher than normal blood sugar|
|B||Found in liver|
|C||G-6P inhibits it|
|D||Has both glucose 6 phosphatase and kinase activity|
Difference between Hexokinase and glucokinase
- Phosphorylate any of the hexoses (non- specific),
- Found in all tissues
- Allosterically inhibited by Glucost-6-Phosphate
- Km is low, and high affinity for glucose
- No change with glucose feeding
- Inhibited by glucocorticoids and GH
- Main function is to make glucose available to tissues for oxidation at lower blood glucose level.
- Phosphorylate glucose only (specific)
- physiologically more labile
- Found only in liver and Pancreatic — Beta islet-cells
- Not inhibited by G-6-P
- Km is high and low affinity for glucose
- Increased after feeding of glucose after fasting
- Inhibited by Gluco-corticoids and GH
- Main function is to clear glucose from blood after meals and at blood levels> 100 mg/dL
In suilin this aeturty of Hexokinase II & IV
Glucokinase and Hexokinase →phosphorylate Glucose to G-6-P with help of ATP and Mg++. This is an irreversible reaction. i.e. they cannot release glucose from G-6-P
a. Glucose is released from G-6-P (last step of glycogenolysis) by Glucose-6-Phosphatase (present in Liver and kidney but absent in muscles)
a. Presents in Liver, pancreatic B-cells, small intestine
b. Not under direct control of Insulin
c. β-islet cells are freely permeable to glucose via GLUT-2 transporter.
d. Insulin, indirectly induces the glucokinase - this increases the phosphorylation of glucose - so that intracellular free glucose conc. stays low - facilitating the entry of glucose.
• GLUT-4 → present in Heart and skeletal muscles and Adipose tissue → Insulin stimulated uptake of glucose.