Phosphorylation of Glucose Immediately on entry into the cells, glucose combines with a
phosphate radical in accordance with the following reaction:
Glucose Glucose-6-phosphateglucokinase or hexokinase +ATP This phosphorylation is promoted mainly by the enzyme glucokinase in the liver and by
hexokinase in most other cells.
The phosphorylation of glucose is almost completely irreversible except in the liver cells, the renal
tubular epithelial cells, and the intestinal epithelial cells; in these cells, another enzyme, glucose phosphatase, is also available, and when this is activated, it can reverse the reaction. In most tissues of
the body, phosphorylation serves to capture the glucose in the cell.That is, because of its almost
instantaneous binding with phosphate, the glucose will not diffuse back out, except from those special
cells, especially liver cells, that have phosphatase.
