In liver parenchymal cells and β cells of the pan- creas, glucokinase (also called hexokinase D , or type IV ) is the predominant enzyme responsible for the phosphorylation of glu- cose. In β cells, glucokinase functions as the glucose sensor, determining the threshold for insulin secretion (see p. 310). In the liver, the enzyme facilitates glucose phosphorylation during hyper- glycemia. [Note: Hexokinase also serves as a glucose sensor in neurons of the hypothalamus, playing a key role in the adrenergic response to hypoglycemia