Hexokinase and the induced fit model of enzyme activity



SCHOLAR : Biology : 1 Molecular Interactions in Cell Events: Catalysis : 1.3 Enzymes : 1.3.3 Enzyme properties :

Figure 9 shows an interactive model of the enzyme hexokinase. Hexokinase catalyses the formation of glucose-6-phosphate from glucose and ATP. In fact, there are two molecules of the enzyme on display in Figure 9 (in other words, it shows a dimer). A molecule of glucose is bound at the active site of the upper enzyme molecule and, as a result of induced fit, the enzyme has closed around the glucose molecule. The lower enzyme molecule does not contain glucose at the active site, and the structure of the enzyme is much more open.

Use the mouse to right-click over the model in Figure 9, choose Color from the menu that is shown, and click on Chain. Now you should be able to see the glucose molecule (which is red) within the (blue) enzyme. Rotating the model will help. Figure 10 may help you to understand the model in Figure 9.

The difference in shape between the two enzyme molecules is more obvious if you use the mouse to right-click over the model in Figure 9, choose Display from the menu that is shown, click on Spacefill and then Van der Waals Radii. The lower enzyme molecule has a deep groove exposing the active site; the upper enzyme molecule has closed around the active site.

Figure 9 - Molecular model of hexokinase.

Figure 10 - Wireframe model of hexokinase (dimer). The pink circle indicates the position of a glucose molecule in the upper enzyme molecule.