Defining the Induced Fit Model
The induced fit model is a theory of enzyme-substrate interaction that proposes the active site of an enzyme is flexible and not perfectly complementary to the substrate before binding. According to this model, the binding of the substrate induces a conformational change in the enzyme's active site, leading to a more precise fit.
Section 2: How It Works
Unlike the rigid 'lock and key' model, the induced fit model suggests a dynamic interaction. When a substrate approaches the enzyme, the amino acid side chains that make up the active site are rearranged to mold around the substrate. This dynamic adjustment not only ensures a snug fit but also positions the substrate optimally for the catalytic reaction to occur, often by stabilizing the transition state.
Section 3: A Practical Example
A classic example of the induced fit model is the enzyme hexokinase, which phosphorylates glucose. Before glucose binds, the active site is in a more open conformation. Upon binding, the enzyme's two lobes close around the glucose molecule. This conformational change excludes water from the active site and brings the catalytic groups into the correct alignment to transfer a phosphate group from ATP to glucose.
Section 4: Importance of the Model
The induced fit model is crucial because it more accurately explains the specificity and catalytic efficiency of most enzymes. It accounts for the ability of some enzymes to bind to a range of similar substrates and provides a better understanding of how allosteric regulators can change an enzyme's activity by altering the shape of its active site.