Britannica
Sources used in this answer
How does cooperativity affect substrate binding in enzymes with several subunits?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
Enzyme
In the induced-fit theory of enzyme-substrate binding, a substrate approaches the surface of an enzyme (step 1 in box A, B, C) and causes a change in the enzyme shape that results in the correct alignment of the catalytic groups (triangles A and B; circles C and D represent substrate-binding groups on the enzyme that are essential for catalytic activity). The catalytic groups react with the substrate to form products (step 2). The products then separate from the enzyme, freeing it to repeat the sequence (step 3). Boxes D and E represent examples of molecules that are too large or too small for proper catalytic alignment. Boxes F and G demonstrate binding of an inhibitor molecule (I and I′) to an allosteric site, thereby preventing interaction of the enzyme with the substrate. Box H illustrates binding of an allosteric activator (X), a nonsubstrate molecule capable of reacting with the enzyme.
In enzymes composed of multiple subunits, cooperativity describes how the binding of a substrate to one subunit alters the shape of neighboring subunits, thereby influencing their affinity for subsequent substrate molecules.1
This interaction occurs in two primary ways:
- Positive Cooperativity: The binding of a substrate molecule to the first subunit induces a conformational change that makes it easier for subsequent substrate molecules to bind to the remaining subunits.1
- Negative Cooperativity: The binding of a substrate to the first subunit makes it more difficult for additional substrate molecules to bind to the other subunits.1
This process is a key aspect of allosteric control, allowing enzymes to regulate their activity levels based on the concentration of available substrate.12