What characterizes cooperative enzyme interactions?

• A. Binding of substrate to one site reduces affinity at other sites.
• B. Binding of substrate to one site increases the rate of binding at additional sites.
• C. Enzymes function only with one molecule.
• D. Activation requires ATP hydrolysis.

Answer: (B)

Cooperative enzyme interactions happen when binding at one site changes the shape of other sites so they become more likely to bind substrate. This positive cooperativity makes the enzyme more active as more substrate molecules bind, often producing a sigmoidal (S-shaped) curve of activity versus substrate concentration. When the first substrate molecule binds, the enzyme shifts to a form with higher affinity for the remaining sites, so subsequent bindings occur more readily and the overall rate climbs quickly with increasing substrate.

That idea is captured by the statement that binding of substrate to one site increases the rate of binding at additional sites. The other options describe patterns that don’t match this cooperative behavior: one describes the opposite pattern (binding reduces affinity at other sites), and the remaining choices don’t describe cooperativity at all or imply an energy requirement not inherent to the cooperative phenomenon.