What is known as positive cooperativity in enzyme interactions?

Positive cooperativity refers to a phenomenon observed in certain enzymes and multi-subunit proteins where the binding of a substrate to one active site increases the affinity of the remaining active sites for the substrate. This process is often illustrated through the sigmoidal shape of the enzyme's saturation curve, which contrasts with the hyperbolic curve seen in non-cooperative binding.

When the first substrate molecule binds to the enzyme, it induces a conformational change in the enzyme's structure. This change can enhance the binding ability of additional substrate molecules to the remaining active sites. Essentially, the enzyme becomes more "receptive" to substrate as more binding occurs, resulting in a more efficient catalytic process as substrate concentrations increase.

This concept is crucial for understanding regulatory mechanisms in metabolic pathways, where enzymes that exhibit positive cooperativity can respond more effectively to changes in substrate concentrations, facilitating a more finely-tuned biological response.