What is described by the term 'homotropic regulation of binding'?

Homotropic regulation of binding refers to a scenario in which the substrate of an enzyme also acts as a regulator of its activity. In this context, when the substrate binds to one site on an enzyme, it influences the binding of additional substrate molecules to other sites on the same enzyme. This type of regulation typically involves cooperative binding, where the initial binding of the substrate enhances the likelihood of subsequent substrate binding due to conformational changes in the enzyme.

This concept is particularly important in allosteric enzymes, which often exhibit cooperative binding behavior. When the substrate binds, it stabilizes an active conformation of the enzyme, making it easier for more substrate molecules to bind, thus increasing the overall enzyme activity in a regulated manner.

In contrast, other types of regulation involve different dynamics. For instance, allosteric regulators that are not substrates would fall under heterotropic regulation, and regulatory molecules that inhibit enzyme activity typically do not enhance substrate binding. Additionally, binding that affects only one subunit of the enzyme typically pertains to non-cooperative interactions, which do not fit the definition of homotropic regulation where the binding influences multiple sites.