What are enzyme cascades?

An enzyme cascade is a sequence of enzymes where the substrate for the subsequent enzyme is the product of the previous one.

An enzyme cascade can have three different types of regulation: feedback from products that inhibit the activity of enzymes further back in the cascade, control through a "feed-forward" mechanism, and a rate-limiting step where the enzyme catalyzes the slowest reaction of the cascade.

One ligand (primary message) outside the cell binds to one receptor in G-protein coupled receptor cell signaling, so one ligand activates one receptor. This is an example of how some enzyme cascades can also result in an amplification of the signal.

The G protein, which is an enzyme because it contains GTPase activity, is stimulated by the activated receptor to exchange GTP for GDP. This activation of the G protein then triggers the activation of another enzyme, such as adenylyl cyclase, which generates a large number of cAMP molecules.

Thus, a single ligand activated numerous G proteins, which in turn activated numerous adenylyl cyclase molecules, producing numerous cAMP molecules.

After that, many molecules of protein kinase A, another enzyme in the cascade, can be activated by cAMP molecules. This can phosphorylate many proteins, which can then regulate other enzymes in the cell.

This is an example of signal amplification within an enzyme cascade: from one ligand molecule outside the cell activating one receptor, we may be activating hundreds or even thousands of proteins inside the cell.

Enzyme cascades are sequential biochemical reactions where the product of one enzyme serves as the substrate for the next enzyme in the pathway. This sequential activation amplifies the signal and allows for precise regulation of cellular processes. Enzyme cascades are often involved in signal transduction pathways, where extracellular signals are transmitted into the cell to elicit specific responses.