BIO Lecture 4: Regulation of Enzymes

Inside a cell, an enzyme is subject to a variety of factors that influence its behavior. Metabolic pathways in the cell are not always on and must be tightly regulated to maintain health. Therefore, the activity of key enzymes in metabolic pathways is usually regulated in one or more of the following ways:
1. Covalent modification: addition of a phosphate group by a protein kinase--this can activate or deactivate an enzyme. Note that this is always a reversible modification
2. Proteolytic cleavage: many enzymes are synthesized in inactive forms (zymogens) that are activated by cleavage by a protease
3. Association with other polypeptides: some enzymes have catalytic activity in one polypeptide subunit that is regulated by association with a separate regulatory subunit. If you remove the regulatory subunit then continuous rapid catalysis results from the catalytic subunit (known as constitutive activity)
4. Allosteric Regulation: modification of active site activity through interactions of molecules with other specific sites on the enzyme known as allosteric sites

ALLOSTERIC REGULATION: means at another place. The binding of the allosteric regulator to the allosteric site is generally noncovalent and reversible. In other words, small molecules bind to particular sites on an enzyme that are different from the active site.

Feedback inhibition: negative feedback is the most common form of feedback regulation. Essentially, an end product will shut off an enzyme early in the pathway.