ENZYME REGULATION

This chapter discusses several mechanisms by which enzymes may be modulated for the purpose of cellular regulation of activity. It argues that enzymes can undergo positive and negative modulation, resulting in activation and inhibition of activity, respectively. The regulation of catalytic activity for many enzymes can be understood in terms of a simple, two-state model, in which the enzyme exists in either the inactive state (I) or the active state. Posttranslational modification refers to any process by which the initial protein that is translated from mRNA by the ribosome is covalently altered in ways that may affect the structure and/or function of the protein. The catalytic activity of enzymes can be positively or negatively regulated by protein–protein interactions that occur intramolecularly between domains, intermolecularly between the enzyme and other proteins, or by oligomerization of the enzyme.