The ability to control enzyme activity is essential in cels in order to produce molecules when needed and conserve energy/resources. One way to reulate enzymes is through activators and inhibitors. These are molecules that alter the enzyme's conformation or block the active site, and they are not involved in the reaction in any way. Heteroallosteric effectors are molecules that interact with allosteric enzymes and alter their activity. Enzymes can also be regulated through covalent modification by phosphorylation. The reversible addition of a phosphate group alters the conformation of the enzyme, increasing or decreasing activity by affecting substrate binding and/or ability to produce products. Kinases are proteins that add phosphate groups, and phosphatases are proteins that remove phosphate groups. The cleavage of an inactive enzyme is another form of regulation. Catalytically inactive precursors are cut to create the active enzyme. The activation of chymotrypsinogen to alpha-chymotrypsin is an example of this. Another form of enzyme regulation is through irreversible inhibitors. These molecules permanently impair enzyme activity, typically via covalent modification. Irreversible inhibitor usually, but not always, result in the complete loss of enzyme activity. On the other hand, reversible inhibitors are not permanent, and they come in three forms: competitive, uncompetitive, and noncompetitive/mixed. Competitive inhibitors bind to the active site and prevent substrate binding, but uncompetitive inhibitors only bind to the enzyme-substrate complex at a location other than the active site. Noncompetitive/mixed inhibitors are able to bind to the free enyme and the enzyme-subtrate complex at a location other than the active site, but not at the same time.
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