CONCEPT 8.5: Regulation of enzyme activity helps control metabolism
• Chemical chaos would result if a cell’s metabolic pathways were operating
simultaneously
• Cells can regulate metabolic pathways by switching on or off the genes that encode
specific enzymes, or by regulating the activity of existing enzymes
Allosteric Regulation of Enzymes
• Allosteric regulation occurs when a regulatory molecule binds to a protein at one site
and affects the protein’s function at another site
• This type of regulation may either inhibit or stimulate enzyme activity
Allosteric Activation and Inhibition
• Most allosterically regulated enzymes are made from polypeptide subunits, each with its
own active site
• The complex oscillates between two shapes, one catalytically active and the other
inactive
• An activating or inhibiting molecule may bind to a regulatory site, often located where
the subunits join
• The binding of an activator stabilizes the shape that has functional active sites, whereas
the binding of an inhibitor stabilizes the inactive form of the enzyme
• In cooperativity, substrate binding to one active site triggers a shape change in the
enzyme that stabilizes the active form for all other sites
• This mechanism amplifies the response by priming the enzyme to act on additional
substrate molecules more readily
• Chemical chaos would result if a cell’s metabolic pathways were operating
simultaneously
• Cells can regulate metabolic pathways by switching on or off the genes that encode
specific enzymes, or by regulating the activity of existing enzymes
Allosteric Regulation of Enzymes
• Allosteric regulation occurs when a regulatory molecule binds to a protein at one site
and affects the protein’s function at another site
• This type of regulation may either inhibit or stimulate enzyme activity
Allosteric Activation and Inhibition
• Most allosterically regulated enzymes are made from polypeptide subunits, each with its
own active site
• The complex oscillates between two shapes, one catalytically active and the other
inactive
• An activating or inhibiting molecule may bind to a regulatory site, often located where
the subunits join
• The binding of an activator stabilizes the shape that has functional active sites, whereas
the binding of an inhibitor stabilizes the inactive form of the enzyme
• In cooperativity, substrate binding to one active site triggers a shape change in the
enzyme that stabilizes the active form for all other sites
• This mechanism amplifies the response by priming the enzyme to act on additional
substrate molecules more readily
