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Biochemistry - Lecture 10 (01/03/2017)
Enzyme Regulation and Inhibition
Allosteric enzyme control.
Noncovalent allosteric regulation
Most key metabolic control enzymes are usually 'Allosteric'.
Most Allosteric enzymes have a Quaternary structure.
Allosteric enzymes exhibit 'cooperativity' between their subunits.
Allosteric enzymes have a second regulatory site (allosteric site) distinct from the Active site.
Allosteric inhibitors or activators bind to this site and regulate enzyme activity via conformational changes.
Cooperativity between subunits
What is 'cooperativity'?
Cooperativity describes how the binding of a substrate to one active site subsequently affects the binding of all the other subunits (Usually converting them to their more active form).
The plots of rate versus substrate concentration are sigmoidal in nature due to this subunit cooperativity (ie: Vo versus [S] plots are not hyperbolic).
Allosteric Activation and Inhibition
An allosteric enzyme has active and inactive forms:
The binding of an activator stabilizes the active form
(R form) [Relaxed] of the enzyme (High affinity form).
The binding of an inhibitor stabilizes the inactive form (T form) [Tight] of the enzyme (Low affinity form).
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