Chapter 3-3. Regulation of Enzyme’s Allosteric Stereoselectivity (allosteric regulation)
Higher category : 【Biology】 Chapter 3. Cell and Metabolism
※ The text summarized here is an excerpt specifically extracted from the “Chapter 3. Cell and Metabolism” on allosteric regulation.
A. Regulatory Molecules
⑴ Regulatory molecules refer to small molecules that bind to proteins and change their spatial structure, thereby altering the protein’s function.
⑵ Regulatory molecules are different from substrates.
⑶ Regulatory molecules include inhibitors and activators.
B. Allosteric Regulation (Stereoselectivity at Different Sites)
⑴ Allosteric regulation refers to the binding of an activator or inhibitor to a site other than the substrate-binding site of an enzyme, thereby activating or inhibiting the substrate’s reaction.
⑵ The site other than the substrate-binding site is called the allosteric site.
⑶ Allosteric regulation occurs in enzymes involved in irreversible reactions.
⑷ In cellular respiration, ATP acts as an inhibitor on enzymes involved in cellular respiration, while ADP acts as an activator, ensuring the appropriate level of cellular respiration.
C. Application 1: Noncompetitive Inhibition
⑴ Typical allosteric regulation does not completely block the reaction like noncompetitive inhibition.
⑵ When an inhibitor binds to an enzyme, causing allosteric regulation at a different site, it is called noncompetitive inhibition.
⑶ Competitive inhibitors bind to the active site where the substrate binds, not to a different site, so it is not allosteric regulation.
D. Application 2: Feedback Inhibition
⑴ Feedback inhibition refers to the mechanism where the final product inhibits the enzyme that acted in the early stages of a pathway, thereby regulating the metabolic pathway.
E. Distinction: Cooperativity
⑴ Cooperativity refers to the regulation of enzyme activity by the substrate itself instead of inhibitors or activators.
⑵ Positive cooperativity: Due to cooperativity, when one substrate molecule binds to the enzyme, it becomes easier for additional substrate molecules to bind.
⑶ Negative cooperativity: It exists but is extremely rare.
⑷ Hemoglobin is an example of cooperativity.
① Hemoglobin consists of four subunits, each having one oxygen-binding site.
② When one oxygen molecule binds to a binding site, the affinity for oxygen increases in the remaining binding sites.
③ However, once an oxygen molecule starts to detach in one region, the others also detach.
Input: 2013.04.30 20:54
Modified: 2023.06.24 20:33