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Ch6 Enzyme - Coggle Diagram
Ch6 Enzyme
Chymotrypsin 胰蛋白酶 Mechanism
(1) substrate binding :substrate 塞進chymotrypsin的His57 的N release e-, e-
(2)nucleophilic attack: form Hb
(3)substrate cleavage分裂 ：the amino leaving group is protonated by His57 , facilitate its displacement (一部分離開,一部分留在裡面）
(4) water comes in: provide H+ , taking on negative charge
(5)Water attacks:collapse of the tetrahedral intermediate forms the second product , a carboxylate anion, and displaces Ser195
(6)break off from the enzyme
(7)product dissociation (regenerate free enzyme): substrate & chymotrypsin分開
Cleavage of peptideoglycan by lysozyme(Sn2)
What are they?
Peptidoglycan
polysaccharide
Found in many bacteria cell wall
Lysozyme
An antibacterial enzyme (need H2O 的O)*
(1)Asp52 acts as nucleophile to attack the anomeric carbon
(2)Glu35 acts as a general acid(getH+)
(3) water hydrolyze the covalent glycosyl-enzyme intermediate
(4)Glu35 act as a general base(deprotonate water in the second Sn2 step)
Ending:generate product(可脫離)
Enzyme inhibition
Inhibitors
Irreversible : powerful toxin
Reversible: used as medicine
Competitive inhibition
搶結合位
Vm不變 Km⬆️ 親和力⬇️
Not affect catalysis
Uncompetitive inhibition
Enzyme-substrate 結合物。抑制整個反應
Vm⬇️ Km⬇️ Km/Vm不變
Inhibit: catalytic function
Mixed inhibition
Intersect line
Vm⬇️
Inhibit: substrate binding& catalysis
Noncompetitive inhibition
Vm⬇️ Km不變
Regulate
Noncovalent modificarion(allosteric)異位調控
Allosteric effectors usually small chemical
Allosteric effectors可以促進也可抑制
Covalent modification: blood coagulation cascade (凝血機制)
Irreversible
Reversible
Catalytic mechanism
acid-base : give and take H+
Form H2O v.s. breakdown of intermediate
Form H2O faster : not increase the rate
Breakdown faster: the alternative proton donors or acceptors increase the rate of reaction
Covalent: change reaction path (鍵結改變）require a nucleophile(provide e- ) ex. Serine, thiolate, amine, carboxylate
metal ion :[O] [R]
Enzyme Kinetics動力論
Sequential Kinetic Mechanism(連續型）
lines intersect（相交）
Km⬇️ 親和力⬆️ Vm⬆️
Ping-pong kinetic Mechanism
Parallel 平行
Km⬆️親和力⬇️
特性
Enzyme do not affect Keq
increase reaction rates by decreasing delta G
How to lower delta G
Close proximity
enzymes bind transition states best (enzymes bind transition states better than substrates) [proposed by Linus Pauling]
