Chymotrypsin Mechanism: Correct Steps for Enzymatic Catalysis

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The discussion focuses on the correct steps in the enzymatic catalysis mechanism of chymotrypsin. Key steps include the activation of Ser 195 by His 57, which facilitates the nucleophilic attack on the substrate's carbonyl carbon. The formation and collapse of a tetrahedral intermediate are crucial, leading to the release of the C-terminal portion of the substrate. Water then plays a role in regenerating the active site, allowing for the attack on the remaining substrate. Questions arise about the nucleophilicity of Ser 195 and the substrate's presence in the reaction center after its initial involvement.
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what are the correct steps for the mechanism of chymotrypsin?

Below is my answer but I don't know if it is right.


a) His 57 catalyzes removal of H from Ser 195 hydroxyl.
b. Ser 195's nucleophilic O attacks carbonyl C of substrate.
c. His 57 donates H to N of sissile peptide bond, tetrahedral intermediate decomposes.
d. C- terminal portion of oribinal substrate with its new amino acid terminus diffuses away.
e. water donates H to His 57.
f. Resulting OH attacks carbonyl of remaining substrate.
g. His 57 donates H to Ser 195 O, leading to collapse of tetrahedral intermediate.
h.N-terminal portion of original substrate with its new carboxy terminus diffuses away.

My answer is b,a,c,e,f,g,h,d. Is this right? Thank you! :)
 
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Two comments/questions:

Why do you believe that the O of Ser195 would be nucleophilic before its proton was partially abstracted by His57?

Why do you believe that the substrate would remain in the reaction center if it is no longer involved in the reaction after step c?
 
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