Question

Put these steps in the mechanism of chymotrypsin catalysis in order from first to last. Note that your textbook may not break out each of these steps individually, but all steps should be ordered. (There will be eight steps.) A. His 57 catalyzes removal of H from Ser 195 hydroxyl. B. His 57 donates H to N of sissile peptide bond, tetrahedral intermediate decomposes. C. The portion (N-terminal end) of the original substrate with the new carboxylate terminus diffuses away. D. Water donates H to His 57. E. Resulting OH attacks carbonyl of remaining substrate. F. His 57 donates H to Ser 195 O, leading to collapse of thtrahedral intermediate. G. the portion (the C-terminal end) of original substrate with the new amino terminus diffuses away. H. Ser 195's nucleophilic O attacks carbonyl C of substrate.

Answer 1

Concepts and reason

Chymotrypsin is a protease enzyme that causes the proteolysis or breakdown of the proteins and polypeptides. Chymotrypsin cleaves the carbonyl side of certain peptides by covalent catalysis.

Being site specific chymotrypsin will only cleave the carboxyl side of large hydrophobic amino acids such as tyrosine, methionine, phenylalanine, and tryptophan, unless it is followed by a proline.

Fundamentals

Chymotrypsin preferentially cleaves the bulky hydrophobic amino acids due to the formation of S1 pockets.

The covalent catalysis of chymotrypsin includes acylation that forms acyl-enzyme intermediate. This intermediate undergoes deacylation process converting back to its original free enzyme form.

The covalent catalysis of chymotrypsin occurs in two steps, an acetylation phase and a deacylation phase. In, the acylation phase, the peptide bond is cleaved and ester is formed between substrate and enzyme. In, the deacylation phase, this ester is hydrolyzed and the enzyme is regenerated.

Ans:

The correct order is

1.His 57 catalyzes removal of H from Ser 195 hydroxyl (a)

2.Ser 195's nucleophilic O attacks carbonyl C of substrate (h)

3.His 57 donates H to N of sissile peptide bond, tetrahedral intermediate decomposes (b)

4.The portion (the C-terminal end) of original substrate with the new amino terminus diffuses away (g)

5.Water donates H to His 57 (d)

6.Resulting OH attacks carbonyl of remaining substrate (e)

7.His 57 donates H to Ser 195 O, leading to collapse of the tetrahedral intermediate (f)

8.The portion (N-terminal end) of the original substrate with the new carboxylate terminus diffuses away (c)

Answer 2

His 57 catalyzes removal of H from Ser 195 hydroxyl
Ser 195's nucleophilic O attacks carbonyl C of substrate
His 57 donates H to N of scissile peptide bond, tetrahedral intermediate decomposes
The portion (C terminal end) of original substrate with the new amino terminus diffuses away
Water donates H to His 57
Resulting OH attacks carbonyl of remaining substrate
His 57 donates H to Ser 195 O, leading to collapse of tetrahedral intermediate
The portion (n terminal end) of original substrate with the new carboxylate terminus diffuses away