Chymotrypsin Mechanism

1)

Substrate binds to the hydrophobic pocket

2)

Histidine acts as a general base to active a serine OH group

3)

A serine alkoxide ion attacks a carbonyl carbon of the substrate, forming a covalent acyl bond between enzyme and substrate.

4) and 9)

A tetrahedral transition state involving an oxyanion is stabilized by the oxyanion hole.

5)

Histidine acts as a general acid to protonate an amide nitrogen. The peptide bond is broken and the first product dissociates.

6)

Water enters the active site

7)

Histidine acts a general base to convert water into a hydroxide ion

8)

A hydroxide ion attacks the acyl bond between substrate and enzyme.

10)

Histidine acts as a general acid to protonate the serine oxygen group, breaking the acyl bond between enzyme and substrate. The second product dissociates.

What type of amino acids are found in the binding site of trypsin?

Asparate and glutamate (negatively charged side chains, where hydorphobic pocket attaches).