1. Suppose chymotrypsin is labeled by producing an enzyme that contains a partic

Question

1. Suppose chymotrypsin is labeled by producing an enzyme that contains a particular residue as radioactive. This allows the enzyme to be ‘followed’ throughout experiments and identified easily. Think about the atoms that get ‘labeled’ and the position of these labels throughout each reaction cycle.

E. Your colleague proposes labeling chymotrypsin by tritiating the oxyanion hole. Is this possible? Would these labels disappear after the first reaction cycle? What are the atoms in the oxyanion hole capable of doing, in certain circumstances?

Explanation / Answer

An oxyanion hole is a pocket in the active site of enzyme which has both catalytic site and binding site. It is a region in space where the backbone amide hydrogen, where amide groups are positioned in such a way that a tetrahedral enzyme substrate intermediate is stabilized. The oxyanion hole increases the activity of the enzyme increases upto 10,000 times the substrate concentration.

Chymotrypsin mechanism is as follows:

1.Binding of substrate to the active site of enzyme

2.formation of tetrahedral intermediates

3.formation of aceyl enzyme intermediate

4.removal of amide product and addition of water

5.deacylation

6.removal of carboxylate product

The tetrahedral intermediate collapses and the acyl intermediate is formed. The first reaction product is where amide groups breaks and the process further continues..

Reaction would be differentiated if atoms were labeled initially due to radioactive nature of substances. Yes this is possible hypothetically.

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