TBR Bio Section VII, passage IX, question # 57

[zoner]

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according to the figures shown in the passage, why is lysozyme involved acid catalysis considered as noncovalent catalysis instead of covalent catalysis?

My reasoning was that since the H from Glu 35 is getting transfered and gets convalently attached to the carbon 4 of ring E, it is covalent catalysis...

Thanks in advance.

 

[Thirteeen]

Covalent bond involves the sharing of a pair of electrons and does not result from a complete transfer of electrons (ionic bond). In this case I don't see any sharing but a transfer. Also, covalent bonds are stronger and therefore won't be practical in catalysis.

 

[Rabolisk]

It is not considered covalent catalysis because there is no covalent bond between the substrate and the enzyme, only proton transfers. However...

Also, covalent bonds are stronger and therefore won't be practical in catalysis.

That is not true. Covalent catalysis is not as common as general acid-base catalysis, but it does occur.

 

[zoner]

I still don't get it. Proton is transfered and gets attached to the oxygen via covalent bond. If not, what bond is holding O and H together?

 

[Thirteeen]

It is not considered covalent catalysis because there is no covalent bond between the substrate and the enzyme, only proton transfers. However...



That is not true. Covalent catalysis is not as common as general acid-base catalysis, but it does occur.

Thanks for the correction. You are correct, in some cases it helps to reduce the energy of the subsequent transition state. 🙂