Answer to Question #240332 in Biochemistry for khadija

Question

How different amino acids act as acid or base catalyst during enzymatic reaction? Write the general acid (protonated) and base (deprotonated) form of following amino acids: Arginine, Tyrosine, Glutamate, Histidine, Serine, and Cysteine. How different amino acids act as acid or base catalyst during enzymatic reaction? Write the general acid (protonated) and base (deprotonated) form of following amino acids: Arginine, Tyrosine, Glutamate, Histidine, Serine, and Cysteine. 

Answer 1

How different amino acids act as acid or base catalyst during enzymatic reaction?

Enzymes are proteins that act as biological catalysts. Common organic reactions are catalyzed by them. Because of the amino and carboxyl functional groups, amino acids can behave as both an acid and a base. The isoelectric point is the pH at which a certain amino acid occurs in solution as a zwitterion (pI)

 Write the general acid (protonated) and base (deprotonated) form of following amino acids: Arginine, Tyrosine, Glutamate, Histidine, Serine, and Cysteine.

 The unprotonated versions of the amino acids listed above can catalyze general base catalysis:, Glutamate, Histidine, Tyrosine, Cysteine At different times in an enzyme cycle, a single amino acid residue can engage in both general acid and general base catalysis.

Amino acids have titrable amino (pKa 9.0-10.5) and carboxyl (pKa 2.0-2.4) groups on their own. The amino group is protonated at neutral pH, while the carboxyl group is deprotonated. Titration can also be done on the side chains of acid and basic amino acids, as well as some polar amino acids.:

Amino acid

Functional Group

Side chain pKa

Cysteine

-SH

8.3

Serine

-OH

13

Tyrosine

-OH

10.1

Glutamic acid

-COOH

4.3

Histidine

Imidazole ring

6.0

Arginine

Guanidino

12.5