Question

Amino acids occasionally are used as buffers. A buffer is a solution that resists changes in pH when acid or base are added. The pH range over which a buffer is effective is called the buffering range, usually defined as pKa + 1 to pKa -1.

a. Indicate the buffering range (or ranges) of Gly, His, Asp and Lys .

b. Choose an amino acid to buffer at pH = 4, pH =6, pH =9, and pH =12.

c. Would you expect a protein containing 100 amino acids to be as good a buffer as its constituent free amino acids at equivalent molar amino acid concentrations? Explain.

Answer 1

A) Buffering range of Glycine(Gly) = 2.2-3.6

Buffering range of Histidine(His) = 5.5-7.4

Buffering range of Aspartic acid(Asp) = 1.88-3.65

Buffering range of Lysine(Lys) = 9.5-10.0

B) Amino acid to buffer at pH 4= Aspartic acid and Glutamic acid

Amino acid to buffer at pH 6 is Histidine

Amini acid to buffer at pH 9 and 12 is glycine.

C) A protein containing 100 amino acid is as good as buffer as its constituent free amino acid because Each protein peptide has an amine N-terminal which can serve as base and carboxy C-terminal which can serve as acid. Proteins have side chains of which many can be protonated and deprotonated, they can serve as good buffer.