The side chain of histidine has a typical pK a value in the range of 6.5-7.4. Ho

Question

The side chain of histidine has a typical pKa value in the range of 6.5-7.4. However, when analyzing the pKa values in a particular protein, scientists determined that one particular His residue has an unusually low pKa value of 4.8. Which of the following statements correctly explain this anomaly?

1) The microenvironment around a residue can impact its pKa value.
2) A positively charged amino acid must be in close proximity to this residue.
3) A negatively charged amino acid must be in close proximity to this residue.

4) This residue must be located on the surface of the protein.

Statements 1 and 2 are correct. Statements 1 and 4 are correct. Statements 1, 2, and 4 are correct. Statements 2, 3, and 4 are correct.

Explanation / Answer

Solution :-

1) The microenvironment around a residue can impact its pKa value.
2) A positively charged amino acid must be in close proximity to this residue.

so the answer is statement 1 and 2 are correct

because the environment can change the pka value and alsoo when the positively charged amino group is present therefore it acts as conjugate acid so it can decrease the pka

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