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