Final answer:
The approximate isoelectric point (pI) of the peptide ARLHTEDM is likely around 6.0 due to the presence of a basic residue (Arginine) and two acidic residues (Glutamic acid and Aspartic acid), with the other amino acids having pIs around the neutral range. Therefore, correct option is b.
Step-by-step explanation:
To determine the approximate isoelectric point (pI) of the peptide ARLHTEDM, we need to look at the amino acids that compose the peptide and their relative pIs. Specifically, we are interested in the ionizable side chains that could contribute to the overall charge of the peptide at different pH levels.
Amino acids with basic side chains (e.g., Arginine), tend to have higher pIs, whereas those with acidic side chains (e.g., Aspartic acid and Glutamic acid) have lower pIs.
Here we have Arginine (R), which is basic, and two acidic residues, Glutamic acid (E) and Aspartic acid (D). The high pI of Arginine will be balanced against the low pIs of the acidic residues.
The other amino acids present (Alanine (A), Leucine (L), Histidine (H), Threonine (T), Methionine (M)) typically have pIs near the neutral range (around 5 to 6.5 when their side chains are neutral).
Considering the collective effect of all these residues, one might anticipate the pI of the peptide to be somewhere near neutral, but skewed slightly towards the acidic side due to there being more acidic residues than basic ones.
Therefore, the best estimate for this peptide would be closer to option (b) 6.0, which is a typical pI for a peptide with a small excess of acidic residues.