Final answer:
The isoelectric point of arginine is pH 5.61.
Step-by-step explanation:
The isoelectric point (pI) of an amino acid like arginine is the pH at which the molecule has a net charge of zero. To calculate the pI of arginine, we need to consider the pKa values of its functional groups: carboxyl group (-COOH), amino group (-NH2), and guanidino group (-NH=C(NH2)NH2).
The pKa values for the carboxyl group, amino group, and guanidino group in arginine are approximately 2.17, 9.04, and 12.48, respectively. To determine the pI, we look for the two pKa values that are closest together. In this case, the carboxyl group and the amino group are closest with a difference of 6.87 units. So, we take their average to find the pI: (2.17 + 9.04) / 2 = 5.605.
Therefore, the isoelectric point of arginine is approximately pH 5.61.