Question

question 15 (1 point)
which of the following amino acids has the highest isoelectric point?
lysine
threonine
histidine
arginine
alanine

Explanation:

The isoelectric point (pI) of an amino acid depends on its side - chain. Lysine (pI ≈ 9.74), Threonine (pI ≈ 5.60), Histidine (pI ≈ 7.59), Arginine (pI ≈ 10.76), Alanine (pI ≈ 6.01). Arginine has a guanidinium group in its side - chain which is highly basic. This makes its pI the highest among the given amino acids as the pI of basic amino acids is calculated using the formula \(pI=\frac{pK_{a2}+pK_{R}}{2}\) (where \(pK_{R}\) is the dissociation constant of the basic side - chain). For arginine, with its very basic side - chain (\(pK_{R}\approx12.48\)), it results in the highest pI value.

Answer:

Arginine