Question

At pH 7.4, with what amino acid side chains can the side chain of lysine form salt linkages?

Short answer

Answer: At pH 7.4, the side chain of lysine can form salt linkages with the side chains of aspartic acid (Asp) and glutamic acid (Glu). These ionic interactions occurring between the positively charged ammonium group (NH3+) of lysine and the negatively charged carboxylate groups (-COO-) of aspartic acid and glutamic acid.

Step-by-step solution

Understand the properties of lysine at pH 7.4

Lysine is a basic amino acid with a side chain that contains a primary amine group (NH2). At pH 7.4, which is close to the physiological pH, the amine group in the lysine side chain will be protonated, forming a positively charged ammonium group (NH3+).

Identify the types of side chains that can form salt linkages with lysine

Since the side chain of lysine is positively charged at pH 7.4, it can form salt linkages (also known as ionic interactions) with negatively charged (acidic) side chains.

Determine which amino acids have acidic side chains at pH 7.4

There are two primary amino acids with acidic side chains: aspartic acid (Asp) and glutamic acid (Glu). At pH 7.4, their carboxyl groups (-COOH) will be deprotonated, forming negatively charged groups (-COO-).

Summarize the amino acids that can form salt linkages with lysine

At pH 7.4, the side chain of lysine can form salt linkages with the side chains of aspartic acid (Asp) and glutamic acid (Glu). These ionic interactions take place between the positively charged ammonium group (NH3+) of lysine and the negatively charged carboxylate groups (-COO-) of aspartic acid and glutamic acid.