Question

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

Short answer

Answer: Aspartate (Asp) and Glutamate (Glu) can form salt linkages with the side chain of lysine at pH 7.4.

Step-by-step solution

Analyzing Lysine

At pH 7.4, the side chain of lysine (\(\text{NH}_3^\oplus\)) will be positively charged as the -NH3 group will capture a proton (H+).

Identify Amino Acids with Negatively Charged Side Chains at pH 7.4

To form a salt linkage, the positively charged lysine side chain must interact with a negatively charged amino acid side chain. There are two main amino acids with negatively charged side chains at pH 7.4. These are: 1. Aspartate (Asp): With a side chain of -CH2-COO-, it loses a proton (H+) at pH 7.4, forming a negatively charged -COO- group. 2. Glutamate (Glu): With a side chain of -CH2-CH2-COO-, it also loses a proton (H+) at pH 7.4, forming a negatively charged -COO- group.

Determine Amino Acids Capable of Forming Salt Linkages with Lysine

The amino acid side chains that can form salt linkages with the side chain of lysine at pH 7.4 are Aspartate (Asp) and Glutamate (Glu). The positively charged side chain of lysine will form an ionic bond (salt linkage) with the negatively charged side chains of these amino acids.