Which of the following proteins has the highest isoelectric point (pI)?

The isoelectric point (pI) of a protein is the pH at which the protein carries no net electrical charge. Among the proteins listed, IgG has the highest isoelectric point due to its unique amino acid composition and structure. Immunoglobulin G (IgG) is a type of antibody found in blood and extracellular fluid, and it plays a crucial role in immune responses.

The pI of a protein is influenced by the presence and quantities of acidic and basic amino acids. IgG contains a higher proportion of basic amino acids such as lysine and arginine compared to the other proteins listed, which contributes to a higher pI. Consequently, at physiological pH, IgG will have a greater positive charge than proteins with lower pIs, such as albumin or transferrin.

Albumin generally has a lower pI due to its relatively high amount of acidic amino acids. Transferrin, while also a transport protein like albumin, has its own amino acid composition that yields a lower pI than that of IgG. Ceruloplasmin, which binds copper and has enzymatic functions, also has a lower pI compared to IgG due to similar compositional factors.

In terms of practical relevance