What is the function of iodoacetate in protein chemistry?

Iodoacetate serves a specific function in protein chemistry by reacting with free thiol (-SH) groups in cysteine residues, leading to the addition of a carboxymethyl group to those sulfhydryl groups. This modification is a form of alkylation, where iodoacetate transforms the reactive thiol into a more stable carboxymethyl-thiol derivative, effectively blocking the thiol group from participating in further reactions or forming disulfide bonds. This is particularly useful in studies aiming to analyze protein structure and function by preventing thiol oxidation or the formation of intermolecular disulfide bonds.

The other options describe functions that do not align with the role of iodoacetate. Reducing disulfide bonds refers to the action of reducing agents that cleave S-S linkages, while labeling the N-terminus involves different reagents that specifically bind to the terminal amino group of proteins. Stabilizing α-helices involves interactions such as hydrogen bonds or hydrophobic effects, which are unrelated to the activity of iodoacetate. These distinctions clarify why adding a carboxymethyl group to free -SH groups is the primary role of iodoacetate in protein chemistry.