Which reagent will destroy secondary and tertiary structures but NOT the primary structure of a protein?

Disulfide bridges are covalent bonds formed between cysteine residues in a protein, contributing to the protein's tertiary structure. Breaking these disulfide bonds can disrupt the secondary and tertiary structures of the protein, but it does not affect the primary structure, which is the linear sequence of amino acids. Therefore, a reagent that removes disulfide bridges will affect the higher-order protein structures while leaving the primary structure intact.