The object of the present invention is to provide a novel thiosulfonate compound, a reversible cationization agent for protein and/or peptide, which can reversibly cationize a wider range of proteins and peptides with high stability of quality and accuracy and which are useful for a high degree of purification and recovery, as well as, a method for solubilization for protein and/or peptide using the agent.The present invention is a thiosulfonate compound having three or more cations derived from a quaternary ammonium group within one molecule.
