Protein modification reagents generally include reagents that add, cleave, or reduce.

Reagents that add labels are used for immunoassays, flow cytometry, fluorescence-activated cell sorter (FACS) analysis, and molecular function and structure studies. Addition reagents also include those used to block particular functional groups. Enzymatic cleavage reagents remove amino acids, produce antibody fragments, and release peptides from fusion proteins. Reducing agents are used for protein solubilization, label transfer applications, and to facilitate cross-linking.