cross-linking study protein cross-linking with a bifunctional reagent MI:0031 Label transfer techniques bifunctional agent crosslink PSI-MI Cross-linking agents induce the formation of covalent bonds among proteins that are neighbours. The cross-linker may be a bifunctional molecule having two reactive ends linked by a spacer, often containing a disulfide bond. When a reducing agent is added the disulfide bridge is cleaved, the cross-linked pairs are released and can be identified. There are various classes of cross-linkers, the most common are those having photoreactive groups that become reactive fluorophores when activated by UV light thereby resulting in photolabeling the cross-linked moieties. Photoaffinity labelling