GB123

GB123 is a fluorescent, non-quenched activity-based probe (ABP) designed to covalently target and label active cysteine cathepsins, specifically cathepsin B, cathepsin L, and cathepsin S. Developed by researchers at Stanford University, GB123 consists of a dipeptide recognition sequence (carboxybenzyl-phenylalanine-lysine, or Z-FK) linked to a reactive acyloxymethyl ketone (AOMK) electrophilic warhead and conjugated to a Cy5 near-infrared fluorophore. Upon binding to the active site of target cysteine proteases, the AOMK group undergoes nucleophilic attack by the active-site cysteine, resulting in irreversible covalent attachment of the probe and enabling direct optical imaging and biochemical profiling of active cathepsins in vitro, ex vivo, and in vivo. It has been widely used as a research tool to study cathepsin activity in cancer, atherosclerosis, pancreatitis, and epilepsy.

Other names

Cbz-Phe-Lys(Cy5)-AOMKZ-FK(Cy5)-AOMKZ-FK-AOMK-Cy5Z-FK-AOMK-Cy-5Z-FK-AOMK-Cy 5