L-Alaninamide, N-[(phenylmethoxy)carbonyl]-L-valyl-N-[(1S)-1-(2-fluoroacetyl)-4-methoxy-4-oxobutyl]-

Z-VAE(OMe)-fmk is a cell-permeable and irreversible UCHL1 inhibitor. The inhibitor approaches the active-site cleft from the opposite side of the crossover loop as compared to the direction of approach of ubiquitin's C-terminal tail, thereby occupying the P1' (leaving group) site, a binding site perhaps used by the unknown C-terminal extension of ubiquitin in the actual in vivo substrate(s) of UCHL1.