Z-FA-FMK is a control peptidic fluoromethylketone (boc-Thr-CH2F), and inhibitor to calpain (Ac-Leu-Leu-norleucinal), cathepsin B (Z-Phe-Ala-CH2F), and CPP32-like proteases (Z-DEVD-CH2F) [1]. A peptidyl fluoromethyl ketone (cathepsin B) was found to be an effective compound in a time dependent inactivation of cathepsin B isozymes from a number of tissues including human tumors [2]. The inhibitor of cathepsins B and L Z-FA-fmk blocks the induction of DEVDase activity, DNA fragmentation, and externalization of phosphatidylserine by selective RRMs. Z-FA-FMK can inhibit caspase activity in vitro and selectively inhibits recombinant effector caspases 2, -3, -6, and -7. In contrast, purified initiator caspases 8 and 10 are not affected, whereas the apoptosome-associated caspase 9 is only partially inhibited by Z-FA-FMK in vitro. [3]

It is an inhibitor of cysteine proteases, such as cathepsin B, which do not require a P1 Asp residue. It may be used as a negative control inhibitor for FMK P1 Asp caspase inhibitors.

References:
1. Inhibition of the interleukin-1 beta converting enzyme family rescues neurons from apoptotic death. Lynch, T., Vasilakos, J.P., Raser, K., Keane, K.M., Shivers, B.D. Mol. Psychiatry (1997)
2. Visualization of time-dependent inactivation of human tumor cathepsin B isozymes by a peptidyl fluoromethyl ketone using a fluorescent print technique. Smith, R.E., Rasnick, D., Burdick, C.O., Cho, K.J., Rose, J.C., Vahratian, A. Anticancer Res. (1988)
3. Lopez-Hernandez, F. J., Ortiz, M. A., Bayon, Y., & Piedrafita, F. J. (2003). Z-FA-fmk Inhibits Effector Caspases but not Initiator Caspases 8 and 10, and Demonstrates That Novel Anticancer Retinoid-related Molecules Induce Apoptosis via the Intrinsic Pathway1.Molecular cancer therapeutics, 2(3), 255-263.