Merck, E3132-1MG, E-64

General description
E-64 is a cysteine protease inhibitor that was isolated from the mold Aspergillus japonicus TPR-64. E-64 is also known as N-[N-(L-3-trans-carboxyoxiran-2-carbonyl)-L-leucyl]-agmatine. E-64 effectively inhibits various cysteine proteases, in particular:
cathepsin K
cathepsin L
cathepsin S
E-64 also acts against other enzymes, such as:
calpain
cathepsin B
cathepsin H
papain

Application
E-64 is an effective ligand for affinity purification of cysteine proteases. When coupled to a thiolated affinity matrix, binding is no longer irreversible, but specificity is retained.
Biochem/physiol Actions
E-64 is an irreversible, potent, and highly selective cysteine protease inhibitor. E-64 does not react with the functional thiol group of non-protease enzymes, such as L-lactate dehydrogenase or creatine kinase. E-64 will not inhibit serine proteases (except trypsin) like other cysteine protease inhibitors, leupeptin and antipain. The trans-epoxysuccinyl group (active moiety) of E-64 irreversibly binds to an active thiol group in many cysteine proteases, such as papain, actinidase, and cathepsins B, H, and L to form a thioether linkage. E-64 is a very useful cysteine protease inhibitor for use in in vivo studies because it has a specific inhibition, it is permeable in cells and tissues and has low toxicity.
Effective irreversible inhibitor of cysteine proteases that does not affect cysteine residues in other enzymes or react with low molecular weight thiols such as calpain and cathepsin B. Effective concentration 1-10 μM.
Preparation Note
E-64 is soluble in water. A 20 mg/ml solution can be prepared in water (heat may be needed). A suggested stock solution is a 1 mM aqueous solution. The effective concentration for use as a protease inhibitor is 1 to10 μM. Aqueous stock solutions are stable for months at -20 °C. Diluted solutions are stable for days at neutral pH. E-64 is stable from pH 2-10, but is unstable in ammonia or in HCl. E-64 is also soluble in DMSO, a 10 mM solution can be prepared in dry DMSO and stored at -20 °C. Subsequent dilutions were in culture medium. Solutions for injection were prepared by dissolving E-64 in 0.9% sodium chloride or in a minimum amount of saturated sodium bicarbonate followed by dilution with 0.9% sodium chloride (after adjusting the pH to 7.0 with acetic acid).