Leupeptin is a reversible competitive inhibitor of serine and thiol proteases. It has been reported to inhibit calpain, cathepsin B, cathepsins H, L and trypsin. Typical working concentrations are in the range of 10 to 100 µM. Leupeptin appears to be equally effective in any salt form, adjusting for equivalent peptide content. The hemisulfate salts were the first to be commercially available. Of the three salts, the hydrochloride is the least invasive form in biological settings. No problem or preference for the trifluoroacetate (TFA) form has been noted; TFA is volatile, so could possibly be removed by lyophilization.
Microbially produced leupeptin inhibitor was first isolated as a mixture of two very similar forms: acetyl-LeuLeu-Arg-al and propionyl-Leu-Leu-Arg-al. Although the propionyl leupeptin is active as an inhibitor the acetyl form is more commonly used and is available in several different forms. Leupeptin, because of its aldehyde group, may act as a reducing agent and therefore interfere in protein determinations such as Lowry and, to a lesser extent, Bradford.
Leupeptin stock (20 mg/ml): Leupeptin in Methanol. Prepare a stock of 20 mg/ml in methanol, Store at -20°C.
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