Leupeptin, also known as N-acetyl-L-leucyl-L-leucyl-L-argininal, is a naturally occurring protease inhibitor

Protease inhibitor

Protease inhibitor can refer to:* Protease inhibitor : a class of medication that inhibits viral protease* Protease inhibitor : molecules that inhibit proteases...

 that can inhibit cysteine, serine and threonine peptidases.

It is often used during in vitro experiments when a specific enzymatic reaction is being studied. When cells are lysed for these studies, protease

Protease

A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....

s, many of which are contained within lysosome

Lysosome

thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleoli]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] rough [[endoplasmic reticulum]]...

s, are released. These proteases, if freely present in the lysate, would destroy any products from the reaction being studied, and make the experiment uninterpretable. For example, leupeptin could be used in a calpain

Calpain

A calpain is a protein belonging to the family of calcium-dependent, non-lysosomal cysteine proteases expressed ubiquitously in mammals and many other organisms. Calpains constitute the C2 family of protease clan CA in the MEROPS database...

 extraction to keep calpain from being hydrolyzed by specific proteases. The suggested concentration is 1-10 µM (0.5-5 µg/ml).

Leupeptin is an organic compound produced by actinomycetes, which inhibits serine

Serine protease

Serine proteases are enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the active site.They are found ubiquitously in both eukaryotes and prokaryotes...

, cysteine

Cysteine protease

Proteases are enzymes that degrade polypeptides. Cysteine proteases have a common catalytic mechanism that involves a nucleophilic cysteine thiol in a catalytic dyad. The first step is deprotonation of a thiol in the enzyme's active site by an adjacent amino acid with a basic side chain, usually a...

 and threonine protease

Threonine protease

Threnonine proteases are a family of proteolytic enzymes harbouring a threonine residue within the active site.The prototype members of this class of enzymes are the catalytic subunits of the proteasome....

s. Leupeptin inhibits serine proteinases (trypsin

Trypsin

Trypsin is a serine protease found in the digestive system of many vertebrates, where it hydrolyses proteins. Trypsin is produced in the pancreas as the inactive proenzyme trypsinogen. Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine, except when...

 (K_i=3.5 nM), plasmin

Plasmin

Plasmin is an important enzyme present in blood that degrades many blood plasma proteins, most notably, fibrin clots. The degradation of fibrin is termed fibrinolysis. In humans, the plasmin protein is encoded by the PLG gene.- Function :...

 (K_i= 3.4 nM), porcine kallikrein

Kallikrein

Kallikreins are a subgroup of serine proteases, enzymes capable of cleaving peptide bonds in proteins. In humans, plasma kallikrein has no known homologue, while tissue kallikrein-related peptidases encode a family of fifteen closely related serine proteases...

), and cysteine proteinases (papain

Papain

Papain, also known as papaya proteinase I, is a cysteine protease enzyme present in papaya and mountain papaya .-Papain family:...

, cathepsin

Cathepsin

Cathepsins are proteases: proteins that break apart other proteins, found in many types of cells including those in all animals. There are approximately a dozen members of this family, which are distinguished by their structure, catalytic mechanism, and which proteins they cleave...

 B (K_i = 4.1 nM), endoproteinase Lys-C

Endoproteinase Lys-C

Endoproteinase Lys-C is a protease that cleaves proteins on the C-terminal side of lysine amino acids....

). It does not inhibit α-chymotrypsin

Chymotrypsin

Chymotrypsin is a digestive enzyme that can perform proteolysis. Chymotrypsin preferentially cleaves peptide amide bonds where the carboxyl side of the amide bond is a tyrosine, tryptophan, or phenylalanine. These amino acids contain an aromatic ring in their sidechain that fits into a...

 or thrombin

Thrombin

Thrombin is a "trypsin-like" serine protease protein that in humans is encoded by the F2 gene. Prothrombin is proteolytically cleaved to form thrombin in the first step of the coagulation cascade, which ultimately results in the stemming of blood loss...

. Leupeptin is a competitive transition state inhibitor and its inhibition may be relieved by an excess of substrate.

Leupeptin is soluble in water (stable for 1 week at 4 °C and 1 month at -20 °C), ethanol, acetic acid and DMF.

It can be given topically for middle and inner ear infections.