Aprotinin

CAS No:	9087-70-1
EINECS No:	232-994-9
Synonyms:	Basic trypsin inhibitor, bovine pancreatic trypsin inhibitor (BPTI), kallikrein inactivator, kunitz-type trypsin inhibitor, MGC148815, pancreatic trypsin inhibitor, protease inhibitor from bovine lung, PTI, serine protease inhibitor aprotinin, TKI, Trasylol® (brand name), trypsin-kallikrein inhibitor

Product Summary

Aprotinin is a well-characterized, potent serine protease inhibitor derived from bovine lung. With its small size, tight structure, and high stability, it effectively inhibits several key proteases involved in proteolysis, coagulation, and inflammation. It is widely used in biochemistry and biomedical research to protect proteins from degradation and to study protease function and regulation.

Formula: C₂₈₄H₄₃₂N₈₄O₇₉S₇

Molecular weight: ~6512 Da

Function

Aprotinin is a broad-spectrum serine protease inhibitor that inhibits enzymes such as:

Trypsin
Chymotrypsin
Plasmin
Kallikrein
Elastase (weakly)

Mechanism of Action

Reversible binding to active sites
The inhibitory activity of aprotinin is largely due to its ability to mimic the natural substrate of the enzyme: Aprotinin presents a specific peptide loop (around its Lys15–Ala16 sequence) that mimics the enzyme's substrate. This loop fits precisely into the S1 specificity pocket of serine proteases, which is typically the primary binding site for the positively charged residue (e.g., lysine or arginine) of the substrate. This substrate-like conformation allows aprotinin to be recognized and bound by the enzyme as if it were a real substrate. Aprotinin binds to the active site of the target serine protease in a reversible manner, meaning the interaction is non-covalent and can be dissociated under the right conditions (e.g., dilution, change in pH or ionic strength)
Formation of a tight, non-covalent enzyme-inhibitor complex
Once docked into the active site, aprotinin forms a high-affinity, non-covalent complex with the enzyme: The inhibitor interacts with the catalytic triad (usually Ser-His-Asp) in the active site of the protease. However, because aprotinin is structurally stabilized by three internal disulfide bridges, it resists proteolytic cleavage, effectively "freezing" the enzyme in an inactive complex. The resulting complex is exceptionally stable (with dissociation constants in the sub-nanomolar range), thus effectively blocking the enzyme’s activity even at low concentrations.
Inhibition of proteolytic activity
By occupying the active site, aprotinin prevents access of natural substrates to the catalytic triad. Halts hydrolysis of peptide bonds by the enzyme. Suppresses downstream proteolytic cascades, such as fibrinolysis or kallikrein-mediated inflammatory responses.

Applications in Scientific Research

Biochemical and molecular research
Aprotinin is widely used in biochemical laboratories for its ability to inhibit unwanted proteolysis during experimental procedures. In many sample preparation protocols, endogenous proteases can be released and activated, leading to the degradation of target proteins. Aprotinin helps to preserve protein integrity in the following contexts:
- Cell lysis: When cells are disrupted (mechanically or chemically), intracellular proteases are released. Aprotinin prevents these enzymes from degrading cytosolic or membrane-bound proteins.
- Protein purification: During affinity chromatography or other purification steps, proteins are exposed to environments where proteases may be active. Aprotinin maintains target protein stability and bioactivity.
- Tissue homogenization: Homogenization of tissue (e.g., brain, liver, muscle) can lead to the release of proteolytic enzymes. Adding aprotinin ensures the integrity of delicate signaling proteins, enzymes, or receptors.
- Protease Inhibition Cocktails: Aprotinin is a key component in commercial and custom-made protease inhibitor cocktails used in protein extraction buffers, often in combination with leupeptin, pepstatin A, and EDTA, to provide broad-spectrum protection against serine and other classes of proteases.
Cell biology
Aprotinin is used in cell culture and tissue engineering experiments where proteolytic regulation of the extracellular environment is critical:
- Extracellular matrix (ECM) remodeling: Aprotinin is employed to modulate proteolytic activity in studies involving collagen, fibronectin, or matrix metalloproteinase (MMP) activity.
- Inflammation studies: By inhibiting kallikrein, aprotinin helps investigate the regulation of inflammatory mediators such as bradykinin and prostaglandins.
- Angiogenesis research: Aprotinin modulates protease-driven processes that influence endothelial cell migration and neovascularization, making it useful in angiogenesis assays and cancer metastasis studies.
Hematology and thrombosis research
Aprotinin is instrumental in coagulation and fibrinolysis research due to its ability to block serine proteases involved in blood clotting:
- Fibrinolysis inhibition: Aprotinin inhibits plasmin, the main enzyme responsible for breaking down fibrin clots, and is used to study the regulation of clot stability and breakdown.
- Coagulation cascade studies: By inhibiting kallikrein, aprotinin indirectly affects the intrinsic coagulation pathway and contact system, helping researchers dissect the roles of individual proteases.
- Kallikrein-Kinin System Research: Aprotinin serves as a tool to explore the production of bradykinin, a potent vasodilator, by blocking the cleavage of kininogen by kallikrein.
Enzyme kinetics and mechanistic studies
- Aprotinin is a model Kunitz-type protease inhibitor, often used in kinetic assays to determine inhibition constants (Ki) of serine proteases.
- It helps establish enzyme specificity, catalytic rates, and inhibitor binding modes by serving as a well-characterized competitive inhibitor.
- Crystallography and NMR studies involving aprotinin–enzyme complexes are fundamental in understanding enzyme-inhibitor interactions and are cited in numerous structural biology publications.
Tissue and organ preservation
- Aprotinin has been investigated for its role in organ transplantation, particularly in kidney, liver, and pancreas preservation..
- During cold ischemia, proteases released from damaged cells can degrade structural and functional proteins. Aprotinin inclusion in preservation solutions helps reduce enzymatic degradation and improves post-transplant outcomes.

Packaging & Storage

Sources: purified from bovine lungs
Available as white to off-white hygroscopic powder
Store in an airtight tamper-proof container, protected from light, at a temperature of 2°C to 8°C

References

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