Cathepsin

Updated: 2026-09-15

Overview

Cathepsins are a group of proteolytic enzymes primarily located in lysosomes, responsible for breaking down proteins during cellular turnover. They are classified into serine (e.g., Cathepsin A), cysteine (e.g., Cathepsin B, L), and aspartic (e.g., Cathepsin D) proteases based on their catalytic mechanisms. These enzymes function optimally at acidic pH (4.5–6.0) and are synthesized as inactive zymogens, requiring activation in lysosomes. Research highlights their involvement in critical biological processes, including immune response modulation via MHC class II antigen presentation and extracellular matrix degradation during metastasis. Dysregulation of cathepsin activity is linked to pathologies such as osteoporosis, cancer progression, and neurodegenerative disorders like Alzheimer’s disease.

Physical and Chemical Properties

Cathepsins exhibit distinct physicochemical properties depending on their subclass. Cysteine cathepsins (e.g., Cathepsin B) contain a catalytic diad of cysteine and histidine residues, while aspartic cathepsins (e.g., Cathepsin D) rely on two aspartate residues. Their molecular weights range from 20 kDa (monomeric forms) to 40 kDa (glycosylated variants), with isoelectric points between pH 5.0–7.5. Stability varies: cysteine cathepsins are sensitive to oxidation and require reducing agents (e.g., DTT) for activity, whereas serine cathepsins are more stable in neutral buffers. Most isoforms lose activity above 37°C or at neutral-to-alkaline pH, necessitating strict storage at -20°C in glycerol or lyophilized form.

Main Applications

In biotechnology, cathepsins are utilized for protein digestion in mass spectrometry sample preparation and epitope mapping. Pharmaceutical applications include targeting cathepsin K (inhibitors for osteoporosis) and Cathepsin S (autoimmune disease therapeutics). Cancer research leverages their role in tumor invasion, with Cathepsin B serving as a biomarker for aggressive carcinomas. Industrial uses extend to food processing, where Cathepsin L tenderizes meat, and in cheese ripening via Cathepsin D’s casein hydrolysis. Diagnostic kits employ isoform-specific substrates (e.g., Z-FR-AMC for Cathepsin B) to quantify enzyme activity in clinical samples.

Safety and Storage

Cathepsins require careful handling due to their proteolytic nature. Use PPE (gloves, goggles) to prevent skin/eye contact. Cysteine cathepsins are particularly hazardous if inhaled as powders. Store lyophilized enzymes at -20°C in desiccated conditions; reconstituted solutions should include stabilizers (e.g., 1 mM EDTA, 5 mM DTT) and be aliquoted to avoid contamination. For disposal, autoclave or treat with 1% bleach to denature active enzymes. SDS-PAGE analysis is recommended to confirm purity before use, as contaminants may skew experimental results. Activity assays (e.g., fluorogenic substrates) should validate functional integrity post-thawing.

B2B Procurement Guide

When sourcing cathepsins, prioritize suppliers with ISO 13485 certification for diagnostic-grade enzymes or GMP compliance for therapeutic applications. Key specifications include activity units (e.g., μmol/min/mg), purity (>95% by SDS-PAGE), and absence of endotoxins (<0.1 EU/μg) for in vivo studies. Bulk buyers should request batch-specific CoA (Certificate of Analysis) and stability data. Recombinant isoforms (e.g., human Cathepsin L from E. coli) offer consistency but may lack post-translational modifications present in native forms. Lead times vary: 2–4 weeks for common isoforms, longer for custom modifications (e.g., fluorescent labeling).