Proteinase K (20 mg)

This QIAGEN lyophilized powder enzyme is a subtilisin-related serine protease, supplied as a recombinant Proteinase K from Parengyodontium album (Tritirachium album). The 28.9 kDa protein is expressed in Komagataella phaffii (Pichia pastoris) and acts as a broad-spectrum endopeptidase for highly effective protein digestion across many laboratory applications.

Upon arrival, the lyophilized powder should be stored at –20°C. When kept in its original, unopened container, it maintains activity of ≥ 30 U/mg and specific activity of ≥40 U/mg for at least 24 months. One unit hydrolyzes urea-denatured hemoglobin, producing color equivalent to 1 µmol tyrosine per 1 min at 37°C and pH 7.5 by the Folin & Ciocalteu's method, with 1 U = 1 mAnsonU.

The enzyme is typically used at 50–200 µg/mL with nucleic acid preparations at pH 7.5–8.5 and 37–55°C, with incubation times ranging from 30 minutes to 18 hours. It cleaves proteins preferentially behind hydrophobic amino acids, with the smallest peptide hydrolyzed being a tetrapeptide. The working pH range is 4.0–12.0, with optimum activity at pH 7.5–8.5; full activity is maintained over several hours within pH 6.5–10.0. The working temperature range is 20–65°C, with optimum activity at 50–56°C. Activity is stimulated by 0.2–1% SDS or 1–4 M urea, while 1–6 mM Ca2+ protects the enzyme from autolysis and increases thermal stability. The enzyme is not inactivated by chelating agents (e.g., EDTA), chaotropic salts, detergents, metal ions, thiol reagents, or trypsin-specific inhibitors. It can be denatured by phenol extraction or inactivated by heating above 65°C, or with inhibitors such as PMSF or DIFP.