Proteinase K (1 ml)

This ready-to-use solution from QIAGEN is a recombinant broad-spectrum endopeptidase and subtilisin-related serine protease derived from Parengyodontium album (Tritirachium album) and expressed in Komagataella phaffii (Pichia pastoris) as a 28.9 kDa protein. It is certified RNase-free and DNase-free, with a declared DNA content of ≤200 pg/mL, an activity of ≥800 U/mL, and a documented minimum shelf life of at least 24 months in the original unopened container.

The enzyme offers broad substrate specificity and remains active across wide-ranging conditions. Working pH range is 4.0–12.0 with optimum activity at pH 7.5–8.5, and full activity is maintained over several hours between pH 6.5–10.0. Working temperature range is 20–65°C with optimum activity at 50–56°C. The storage buffer is composed of 10 mM Tris-HCl pH 7.5, 1 mM (CH₃COO)₂Ca, and 50% glycerol; upon arrival the product should be stored at –20°C, +4°C, or room temperature and not above 25°C.

Typical use is at 50–200 µg/mL for nucleic acid preparations at pH 7.5–8.5 and 37–55°C, with incubation times from 30 min to 18 h. The enzyme cleaves proteins preferentially behind hydrophobic amino acids and is stimulated by denaturing agents such as 0.2–1% SDS or 1–4 M urea. Ca²⁺ at 1–6 mM protects against 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, making it well suited for efficient digestion of proteins including DNases and RNases during nucleic acid preparation.