Proteinase K Ultrapure (100 mg)

A recombinant subtilisin-related serine protease from QIAGEN, derived from the fungus Parengyodontium album (Tritirachium album) and expressed in Komagataella phaffii (Pichia pastoris). The 28.9 kDa enzyme is supplied as a lyophilized powder and is used to digest proteins, including DNases and RNases, during nucleic acid preparations without compromising DNA or RNA integrity.

The Ultrapure grade provides enhanced purity and solubility, with a reported 2.5-fold increase in solubility. The enzyme is highly soluble in water (≥50 mg/ml) and contains minimal residual DNA (≤0.1 pg/mg). Activity is specified at ≥35 U/mg lyophilizate and ≥45 U/mg protein, and the enzyme maintains these specifications for at least 24 months in its original, unopened container when stored at –20°C.

It functions across a working pH range of 4.0–12.0 with optimum activity at pH 7.5–8.5, and a working temperature range of 20–65°C with optimum activity at 50–56°C. Typical use is at 50–200 µg/mL in nucleic acid preparations at pH 7.5–8.5 and 37–55°C, with incubation times of 30 minutes to 18 hours. Activity is stimulated by 0.2–1% SDS or 1–4 M urea, and by Ca2+ at 1–6 mM, which also limits autolysis and increases thermal stability.

The protease cleaves preferentially behind hydrophobic amino acids, with the smallest hydrolyzed substrate being a tetrapeptide. It is not inactivated by chelating agents (e.g., EDTA), chaotropic salts, detergents, metal ions, thiol reagents, or trypsin-specific inhibitors, and can be inactivated by heating above 65°C or by using inhibitors such as PMSF or DIFP.