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Proteinase K
from Engyodontium album
(formerly Tritirachium album)
for Molecular Biology
Catalog Number P2308
Storage Temperature –20 °C
CAS RN 39450-01-6
E.C. 3.4.21.64
Synonym: Endoproteinase K
Product Description
Proteinase K is a stable serine protease with broad
substrate specificity. It degrades many proteins in the
native state even in the presence of detergents.
Proteinase K was isolated from a fungus able to grow
on keratin and the enzyme can digest native keratin
(hair), hence, the name "Proteinase K".
1
Evidence from
crystal and molecular structure studies indicates the
enzyme belongs to the subtilisin family with an active-
site catalytic triad (Asp
39
, His
69
, Ser
224
). The
predominant site of cleavage is the peptide bond
adjacent to the carboxyl group of aliphatic and aromatic
amino acids with blocked alpha amino groups. It is
commonly used for its broad specificity.2-4
The mode
and specificity of action has been studied.4
Proteinase K is frequently used in molecular biology
applications to digest unwanted proteins, such as
nucleases from DNA or RNA preparations from
microorganisms, cultured cells, and plants.
5-11
The
enzyme is typically used at 50–200 µg/ml in nucleic
acid preparations at pH 7.5–8.0 and 37 °C. Incubation
times vary from 30 minutes to 18 hours. Proteinase K is
usually denatured by subsequent phenol extractions,
although it can autodigest during long incubations.3
Catalog Numbers P2308 and P4850 (a solution in 40%
(v/v) glycerol and Tris buffer) are tested for suitability in
molecular biology applications.
Proteinase K is active in 1% TRITON®
X-100 and fully
active in 0.5% (w/v) SDS. SDS and urea will denature
protein substrates resulting in increased digestion rates.
Proteinase K itself is denatured much more slowly by
these agents.3,12,13
Molecular mass: 28,930 Da (amino acid sequence)
14
28,500 Da (SDS-PAGE)
15
pH range:2,3
7.5–12.0 (urea-denatured hemoglobin as
substrate), but most often used in pH
range 7.5–9.0.
Temperature profile:3
maximum activity at 37 °C
(In the temperature range of 20–60 °C, a minimum
of 80% of the activity observed at 37 °C is
expected)
pI:2
8.9
Extinction coefficient:
2
E
1%
= 14.2 (280 nm,
10 mM NaCl and 5 mM CaCl2, pH 8.0)
Activators: 1–5 mM Ca2+
is required for activation.
When calcium is removed from the enzyme (addition of
EDTA) 25% of the catalytic activity is lost. However, if
the EDTA-Ca
2+
complex is removed from the enzyme
solution by gel filtration, a total of 80% of the enzyme
activity is lost and only a small activation will occur
upon addition of excess Ca
2+
to the Ca
2+
-free enzyme.
16
Inhibitors: Proteinase K is inhibited by DIFP or PMSF
(the latter used at final concentration 5 mM).
3
It is partly
inactivated, but not inhibited, by EDTA (see Activators).
Proteinase K is not inhibited by iodoacetic acid, the
trypsin-specific inhibitor TLCK, the chymotrypsin-
specific inhibitor TPCK, nor p-chloromercuribenzoate.
This product is supplied as a lyophilized powder.
Protein content: ≥90%
Specific activity: ≥30 units/mg of protein
Unit Definition: One unit will hydrolyze urea-denatured
hemoglobin to produce color equivalent to 1.0 µmole
(181 µg) of tyrosine per minute at pH 7.5 at 37 °C.
Impurities:
DNase – none detected
Endonuclease (nickase) – none detected
RNase – none detected
DNA – ≤500 picograms DNA/mg solid (<0.5 ppm)

Precautions and Disclaimer
This product is for R&D use only, not for drug,
household, or other uses. Please consult the Material
Safety Data Sheet for information regarding hazards
and safe handling practices.
Preparation Instructions
This product is soluble in water (1 mg/ml), yielding a
clear colorless solution.
Storage/Stability
Sigma recommends storage at –20 °C, though others
have claimed stability at 2–8 °C. When stored at
–20 °C, the product retains activity for at least 2 years.
A Proteinase K solution remains active over a broad pH
range (4.0–12.5, optimum pH 8.0) and also over the
temperature range of 25–65 °C during use. At pH 8.0,
solutions remain active for at least 12 months at
2–8 °C.
3
At pH 4–11.5, solutions containing Ca
2+
(1–6 mM) are expected to remain active for several
weeks. An 80% ammonium sulfate suspension stored
at 2–8 °C remains active for at least 12 months.
2
References
1. Betzel, C., Three Dimensional Structure of
Proteinase K at 0.15 nm Resolution. Eur. J.
Biochem., 178, 155-171 (1988).
2. Ebeling, W., et al., Proteinase K from Tritirachium
album Linder, Eur. J. Biochem., 47, 91 (1974).
3. Enzymes of Molecular Biology, vol. 16, Burrell,
M.M., ed. Humana Press (Totowa, NJ: 1993), p.
307.
4. Kraus, E., and Femfert, U., Proteinase K from the
Mold Tritirachium album Limber, Specificity and
Mode of Action. Z. Physiol. Chem., 357, 937
(1976).
5. Lizardi, P.M., and Engelberg, A., Rapid Isolation of
RNA Using Proteinase K and Sodium Perchlorate.
Anal. Biochem., 98, 116 (1979).
6. Gross-Bellard, et al., Isolation of High Molecular
Weight DNA from Mammalian Cells, Eur. J.
Biochem., 36, 32-38 (1973).
7. Molecular Cloning: A Laboratory Handbook, 2nd
ed., Sambrook et al., eds., Cold Spring Harbor
Press (Cold Spring Harbor, NY: 1989) p. 1.61 and
p. B.16.
8. Kasche, V., et al., A Two-step Procedure for
Quantitative Isolation of Pure Double-strand DNA
from Animal Tissues and Cell Cultures. Prep.
Biochem., 11, 233 (1981).
9. Hansen, J.N., Isolation of Higher Molecular Weight
DNA from Bacillus cereus T Using Proteinase K.
Prep. Biochem., 4, 473 (1974).
10. Holm, C., et al., A Rapid, Efficient Method for
Isolating DNA from Yeast. Gene, 42, 169 (1986).
11. La Claire, J.W., and Herrin, D.L., Co-isolation of
High-Quality DNA and RNA from Coenocytic Green
Algae. Plant Mol. Biol. Reporter, 15, 263 (1997).
12. Hilz, H., et al., Stimulation of Proteinase K action by
Denaturing Agents: Application to the Isolation of
Nucleic Acids and the degradation of “Masked”
Proteins. Eur. J. Biochem., 56, 103 (1975).
13. Methods of Enzymatic Analysis, 3
rd
Edition,
Bergmeyer, H.U., ed., Academic Press (New York,
NY: 1983) vol. 2, p. 299.
14. Jany, K.D., et al., Amino Acid Sequence of
Proteinase K from the Mold, Tritirachium album
Linder. Proteinase K; a Subtilisin-related Enzyme
with Disulfide Bonds. FEBS Letters, 199, 139
(1986).
15. Jany, K.D., and Mayer, B., Proteinase K from
Tritirachium album linder, Molecular Mass and
Sequence Around the Active Serine Residue. Biol.
Chem. Hoppe-Seyler, 366, 485 (1985).
16. Bajorath, J., et al., The Enzymatic Efficiency of
Proteinase K is Controlled by Calcium. Eur. J.
Biochem., 176, 441-447 (1988).
TRITON is a registered trademark of Union Carbide
Corp.
RBR,RBG,MAM 12/08-1
Sigma brand products are sold through Sigma-Aldrich, Inc.
Sigma-Aldrich, Inc. warrants that its products conform to the information contained in this and other Sigma-Aldrich publications. Purchaser
must determine the suitability of the product(s) for their particular use. Additional terms and conditions may apply. Please see reverse side of
the invoice or packing slip.

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