What is proteinase k?
Proteinase K is a broad-specificity serine protease widely used in molecular biology. It digests proteins during sample preparation and helps reduce proteinaceous contaminants in nucleic-acid workflows.
Proteinase K is not a nuclease. It supports nucleic-acid preparation through protein digestion rather than direct DNA or RNA removal.
The key idea
Protein removal must be paired with a plan for the enzyme itself before the next analytical step.
[3]
Core properties and EC classification
An EC number classifies a catalysed reaction. It does not specify a production strain, amino-acid sequence, preparation purity or operating optimum. Related proteins can perform the same classified reaction, while a commercial activity name may cover several reactions.
· Classification · Accepted activity · Reaction scope
· EC 3.4.21.64 · peptidase K · Hydrolysis of keratin, and of other proteins with subtilisin-like specificity. Hydrolyses peptide amides
· Substrate / system · Chemical distinction · Practical interpretation
· Proteinase K · Broad proteolysis · Useful in sample preparation
· Nuclease · Nucleic-acid cleavage · Different substrate and purpose
· Residual active protease · Continued protein digestion · Potential interference with downstream enzymes
[3]
Molecular weight: monomer, dimer or multimer?
A monomer contains one protein subunit; a homodimer contains two copies of the same subunit, and a higher oligomer contains more. A protein domain is a region within a chain, not an additional subunit. Likewise, mixing enzymes in a bottle does not establish that they form a stable molecular complex.
· Property of the named example · Evidence and interpretation
· Molecular weight of the example · Approximately 29.0 kDa for the deposited protein entity (one polypeptide; PDB 1IC6). This is not whole-formulation mass or a measured glycosylated mass.
· Monomer, dimer or multimer? · Monomer, as annotated for PDB 1IC6 biological assembly 1.
· Model and experimental resolution · PDB 1IC6; 0.98 Å X-ray diffraction; representative chain A.
· Deposited protein sequence · 279 residues in the experimental entity; unresolved coordinates and biological processing are separate considerations.
· Construct annotation · Deposited mutations: S207D. Interpret this as the reported experimental construct.
The mass above is the deposited polypeptide-entity value. Glycosylation, precursor processing, linkers or omitted domains can change the experimentally observed mass. SDS–PAGE primarily informs denatured subunit size; native assembly needs evidence such as SEC–MALS, analytical ultracentrifugation or an appropriate structural analysis. The viewer shows one selected chain for clarity, not necessarily the complete biological assembly.
[1][2]
FROM MOLECULE TO APPLICATIONProtein removal must be paired with a plan for the enzyme itself before the next analytical step.
Natural sources and fermentation hosts
The historical fungal source is Tritirachium album; Engyodontium album is used in the structural record. Taxonomic name changes should be distinguished from changes in enzyme identity.
Fungal production and recombinant fermentation are both relevant. For molecular-biology use, purity, contaminating nuclease activities and formulation matter alongside the expression host.
· Term · What it means in this report
· Natural donor of the model · Engyodontium album — the organism associated with the displayed protein sequence.
· Expression host of the structural sample · Not separately specified in this structural record; do not infer a recombinant host.
· Manufacturing route · Fungal production and recombinant fermentation are both relevant. For molecular-biology use, purity, contaminating nuclease activities and formulation matter alongside the expression host.
· Supplied product · Use the linked product documentation for the actual grade, activity assay and declared source. A structural example does not establish the manufacturing organism or purity of the supplied preparation.
[1]
Reaction mechanism and structure–function relationships
A subtilisin-family aspartate–histidine–serine triad forms and hydrolyses an acyl-enzyme intermediate. Calcium supports structural stability rather than acting as the peptide-cleaving nucleophile. Detergent, chaotrope and temperature tolerance depend on specified conditions; resistance is not unlimited.
THE REACTION, STEP BY STEP
1
Bind an accessible peptide region
2
Form the serine acyl-enzyme intermediate
3
Hydrolyse and release peptide fragments
Proteins + water→Peptide fragments
Conceptual reaction pathway; the stages describe function rather than atomic geometry.
From active-site chemistry to a useful process
Protein removal must be paired with a plan for the enzyme itself before the next analytical step. Use a matched sample without protease and assess both protein removal and the downstream assay. A clean electrophoretic protein profile is helpful but does not replace testing whether residual preparation components interfere with the intended analysis.
The catalytic mechanism explains which chemical transformation is possible. It does not, by itself, establish the rate in a complex material. Substrate presentation, reaction-medium composition and retention of the active fold determine whether that chemistry can proceed usefully under the chosen conditions. This is why a defined-substrate activity measurement and an application trial provide complementary evidence.
[2][3]
Discovery and scientific milestones
Discovery, purification, structural characterisation and industrial adoption are different historical milestones. The named studies below identify specific contributions; a publication date is not automatically the first discovery of every activity covered by the enzyme name.
1974
Biochemical and historical context
Ebeling and colleagues described proteinase K from Tritirachium album in 1974. The name and broad proteolytic properties became established in biochemical and molecular-biology methods.
[3]2001
Betzel and colleagues: molecular characterisation
The primary study associated with PDB 1IC6 is “Structure of a serine protease proteinase K from Tritirachium album limber at 0.98 A resolution.”. The experimental structure links the named protein to a concrete molecular model, allowing its fold, substrate-binding region and assembly to be examined rather than inferred from the general enzyme name.
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Major industrial applications and research uses
DNA and RNA extraction, tissue lysis and analytical sample preparation use proteinase K. Residual protease may damage downstream protein reagents, so removal or inactivation must match the subsequent workflow.
01
Nucleic-acid extraction
Remove protein components during lysis.
Measure success: Assess nucleic-acid integrity and downstream performance.
02
Analytical preparation
Reduce protein contamination.
Measure success: Confirm removal or compatible inactivation.
03
Protein-digestion research
Investigate accessibility and digestion patterns.
Measure success: Track fragmentation over time.
A research use, a development-stage process and an established commercial application do not imply the same level of readiness. Match the preparation to the target matrix and required grade, then validate the specific outcome described above. The product links below provide the route from this scientific overview to a defined supplied formulation.
Activity assays and interpreting experimental results
Casein or peptide assays quantify proteolysis, but nucleic-acid workflows also require appropriate contaminant specifications. Compare digestion on the actual sample matrix; protein concentration alone does not establish activity or reagent suitability.
A useful experiment for this enzyme
Use a matched sample without protease and assess both protein removal and the downstream assay. A clean electrophoretic protein profile is helpful but does not replace testing whether residual preparation components interfere with the intended analysis.
· Experimental question · Evidence to collect
· Is the enzyme active? · Measure an initial rate with a defined substrate, blank correction and a stated activity-unit definition.
· Does it work on this material? · Assess nucleic-acid integrity and downstream performance.
· Is the preparation stable? · Measure residual activity after a specified exposure, separately from activity during the exposure.
· Is the product what you intended? · Confirm removal or compatible inactivation.
Keep enzyme loading, substrate amount, mixing, temperature and sampling time explicit. Use a no-enzyme control to capture non-enzymatic changes and a suitable analytical blank for colour, background sugars, peptides or other interfering components. A time course is more informative than one endpoint when the reaction slows, because substrate depletion, loss of activity and product effects can produce similar plateaus.
Reading kinetic and operating data
Compare reported pH and temperature optima only when substrate and assay duration are comparable. An optimum describes the measured rate within an experiment; it is not a guarantee of long-incubation stability. For heterogeneous substrates, changes in accessibility can also affect apparent kinetic behaviour. Cite the protein, substrate and conditions alongside any kinetic constant rather than treating it as a universal property of the enzyme name.
[3]
Common questions
Does proteinase K directly digest DNA?
Its defining activity is proteolysis, not DNA hydrolysis.
Is it active under every denaturing condition?
No. Tolerance must be established for the actual detergent, chaotrope and temperature.
Can residual enzyme affect PCR reagents?
Residual protease can damage protein reagents; the workflow should remove or inactivate it appropriately.
Continue exploring
Proteinase K for Protein Removal: Designing a Compatible Workflow ↗Acid protease deep dive ↗Neutral protease deep dive ↗Alkaline protease deep dive ↗
