Human Topoisomerase I

• Human DNA Topoisomerase I (Topo I) - a type IB topoisomerase that relaxes supercoiled DNA during replication and transcription
• Essential enzyme for maintaining DNA topology and a key target for anticancer research
• Produced by recombinant expression in baculovirus-infected insect cells (Spodoptera frugiperda)
• Purified using optimised protocols adapted from Stewart et al. (1996) for native-like performance
• Supplied as a high-purity, activity-validated enzyme in Dilution Buffer
• Includes 10X Assay Buffer and Dilution Buffers (available separately)
• 1 Unit relaxes 0.5 µg of supercoiled pBR322 DNA in 30 minutes at 37°C
• Ideal for relaxation assays, mechanistic studies, and inhibitor screening in drug discovery
• Enables comparative studies across type I and type II topoisomerases
• Strict quality control ensures accuracy, reproducibility and batch consistency
• Store at -80°C for long-term stability and dependable activity
• Bulk and custom quantities available on request for larger-scale research

Human Topoisomerase I is a type IB topoisomerase that plays an essential role in regulating DNA topology. The enzyme relaxes supercoiled DNA by transiently cleaving, allowing the controlled rotation of the DNA before rejoining the cleaved strand of the DNA duplex, thereby relieving torsional stress generated during replication and transcription. Because of its central function in DNA metabolism, human topoisomerase I is a widely studied enzyme and an important target for anticancer drugs, including camptothecin derivatives.

Our recombinant human Topoisomerase I is produced by overexpressing the enzyme in baculovirus-infected insect cells (Spodoptera frugiperda) and purifying it using methods adapted from Stewart et al., 1996. This system provides high-quality enzyme preparations that closely reflect native human activity. The enzyme is supplied in dilution buffer and validated for activity, purity and stability.

Enzymatic activity

One Unit of human Topoisomerase I relaxes 0.5 µg of supercoiled pBR322 DNA in 1X assay buffer in a 30 µl reaction volume at 37°C for 30 minutes. This well-defined activity standard allows researchers to achieve reproducible results across different experiments and laboratories.

Product format

Each preparation is supplied with:

• Recombinant human Topoisomerase I enzyme in dilution buffer
• 10X concentrated assay buffer
• Additional  assay and dilution buffer, available separately

Applications

Human Topoisomerase I is suitable for a wide range of research uses, including:

• Relaxation assays with supercoiled DNA
• Mechanistic studies of DNA strand passage and re-ligation
• Screening of topoisomerase I inhibitors for anticancer research
• Comparative studies with other type I and type II topoisomerases

Storage and supply

The enzyme should be stored at –80°C for long-term stability. 

All batches of human Topoisomerase I are produced under strict quality control, with technical documents and lot-specific data supplied to ensure accuracy and reproducibility.

Larger quantities and bulk supply are available on request - get in touch

FAQs about Human Topoisomerase I

What is human Topoisomerase I and what does it do?
Human DNA Topoisomerase I (Topo I) is a type IB enzyme that relaxes supercoiled DNA by transiently cleaving, allowing controlled rotation and rejoining the cleaved strand of the double helix. This activity relieves torsional stress that arises during replication and transcription. Because of its central role in DNA metabolism, human topoisomerase I is an established target for anticancer agents such as camptothecin derivatives.

How is human Topoisomerase I produced?
Our recombinant human Topoisomerase I is expressed in baculovirus-infected insect cells (Spodoptera frugiperda) and purified using methods adapted from Stewart et al., 1996. This expression system provides a reliable source of high-quality enzyme that closely mirrors native human activity.

What is the enzymatic activity of human Topo I?
One Unit of enzyme relaxes 0.5 µg of supercoiled pBR322 DNA in 1X assay buffer, in a 30 µl reaction volume at 37°C for 30 minutes. This precise definition supports reproducible results across experiments.

What is included with the enzyme?
The enzyme is supplied in dilution buffer together with 10X concentrated assay buffer. Additional assay and dilution buffer can also be ordered separately.

What are the main applications of human Topoisomerase I?
Typical uses include:

• Relaxation assays with supercoiled DNA substrates
• Mechanistic studies of DNA cleavage and re-ligation
• Screening of topoisomerase I inhibitors for cancer research
• Comparative studies with other topoisomerases

How should the enzyme be stored?
Store at –80°C for long-term stability. Avoid repeated freeze–thaw cycles. Bulk quantities and larger orders are available on request.

Do you provide quality control data and technical documents?
Yes. Each lot of human Topoisomerase I undergoes rigorous quality testing and is supplied with detailed technical documentation, including lot-specific activity data.

References

1. Stewart, L., Ireton, G.C., Parker, L.H., Madden, K.R. and Champoux, J.J. (1996). Biochemical and biophysical analyses of recombinant forms of human topoisomerase I. J. Biol. Chem. 271: 7593-7601