Recombinant protein activity is highly dependent on the assay performed due to the wide array of variables within a given experimental system. Reference standards provide an effective means of controlling these variables across assays to determine the relative protein activity. By testing the material in question alongside a reference standard, the specific activity of the protein relative to the reference material can be determined.

The specific activity is reported in units (U) or international units (IU) when the reference material is recognized as a World Health Organization (WHO) international standard. Converting to units allows for a comparison of protein activity across multiple vendors and to ensure a consistent level of activity in an experimental system over time.

BioLegend often tests our recombinant proteins against commercially available reference standards, including WHO International Reference Standards, when available. Reference standards were obtained from the National Institute for Biological Standards and Control (NIBSC), a WHO collaborating center. The specific activity of these proteins can be found in the link below.

Read more: Recombinant Protein Unit Conversion, Specific activity of recombinant proteins


RayBiotech has been providing high-quality protein products to the scientific community for over 15 years. In addition to our diverse catalog of native and recombinant proteins, we also offer a comprehensive Custom Recombinant Protein Service to help meet all your research needs. If you have any questions about Raybiotech’s custom recombinant protein service, contact

Expression and purification services of recombinant proteins

Since 2006, RayBiotech has provided Custom Protein Services to produce recombinant proteins based on a customer’s specifications. Our comprehensive service program covers every step of production, from gene cloning through protein purification. We can also perform downstream processing like protein desalting, lyophilization, vialing, and labelling. 

Service Features 

✔ Comprehensive. From gene synthesis to protein purification, and beyond (desalting, aliquoting, lyophilization, conjugation) 

✔ Fast Turnaround. 3 weeks for bacterial expression; 8 weeks for mammalian cell expression.

✔ Easily Scalable. Once the protein has been purified for the first time, we can scale up production to your specifications.

✔ High Purity. Typically, >95% purity as determined with SDS-PAGE.

✔ Affordable. 

Overexpressed Proteins in Cell Extract and Culture Supernatant 

RayBiotech offers overexpressed recombinant proteins in unpurified cell extracts and culture supernatants derived from bacterial or mammalian cells. Protein expression is verified by western blot.


ProSpec’s recombinant proteins are are commonly used to produce protein-based polymers for drug delivery, antibodies and enzymes for disease treatment, protein scaffolds for tissue engineering, as well for many other uses. Recombinant proteins are a new combination of genes that form DNA. Recombinant DNA technology allows for the production of wild type and modified human and mammalian proteins in bulk quantities. Recombinant proteins are made from cloned DNA sequences which usually encode an enzyme or protein with known function.

Recombinant proteins are made through genetic engineering, also called gene splicing or recombinant DNA technology. By putting human, animal or plant genes into the genetic material of bacteria, mammalian or yeast cells, these microorganisms can be used as factories or producers to make proteins for medical, academic and research uses.

If you have any questions about ProSpec’s recombinant proteins and its size options, contact

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