What is the relationship between specific activity units and International Units of activity?
There is no direct correlation or calculation between specific activity unit and International Unit (IU) values. International Units (IU) express a quantification of activity for the base amount of a substance in relation to an analogous reference standard with an internationally accepted unit of biological potency (i.e., IU/ng) that has been assigned based on an International Collaborative Study conducted by the World Health Organization (WHO). WHO Reference Standards are made available by the National Institute for Biological Standards and Control (NIBSC). Intended to simplify the comparison of activity of a substance obtained from different sources, IU measurements can vary as comparison methods are rarely the same between sources. A true direct comparison requires standardized methods of analysis in order to guarantee comparability of the substance’s activity in relation to its mass across sources.
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Why can't I see the protein pellet in the vial for my lyophilized recombinant protein? Is this normal?
Gibco recombinant proteins are frequently formulated without carrier proteins or additives (e.g., BSA, HSA, sucrose, etc.) and Gibco PeproTech recombinant proteins don't contain a carrier protein. As a result, during lyophilization, the protein product may be deposited on the vial as a thin, and sometimes invisible film instead of a pellet. The size of the pellet, if any, is not directly related to the quantity of the recombinant protein in the vial. Our quality control procedures assure that each vial contains the correct amount of product.
To ensure complete recovery of protein product, before opening a vial of lyophilized recombinant protein, we recommend centrifuging it in a microcentrifuge for 20-30 seconds to drive any protein that may be lodged in the cap or on the side or the bottom of the vial. After reconstitution, you can confirm the presence of product protein by running a small amount on SDS-PAGE. In general, a protein band with expected size should be visible with as little as 10 ng of protein loaded on an acrylamide gel.
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Does a particular recombinant protein contain the wild-type or mutated amino acid sequence?
Protein sequence information is available on the individual product page, except for proprietary engineered proteins.
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What kind of tubes should I use for storing aliquots of reconstituted recombinant proteins?
In general, we recommend using polypropylene tubes for storing aliquots of reconstituted recombinant proteins. Specific information for appropriate storage and handling of many recombinant proteins can be found on the product pages.
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Does each lot of recombinant protein have the same specific activity?
No, each lot can vary slightly with regards to its specific activity. The information on the data sheet for each product is provided as a guide. For lot-specific information, please please check the Certificate of Analysis or contact Technical Support.
