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Answers to Common Questions About the Activity of Recombinant Proteins

As many of you may know, recombinant proteins are commonly used in research models to address cell function and behavior questions. However, it is not uncommon for researchers to be puzzled by what specific activity means and how ED50 and IU correlate.  Here we provide answers to some of the most common questions related to the activity of recombinant human il-2.

How is Activity Measured?

The activity of a recombinant protein is measured by conducting a bioassay. One of the most common ways to measure the activity of recombinant proteins is to see how they affect cell proliferation. Recombinant proteins’ biological activity can also be measured using enzyme assays and functional ELISAs. However, because there are numerous types of cells, one measurement will not work on all. Different cell types will respond differently when exposed to different recombinant proteins in a bioassay, which is why some cells need to be tested in different ways with different measurements.

What is an ED50?

To calculate a recombinant protein’s activity, you must first find the ED50. The term “ED50” stands for the Median Effective Dose and represents the dosage or concentration at which half of a population is expected to respond. In our case, it represents the concentration in ng/ml, at which recombinant human IL-2 will cause 50% of CTLL-2 cells in the bioassay to proliferate.  To determine ED50 values, you’ll need to plot a dose-response curve for the bioassay testing the activity of the recombinant protein on CTLL-2 cell proliferation.

However, the rule of thumb is that you can only use a bioassay to determine the ED50 if it produces a sigmoidal dose-response curve. For instance, the following graphs show how different concentrations of recombinant human IL-2 elicit different cellular responses on CTLL-2 cell lines.

Figure 1: Sigmoidal dose-response curve for IL-2 Cytotoxic activity on the CTLL-2 cell lines. Figure 2: Typical sigmoidal response curve for the measurement of IL-2 on activity on  HT-2 cell lines.

Are Bioactivity Units and International Units the Same?

The international unit (IU) is a unit of measurement for biological activity. It is often used to describe the potency of proteins and hormones. You can also apply IU’s to recombinant proteins. In contrast, Bioactivity Units (BU) measure the amount of bioactive material present in a sample that causes some effect on the cells being assessed by following a particular protocol or under specific conditions defined by an assay manufacturer or assay kit protocol.

Recombinant proteins are a powerful tool for research and can give us great insight into how cells work. To use them effectively, it is essential to understand the activity of recombinant proteins and determine their ED50. How do you measure bioactivity units or international units? The answers to these questions may help you better utilize your recombinant protein in future research endeavors with cell lines.  If this sounds interesting, our team is here to provide expert advice on the type of bioassay best suited for your specific needs. Let us know at https://www.shenandoah-bt.com/human-il-2.html if we can answer any more questions about the activity of recombinant proteins today!