Investigating protein purity is a tricky though valuable question. The reason why it is tricky is that there are many different ways at looking at a biological sample to see what may have gone wrong e.g…

Have my proteins been post-translationally modified (e.g. oxidised)?
If so, do the post translational modifications change activity (many methionine oxidations don’t effect activity)?
Have my proteins been cleaved?
Have my proteins precipitated out of solution?
Have my proteins aggregated into a suspension?
Have additional proteins been added to the solution?
Have a subset of my proteins been effected dis-proportionally to the others?
Has the buffer composition been changed?
If so do the changes to my buffer composition affect activity?

Overall the questions tend to group around:

Has my sample been changed in a way that affect the activity I want?
Has my sample been changed in a way that introduces activity I don’t want?

If your standard is a natural product and therefore unlikely to have ever been 100% pure. Purity is often defined by the tests performed and we have identified 100’s of proteins in commercial ‘pure’ standards in the past. This is not necessarily an issue as it has to be fit for purpose – impure standards can be fine unless there is some nasty side activity in there that messes things up. Quality control is very important but you need to be aware that you may not get a simple answer and any statement you make may need to be qualified and justified.

The services we can offer include protein composition analysis, post-translational modifications analysis and intact mass determination but you may also want to consider the services of the Biomolecular Analysis Core facility that can provide support with biophysical analysis including looking at aggregation and concentration analysis as well as providing support for formulation testing too.

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