Purity of essence
| 27 September, 2011 | Richard P. Grant |
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Last Friday we highlighted an evaluation of a paper reporting that a lot of papers might need to be scrutinized because they used a reagent–catalase–from a particular supplier. The catalase was contaminated with a compound that affected the very thing being measured (vasodilation in the kidney).
Via the magic of Twitter, we’ve learned that there might be problems with other Sigma enzymes too. Petra de Graaf, in Marc Timmers’ group in Utrecht, says that her lab bought MNase, a nuclease that is supposed to only digest single-stranded nucleic acids, from Sigma–and at least one batch of the enzyme also degraded proteins in their chromatin preparations. Not good. They subsequently switched to a competitor’s enzyme (MBI Fermentas) and haven’t, apparently, had further trouble.
That’s all well and good, but as the experiment was never published, how do other scientists get to know about it? Standing in front of a poster at a conference, and being asked “Where do you get your X from?”, then being told you should get it from somewhere else, is one way.
That seems a bit inefficient. Like negative results, there should be a more formal way of sharing such information, don’t you think?
It’s too important to leave to chance–or Twitter.
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There can be composition and purity issues with small-molecule reagents too. Unfortunately we can’t go back to the good old days when everything critical was quality-controlled. Of course this is still obligatory for bought-in pharmaceutical ingredients.
Pharmaceutical analytical reagents aren’t usually quality-controlled, and this can lead to trouble from time to time. From experience I found it best to choose when available a grade that has a specification for some specific application, even if this had nothing to do with my own. One example (writing from memory) was SDS, where you’d choose Fluka, not Sigma or Aldrich; they all belong to Sigma-Aldrich, but specifications are presumably one reason why the catalogues have been kept separate.
Yes, it’s been a while but I fondly remember the Aldrich catalogue–same stuff as Sigma, but better specs.
We used to make our own Pfu and stuff. People wondered about contamination, but really, it was the same as what you’d buy from the manufacturer. Just we weren’t automated and we couldn’t do analysis.