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We all know restriction enzymes are proteins, but we never freeze them. They are instead provided in high glycerol containing solutions by companies and stored at -20C. Is there a reason why this is so?

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It's just so much more convenient to have the enzymes ready without having to thaw them. The main reason you freeze enzymes is to keep them active, if you figure out a buffer that keeps them unfrozen without compromising activity, that is a huge increase in convenience.

Not having to thaw the enzymes before use saves a lot of time, if you can manage to keep the enzymes active in those non-freezing conditions that is a clear advantage.

Glycerol also stabilizes proteins in solution, and multiple freeze and thaw cycles can negatively affect enzyme activity for some enzymes.

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    $\begingroup$ Just as an addition: you can do the same with antibodies. On reception, dilute them 1:2 in glycerol and you can avoid aliquoting them and don't have to worry about freezing cycles (remember to double the amount when you use them, though)! $\endgroup$
    – nico
    Dec 24, 2011 at 18:18
  • $\begingroup$ Glycerol is added as an anti-freeze agent as well, so that the enzyme can be kept at low temperature (low kinetic energy) and therefore stay stable for longer periods of time. $\endgroup$
    – user560
    Apr 19, 2012 at 16:47
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Freeze-thaw cycles denature proteins through local pH change effects

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    $\begingroup$ A little brief? :) $\endgroup$
    – Rory M
    Dec 25, 2011 at 18:19
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    $\begingroup$ It does get the point across. $\endgroup$
    – bobthejoe
    Feb 3, 2012 at 21:04

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