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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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up vote 12 down vote accepted

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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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)! –  nico Dec 24 '11 at 18:18
    
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. –  leonardo Apr 19 '12 at 16:47
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Freeze-thaw cycles denature proteins through local pH change effects

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A little brief? :) –  Rory M Dec 25 '11 at 18:19
    
It does get the point across. –  bobthejoe Feb 3 '12 at 21:04
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