Frozen restriction enzymes

Dr. Duncan Clark duncan at
Fri Oct 18 09:56:25 EST 1996

In article <goldberg-1810960827320001 at>, Steven Goldberg
<goldberg at> writes
>I clean out my -20oC freezer every year and put the restriction enzymes at
>-80oC or on dry ice.  So far I have not noticed any that lose their
>activity after thawing at -20oC.

One thing to beware of which came as a big shock is that it appears that
CO2 gas can get past the o-ring seals in screw top eppendorf tubes even
if the lids are tight. We only found this out because we had some enzyme
in a storage buffer that contained a pH sensitive coloured dye. Storage
in a box with dry ice caused a pH shift from around 8 down to 7 where
the buffer was 20m Tris. We assume that very weak carbonic acid was
formed in the 50% glycerol storage buffer. Our best guess is that the o-
rings contract just slightly more than the plastic the vials are made
of. So far we haven't found a solution to this. Our vials are from
Sarstedt. We are now very wary about putting certain enzymes for
shipping in dry ice. Now they wil go on wet ice. 


My mind's made up. Don't confuse me with the facts!
Duncan Clark
DNAmp Ltd.

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