Cellular depression of freezing point. Help!!

Ken Muldrew kmuldrew at acs.ucalgary.ca
Wed Nov 8 14:53:48 EST 1995

richwill at innotts.co.uk (richard williamson) wrote:

>Can anyone point me in the direction of information about what chemicals 
>some animals use to depress cellular freezing point?

Among mammals, I'm not aware of any freeze tolerance.  There are some
ground squirrels in Alaska who walk the tenuous path of being
supercooled for a week or two at a time during hibernation, but this
seems to be restricted to areas of deep permafrost.  Among terrestrial
animals, freeze tolerance is most common in insects, reptiles and
amphibians.  Tree frogs are probably the best studied and they seem to
use either glucose or glycerol as their principle cryoprotectant.
They are limited, however, as to what conditions they survive, with
death occuring in most terrestrial freeze tolerant animals when
greater than 65% of their body water freezes.  Insects have a greater
variety of strategies for freeze tolerance, some of which involve
vitrification--where their body water becomes a glass at low
temperatures--thus avoiding the limitations noted above.  An
interesting strategy employed by some arctic fishes which live in
water that is below the freezing point of their blood is to employ
antifreeze proteins.  These are small, helical proteins which bind to
the prism face of an ice crystal thereby increasing the energy
required for that crystal to continue growing.  Although these
proteins do not change the melting point of this ice, the temperature
at which crystal growth occurs is lowered so that any crystals in the
blood remain microscopic.  

Ken Muldrew
kmuldrew at acs.ucalgary.ca

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