Metabolism in frozen tissue - Is there any? (Mar/04/2009 )

One of my colleagues insists that in tissue fragments frozen in 10% DMSO in liquid nitrogen vapour phase there will be some metabolism, albeit very slow.

I find this hard to believe. Surely everything should have stopped at that temperature.

Tried Google, but couldn't find much.

Does anyone have any thoughts on this?

Cheers
Chris

I would guess there would be no metabolism. If there was, all the cells we freeze would be killed by the DMSO.

According to quantum theory, there is always molecular movement above 0 Kelvin, so, in theory there could still be metabolism happening at LN₂ temperature. However, as cells are largely composed of water with a few salts and other substances thrown in, at liquid nitrogen temperatures, the water is mostly frozen in the form of crystals, thereby preventing movement of large molecules. Whether or not this actually completely prevents metabolism is up for debate, as there should always be some free water around.

As far as I'm aware, the lowest anyone has recorded enzymatic activity is c.a. -100oC using thermophilic enzymes in MeOH solutions and recording the activity over several months.
I guess it depends on what the definition of metabolism is.

DRT on Mar 4 2009, 05:05 PM said:

Thermophilic? Heat loving enzymes at -100?

bob1 on Mar 6 2009, 10:51 AM said:

Mainly so that they can withstand the high methanol concentrations needed to keep a liquid(ish) environment; but also one of the side affects of thermostability is a decrease in the cold-denaturation temperature (at least theoretically, on the basis of the free energy curves).

Fair enough, sounds reasonable to me.