Re: what would happen if enzymes are mixed with liquid nitrogen

Dear James,

Thanks for your question. I agree, liquid nitrogen is pretty cool stuff. Here is some information about liquid nitrogen. Unlike water, which turns from gas (steam) to liquid below 100 °C at 1 atmosphere, nitrogen doesn't become liquid until below -196 °C. This is so cold that if you put objects into liquid nitrogen, they instantly freeze solid and become very brittle. Try this Google video search to see some liquid nitrogen experiments. Look for the one where a flower is frozen in liquid nitrogen - the flower can be smashed like glass!

So, what happens to enzymes in liquid nitrogen? Well, first you need to know that enzymes are molecules. In fact they are quite large molecules - still too tiny for us to see but bigger than most other molecules. Enzymes are proteins and protein molecules are chains made from smaller units (called amino acids). Most enzymes will dissolve in water, because the amino acids carry charge - either positive or negative - and so do the water molecules. So instead of sticking to each other, the enzyme molecules separate from each other and dissolve in the water. We say that water is a good solvent - a lot of things like to dissolve in it.

It's very difficult to study what happens when you add things to liquid nitrogen, because it boils away (turns to gas) very easily when you add things to it. However, we know that nitrogen molecules are not charged in the same way as water molecules and so liquid nitrogen is not a very good solvent. So if you added solid enzyme (as a powder) to liquid nitrogen, it would not dissolve - the powder would just stick together and sink to the bottom. If you added a solution of enzyme, with the enzymes dissolved in water, the water would just instantly freeze solid, trapping the enzymes inside water ice crystals.

Enzymes can be cooled in liquid nitrogen and they will still work when you thaw them out. In fact you can freeze whole cells (which are full of many types of enzyme), then thaw them out and bring them back to life. Note though that when we say "frozen in liquid nitrogen", the liquid nitrogen does not come into direct contact with the object which is frozen. The object would be placed in a small, sealed plastic tube, called a cryovial, which is then suspended in the liquid.