If possible companies would sell enzymes which are stable at room temperature. Because this is seldom the case they recommend storage at -20°C because you can find a -20°C freezer in every lab. I haven´t heard of an enzyme which will be degraded or inactivated by storage at lower temperatures. NEB e.g. sells enzyme which must by stored at -80°C. Usually the enzymes come in a storage buffer with glycerine or other stabilizers and it is safe to store them at -80°C.

Dear Kamesh:

It depends on the enzyme, but usually most of the can be stored for a long time at -80ºC using proper buffers (containing glycine, glycerine, glicerol, ectoine, etc.). Enzyme providers use to give protocols to storage the enzymes under these conditions.

Good luck!

Kamesh,

As others have stated it is 100% enzyme-dependent. Some enzymes can be stored for years at -80C without losing activity, whereas others will immediately lose activity when frozen.

Generally, anything that retains activity after being fully frozen at -20C will also remain active after being frozen at -80C. Either way they are frozen. In my experience flash-freezing (in liquid nitrogen) and storage at -80C works better as you can avoid some crystallization of water which could shear your enzyme of interest.

Reducing the temperature from -20 to -80 °C would harm those proteins that are stored in glycerol/water mixtures to prevent freezing. The lowest freezing point of glycerol/water mixtures is about -46 °C for 67% glycerol (DOI:10.1021/ie50189a017).

As Engelbert said, freezing enzymes that don't freeze because of their buffer mixture can always cause loss of activity. This is why I qualified my generalization with fully frozen at -20C. An important clarification!