Hallo,

I noticed something strange, I regularly check activity of my proteins and it seems to increase over the time...

It is purified protein in a 50% glycerol solution and stored at -20C. Everytime I need some protein I pipette it into a new tube so the original one doesn't get thawed. When I test the activity I always check the concentration before to make sure that I'm using all the time the same amount of protein.
The activity right after the purification was set to be 100% but today (after about a month of storage) it was between 150-220% ???

Any ideas ???

that is bizarre. the only things I can think of are

1) you have changed some other parameter in you assay (time, temprature, concentration, buffer, pH)

2) your pipetter is not calibrated correctly

3) or the time in the refrigerator has left you with a more active enzyme

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Rb