The enzyme of this exercise could have increased its activity after their isolation, due to an increase in the substrate this enzyme acts on. For example, after we eat our food at dinner, the concentration of our bodies' insulin increase, due to a higher concentration of glucose from that aliments provenience from the digestion on our stomachs. This also can cause a positive feedback reaction in our bodies, which means that a little amount of enzyme, can produce more of this molecule, and they are those kinds of metabolic processes which usually are involved in maintaining our bodies' homeostasis.
We can see an example of this in the following picture, where the presence of a substrate, activates the enzyme.
