enzyme
A polypeptide or protein that acts as a catalyst for biochemical reactions. Enzymes do not actually cause a reaction to occur, but rather speed up the rate at which an ongoing reaction takes place. Virtually all signifi cant biochemical reactions in living systems are catalyzed by enzymes.
Klenow fragment,enzyme
A subfragment of DNA polymerase I produced by proteolytic cleavage of the 103 kD enzyme by subtilisin. The Klenow fragment is the larger (68 kD) of the two subfragments produced by subtilisin treatment. This fragment retains the normal DNA polymerase and 3′→5′ exonuclease activities but lacks the 5′→3′ exonuclease of the intact enzyme.