A product of proteolytic digestion of the DNA polymerase I from E. coli; it has both polymerase and 3´-exonuclease activities but not 5´-exonuclease activity. A dissociation constant that characterizes the binding of an enzyme to a substrate. The smaller the value of K, the tighter the binding of the enzyme to the substrate. Also called the Michaelis constant.
The Klenow fragment is a large protein fragment which is produced when DNA polymerase I from E. coli is cleaved by the protease enzyme subtilisin. It exhibits the 5’ → 3’ polymerase activity and the 3’ → 5’ exonuclease activity for removal of precoding nucleotides, but does not retain the 5' → 3' exonuclease activity.