for their products. However, APE1 appears to form very stable complexes with its product.^36 Thus, the
enzyme holds onto the product after cleavage, since severed DNA poses great risk to the cell, and then
delivers it to the next component of the repair machinery.
Certain repair enzymes cause the damaged nucleotide to be flipped outfrom the DNA double helix. In
such enzymes, the nucleotide is accommodated in a specific binding pocket within the enzyme.
10.5.3 DNA Glycosylases
Glycosylasesare enzymes that excise damaged DNA, as the first step towards repair. The enzyme uracil–DNA
glycosylase functions to remove the base wherever uracil bases occur in DNA as a result of either
406 Chapter 10
Figure 10.13 The structure of a representative repair enzyme, the human APE1 protein bound to DNA (PDB: 1DE8)