TI - Kinetic constants of the human DNA repair proteins for the incision of duplex oligonucleotides containing a single modified residue . AB - Protein Substrate KM (nM) kcat ( min-1 ) kcat/KM ( min-1uM-1 ) Ape1a THF*G 19 + - 2.0 . 30 1600 Ape1b THF*G 2.7 + - 0.4 . 0.12 . 45 Ape1b alphaA*T 7.2 + - 1.6 . 0.12 . 16 Ape1b DHU*G 8.4 + - 1.8 . 0.16 . 19 hNth1c DHU*G 47 0.6 . 13 a , bEnzyme activity was measured under standard reaction conditions for AP endonucleasea or NIRb assay ( see Materials and Methods ) . cData taken from ( 50 ) .