. 2010 Aug 17;5(8):e12241. doi: 10.1371/journal.pone.0012241

Table 1. Steady state kinetic parameters of the WT and mutant APE1 proteins.

	APE1 WT		APE1 K98A/R185A		APE1 R185A		APE1 K98A		APE1 D308A		APE1WT	Fold decrease of k _cat/K _M value of APE1 mutants compared to WT
	K _M, nM	k _cat, min⁻¹	K _M, nM	k _cat, min⁻¹	K _M, nM	k _cat, min⁻¹	K _M, nM	k _cat, min⁻¹	K _M, nM	k _cat, min⁻¹	k _cat/K _M, min⁻¹·M⁻⁶	K98A/R185A	R185A	K98A	D308A
THF•T ^a	0.87	15	8.3	3.2	4.7	4.7	2.4	38	0.4	6.6	17200	44	17	1.1	1.1
THF•T ^b	0.27	0.46	3.0	0.36	2.0	0.09	1.9	0.25	0.31	0.35	1700	14	38	13	1.5
αdA•T	0.27	0.31	NONE	NONE	7.4	0.038	4.8	0.1	NONE	NONE	1100	∞	220	52	∞
DHU•G	780	13	NONE	NONE	220	0.2	360	5.4	23	0.093	16	∞	18	1.1	4.1
Exo20^THF•G	8.2	6.4	27	0.24	5.3	2.4	15	8.4	5.4	0.56	780	87	1.7	1.4	7.5
Exo20^P•G	20	3.6	3.8	0.38	3.2	0.7	7.3	2.2	N.D.	N.D.	180	1.8	0.8	0.6	N.D.
Exo20•G	2.4	0.86	NONE	NONE	5.7	0.1	6.1	0.14	21	0.027	360	∞	20	16	280

Each type of DNA substrates was used to measure a specific APE1 activity under appropriate optimal reaction conditions: THF•T for AP endonuclease activity; αdA•T and DHU•G for NIR activity; Exo20^THF•G for 3′-repair diesterase activity; Exo20^P•G for 3′-phosphatase activity and Exo20•G for 3′→5′ exonuclease activity (see Methods ). To determine K _M and k _cat, the linear velocity was measured and the constants were calculated using Lineweaver-Burk plots. Standard deviations for K _M and k _cat values varied within 20–40%. NONE = no activity was detected under these experimental conditions, N.D. = not determined.

Standard AP endonuclease reaction conditions were used for AP endonuclease assay.

NIR reaction conditions were used for AP endonuclease assay.