Table 2.

Sensitivity and reproducibility of DNA repair enzyme activity assays

Assay	Lower LoD (U/well)a	Amount of NE (ng/well)b	Intra-assay CV (%)c	Inter-assay CV (%)d
		1000	18 ± 3	18
UDG (U:A)e	0.009	2000	10 ± 2	10
		3000	8 ± 2	6
UDG (U:G)6	0.006	nd	nd	nd
		2	28 ± 11	8
AP site incision	0.005	4	14 ± 3	13
		8	12 ± 4	12
		12.5	12 ± 4	15
DNA polymerase	8 × 10−7	25	5 ± 1	9
		50	9 ± 3	6
		100	5 ± 1	6
DNA ligase	2 × 10−6	200	5 ± 2	10
		200	10 ± 4	20

^aLower limit of detection (LoD) calculated by interpolating enzyme activity for mean absorbance at 0U enzyme minus 2 × SD for uracil DNA glycosylase (UDG) and AP site incision assays, or mean absorbance at 0U enzyme plus 2 × SD for DNA polymerase and DNA ligase assays.

^bAmounts of nuclear extract (NE) used for determinations of assay coefficients of variation (CV).

^cMean ± SD of intra-assay CV based on four individual analyses each of eight technical replicates.

^dInter-assay CV calculated from assays performed on four independent plates.

^eSensitivity and reproducibility of UDG assay measuring excision of uracil from a substrate containing an U:A base pair.

^fSensitivity of UDG assay measuring excision of uracil from a substrate containing an U:G mismatch. A HepG2 NE quality control sample was used for all assay CV determinations with the exception of UDG, for which a Caco-2 NE quality control sample was used.