An interesting observation noted while doing our experiments lead us to look at individual growth characteristics of cells over-expressing each of the oxidative repair enzymes. Cells over-expressing the repair enzyme hMYH clearly grow at a slower rate when compared with the other enzymes. The mechanism behind this is not understood at this point in time. The repair action of Cell growth curve and associated doubling times (DT) Figure 6 Cell growth curve and associated doubling times (DT hMYH is known to remove adenines misincorporated opposite 8-oxoG lesions. This lesion occurs when a C/GO lesion is allowed to replicate before being corrected by hOgg1. Repair by hMYH is not a final corrective measure. The product of hMYH activity is the lesion C/GO, which allows hOgg1 to have another opportunity to remove 8-oxoG opposite cytosine. We know that A549 cells possess the hOgg1 gene based on a previous study demonstrating the presence of this gene after amplification by genomic PCR [45] . We also have demonstrated endogenous activity of hOgg1 in A549 cells by using an 8-oxoguanine bioactivity assay. Therefore, our explanation of these results is that the slowed growth created by hMYH may provide a wider window of opportunity for the repair process to take place, which ultimately grants endogenous hOgg1 another opportunity to remove the 8-oxoG lesion created by oxidative stress.