Equal amounts of liver cytosolic proteins (40 μg/well) from different groups were separated on 12% SDS–PAGE, transferred to nitrocellulose membranes, and subjected to immunoblot analysis by using anti-ubiquitin (A and B, upper panels) and anti-β-actin antibody (A and B, middle panels) for normalization. Coomassie-stained gels are also presented (A and B, lower panels) to further demonstrate equal protein loading. The relative ratio of the 3-NT level detected between the APAP-exposed samples and the corresponding control, which was set at 1, is shown in the top.