Figure 3.

Proteasome activity is reduced in senescent WI-38 cells. (A) Cell lysates were prepared from proliferating or senescent WI-38 cells. Protein concentrations were normalized and proteasome activity was determined using a synthetic fluorogenic substrate (± standard error; n = 4). The reduction in proteasome activity was found to be significant in the older cells (**, p < 0.01). (B) Polyubiquitinated proteins found in the cytosolic extracts of proliferating and senescent WI-38 cells. Sample concentrations were normalized and the level of polyubiquitin-protein conjugates was determined by immunoblot using an antibody specific for ubiquitin.

Place et al. BMC Cell Biology 2005 6:37   doi:10.1186/1471-2121-6-37
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