Figure 6. Lysosomal enzyme activities of A2E-treated ARPE-19 cells challenged with rod outer segments. A: Cathepsin D activity of the ARPE-19 lysosomal fraction prepared from control and multiple 1 µM A2E-treated cells fed with rod outer segments (ROSs). Enzyme activity was measured with the Sensolyte 390 kit (n = 4 for each experimental condition). B: Acid phosphatase activity of the ARPE-19 lysosomal fraction prepared from control and multiple 1 µM A2E-treated cells fed with ROSs. Enzyme activity was measured with the standard p-nitrophenyl phosphate (PNPP) assay (n = 4 for each experimental condition).