Analysis of z-EK(bio)D-aomk-labeled caspases by two-dimensional gel electrophoresis. (A) Analysis of active caspases in HL-60 cytosol (left) and nuclei (middle). The spots are indexed as recently described.38 In these gels, the pH decreases from left to right. This analysis showed a novel active species (D) in HL-60 nuclei. The merged picture (right) was obtained by co-electophoresing mixtures of, respectively, HL-60 cytoplasm + active caspase-2 and HL-60 nuclei + active caspase-2 (data not shown). Caspase-2, which was previously shown not to comigrate with any of the caspases detected in HL-60 cytosol,38 provided a reference point for alignment of the cytosolic and nuclear images. Arrows in the merged image point to species observed in the nuclear fractions. (B) Analysis of active caspases in K562 cytosol (left) and nuclei (middle). Images were merged (right) as described for (A). (C) Comparison of the pattern of active caspases in cytosol and nuclei of HL-60 and K562 cells. Crosses correspond to the exact positions of the active species in HL-60, and circles correspond to the exact positions of the active species in K562.