Figure 4.

Subcellular distribution of intracellular compartments in density gradients prepared from eosinophils. Guinea-pig eosinophils (5×10⁷), control unstimulated (a) or PMA-stimulated (500 ng/ml) for 8 min at 37° (b), were fractionated and eosinophil peroxidase (crystalloid granules), β-hexosaminidase (secretory/small granules and lysosomes), APDE (plasma membrane) and LDH activities were measured to determine positions of intracellular compartments in the gradient. (c) SOD-inhibitable superoxide-generating activity in fractions from PMA-stimulated cells. In (c), all fractions were measured in the absence of SOD (○) while fraction eight was additionally incubated in the presence of SOD (•). The specific activity of the peak superoxide-generating fraction was 890·3 nmol superoxide/min/mg of membrane protein. Activities from marker enzyme assays are depicted as percentages of maximal activity for the respective assay in fractions from the gradient. Fraction 1 contains 0% Nycodenz while fraction 16 contains 45% Nycodenz. These results are representative of three separate experiments.