Acid and Neutral Sphingomyelinase Activity in Azurophil and Specific Granules and in Plasma Membranes in the Presence or Absence of Dithiothreitol or Hg2+
| . | Sphingomyelinase Activity . | |||||
|---|---|---|---|---|---|---|
| Control . | Dithiothrietol . | Hg2+ . | ||||
| A . | N . | A . | N . | A . | N . | |
| Azurophil granules | 0.15 | 0.58 | 0 | 0.7 | 0.76 | 0 |
| Specific/gelatinase granules | 0.2 | 5.1 | 0 | 5.7 | 0.3 | 0 |
| Membranes | 0.25 | 93.4 | 0.34 | 107.8 | 0 | 0 |
| . | Sphingomyelinase Activity . | |||||
|---|---|---|---|---|---|---|
| Control . | Dithiothrietol . | Hg2+ . | ||||
| A . | N . | A . | N . | A . | N . | |
| Azurophil granules | 0.15 | 0.58 | 0 | 0.7 | 0.76 | 0 |
| Specific/gelatinase granules | 0.2 | 5.1 | 0 | 5.7 | 0.3 | 0 |
| Membranes | 0.25 | 93.4 | 0.34 | 107.8 | 0 | 0 |
PMNs were fractionated on two-layer gradients as described, and azurophil granules, specific/gelatinase granules, and light membranes obtained by aspiration with a pipette. Percoll was removed by ultracentrifugation and the biological material resuspended in PBS. Assays for acid (A) and neutral (N) sphingomyelinase were performed as described in the presence or absence of 0.05 mmol/L HgCl2and 1 mmol/L dithiothreitol, respectively. Activity is expressed in pmol sphingomyelin hydrolyzed/min/mL. Data from one representative experiment are shown.