Further evidence on the structure of slow reacting substance of anaphylaxis (SRS-A).

Arachidonic acid stimulates the release of SRS-A from the peritoneal cavity of sensitized rats or from rat peritoneal cells incubated in vitro. When rat peritoneal cells are incubated in the presence of tritiated arachidonic acid, significant amounts of radioactivity migrate in parallel to bioactivity on purification with Amberlite XAD-8, DE-52, Silicic acid and Sephadex LH-20. Lipoxidase (E.C. 1.13.1.13 and E.C. 1.13.11.12) inactivates mouse, rat and human SRS-A in a concentration-dependent pattern. Following extensive purification, rat SRS-A is also inactivated by the 2 x crystalline suspension of lipoxidase. These findings suggest (a) that SRS-A is a metabolite of arachidonic acid and (b) because of the strict specificity of lipoxidase, that the SRS-A molecule contains a cis, cis-1, 4-pentadiene and a structure very close either to arachidonic acid, to linoleic acid or to linolenic acid.