Oxygen‐Dependent Cleavage of the Vinyl‐Ether Linkage of Plasmalogen

The vinyl‐ether linkage of plasmalogen was cleaved by rat brain homogenates; practically all activity was localized in the soluble fraction of the homogenate. The cleavage of the vinyl‐ether linkage was tightly coupled to the reduction of molecular oxygen; about 3.5–4 mol oxygen were reduced for each mol vinyl‐ether cleaved. Both the reduction of oxygen and the cleavage of vinyl‐ether ceased if the reaction was run in an atmosphere of nitrogen or if antioxidants such as N,N‐diphenyl‐p‐phenylenediamine, butylated hydroxytoluene or Quercetin were used, in the presence of oxygen. Either reaction was also inhibited by the addition of the following chelators: EDTA, citrate, dipyridyl, desferal and o‐phenanthroline. A detergent such as sodium deoxycholate was required for optimal activity. The reaction (i.e., vinyl‐ether cleavage or oxygen uptake) was directly proportional to protein concentration and time and had an optimal pH at about 7.3. When reaction rates were plotted against substrate concentration, hyperbolic curves of the Michaelis‐Menten type were obtained. The active component of rat brain supernatant was dialyzable, was not inactivated when heated for 10 min at 100 °C and did not precipitate in a saturated ammonium sulfate solution. This suggests that cleavage of the vinyl‐ether linkage of plasmalogen is catalyzed by a thermostable, low‐molecular‐weight, non‐protein component of rat brain supernatant.