The Structure of Plasmalogens

In the previous paper (1) we described a sequence of events which led from the isolation of crystalline “acetal phospholipide” by Feulgen and Bersin, and the realization by Schmidt and coworkers that the properties of this compound differed from those of native plasmalogen, to the preparation of plasmalogen fractions in this laboratory which indicated the presence of a fatty acid ester residue in addition to the aldehydogenic chain. The inadequacy of the formulation of native plasmalogens as glyceryl acetals was first surmised by Anchel and Waelsch (2) from the enormous disparity between the rates of reaction with fuchsin-sulfurous acid reagent of synthetic glyceryl acetals and lipide extracts. They reported that their results “suggest that the aldehyde linkage in the naturally occurring complex may be more labile than the acetal linkage with glycerol.” A crucial observation with respect to the nature of this linkage was made by Klenk and Debuch (3, 4), and independently in this laboratory (5) ; namely, catalytic reduction leads to the complete disappearance of aldehydic reactions and the formation of a glyceryl ether. Klenk and Debuch (4) believe this property to be consistent with the hemiacetal structure (I), while our formulation of the linkage of the aldehydogenic chain favors the unsaturated ether (II). These observations were made with plasmalogen fractions containing a substantial quantity of non-aldehydogenic component, such as phosphatidylethanolamine or phosphatidylcholine. The only “pure” aldehydogenic phospholipide isolated is still that reported initially by Feulgen and Bersin (6) and later by Thannhauser, Boncoddo, and Schmidt (7), which presumably has the glyceryl acetal structure (III). The questions arise whether this compound is naturally present in tissues