The enzymatic synthesis of plasmalogens.

Recent work (1) has established that plaamalogenic phosphatides resemble the conventional glycerophosphatides such as phosphatidylcholme (I) very closely in structure, except that one fatty acid ester linkage is replaced in the plasmalogens by an aldehydogenic bond, presumably that of an a,fi-unsaturated ether. The exact position of the aldehydogenic bond is not yet certain. It had been concluded by Rapport (2) that the aldehydogenic linkage in the choline-containing plssmalogen of beef heart is in the fl position, since the remaining fatty acid ester bond is readily cleaved by lecithinase A of snake venom, described by Hanahan (3) as specific for the a’ position. However, more recent evidence of Tattrie (4) strongly suggests that lecithinasc A is specific for fatty acids in the fl position. This would mean that the aldehydogenic bond of the choline plasmalogen (and probably other plasmalogens as well) is in the 0~’ position. The structural relationship between these compounds and the well known glyceryl ethers such as batyl and chimyl alcohols would then become much more understandable. Accordingly, the structure shown in II will be assigned here to the choline plasmalogen of beef heart, but in view of the somewhat unsettled nature of the evidence to date, including claiis that plasmalogens of both types may be present in nature, this assignment must be regarded as somewhat arbitrary. It is known that the enzymatic synthesis of phosphatidylcholine (I) involves a reaction between n-a ,j3diglyceride (III) and cytidine diphosphate choline (5). I f a similar pathway were to lead to the biosynthesis of choline plasmalogens, presumably the last step of such a sequence would be a reaction between cytidine diphosphate choline and a compound of structure IV, which is a n-a,fldiglyceride in which one ester linkage has been replaced by an a ,&unsaturated ether bond. Assignment of trivial names to compounds of Type IV is rather difficult. It is proposed in this paper to describe any glycerophosphatide or related lipid in which one fatty acid ester linkage has been replaced by an aldehydogenic ether bond as ‘ ‘plasmalogenic”. Thus II may be described as plasmalogenic phosphatidylcholine (or choline plasmalogen) and IV may be described as a plasmalogenic diglyceride. This usage is simple, avoids an exact definition of structure at a time when this is not known with complete certainty, and is justifiable historically (6). The slight possibility of confusion arising from the descrip-