The enzymatically catalyzed release of choline from lecithin.

In a recent series of papers, Kates (7-9) has presented a wealth of information in regard to the breakdown of lecithin by plant enzymes. A part of the work has been concerned with the degradation of phosphatidylcholine by carrot chromoplasts. The initial impetus to investigations concerned with phospholipide hydrolyzing plant enzymes which release free choline came from Hanahan and Chaikoff. These workers initially postulated (4), and later demonstrated (5, 6), the presence of an enzyme in carrots and cabbage capable of releasing large amounts of choline and a phosphatidic acid-like substance from plant lecithins. In their work with carrots, and likewise with cabbage tissue, these investigators were greatly limited by the extreme sluggishness of their reaction system. Similar difficulties were experienced by Acker et al. (1) in their attempts to purify and study the reaction mechanics of the enzyme from carrots. In Kates’ laboratory (7) it was found that enzyme activity from several different plant sources was greatly enhanced if diethyl ether were present in the reacting system. Under such conditions, activity could be measured after a 10 to 15 minute period, as contrasted to previously reported incubation times ranging from several hours to days. Kates’ initial report (7) showing the activating effect of diethyl ether could be presumed to indicate that, given the proper conditions, the reaction would conform more closely to that expected from enzyme catalysis. The work reported here indicates conditions which suggest the ease with which the system might presumably operate in nature. Of a group of inorganic salts tested, several of which increased the rate of cleavage of phosphatidylcholine, calcium (as the chloride) was the most potent activator. A satisfactory system for the analysis of carrot phospholipase D activity is presented which with slight modifications presumably could be applied to the analysis of other