The site of action of lecithinase A of lecithin.

The site of action of lecithinase A, which removes a single fatty acid from a glycerophospholipide molecule, has never been proved. The only report known to the author on this subject was that of Levene and Mehltretter (l), who were unsuccessful in their attempts to make a derivative of lysolecithin which had been prepared by the action of snake venom on egg lecithin. The availability of pure, homogeneous lysolecithins (monopalmitoleyland monopalmitoyllecithin), which were produced enzymatically by the action of Naia naia venom, Crotalus adamanfeus venom, or pancreatin extracts (2) on the corresponding a-lecithin, made possible a detailed study of the position of the free alcohol group in these compounds. Several promising lines of attack on this problem were available. Foremost among these possibilities was that of the acylation of the alcohol group. However, under‘a variety of conditions in different solvents, no reaction of the lysolecithin could be effected with reagents such as stearoyl chloride, palmitoyl chloride, p-nitrobenzoyl chloride, phthalic anhydride, or acetic anhydride. In addition, the preparation of the a-naphthylor 3nitronaphthylurethane was unsuccessful. Another possible approach was to remove enzymatically the phosphorylcholine from the lysolecithin by the use of lecithinase D with the resultant production of an easily identifiable monoglyceride. However, in confirmation of the indirect evidence obtained by Zamecnik et al. (3) on the inactivity of lecithinase D towards lysolecithin, no action of this enzyme on pure lysolecithin could be elicited. It was hoped that migration of the acyl group of the lysolecithin could be effected with conditions under which it is well known that the /?-acyl group of fl-monoglycerides or (Y, p-diglycerides will migrate quantitatively to the or position (4). When lysolecithin was incubated in alcoholic 0.06 N HCl for 36 hours at room temperature and the optical activity of the solution measured at frequent intervals, no change was noted. If any migration had occurred, it seemed most likely that a change in rotation would have resulted. It is possible that the acyl group was already on the a: position or that it was on the P-carbon, and that its migration was hindered by a cyclic phosphate structure involving the free alcohol and the phosphate groups or by hydrogen bonding between the free alcohol and the fatty acid ester. It