12.5.1 Phospholipase A 1
Although several reports exist on hydrolysis reactions catalyzed by PLA 1 (Fauvel et
al., 1984; Kucera et al., 1988; Mustranta et al., 1994; 1995), the enzyme has not yet
obtained marked significance in enzymatic syntheses. One reason for this is the
instability of the hydrolysis products. 1-Lysophosphatides formed by PLA 1 are sub-
jected to rapid acyl transfer, yielding the more stable 2-lysophospholipids, and there-
fore are not of great practical interest. The second reason is that transesterification of
phospholipids is accomplished also by several lipases, e.g. fromRhizopus delemar
(Brockerhoff et al., 1974),Rhizopus delemar(Haas et al., 1993),Mucor javanicus
(Morimoto et al., 1993), which are better available and more thoroughly investi-
gated.
12.5.2 Phospholipase A 2
Secretory PLA 2 s, mainly from pancreatic sources, are well-known as industrial cat-
alysts in the production of 2-lysophospholipids from natural or synthetic PC (refer-
ences in Mustranta et al., 1994). Lysophospholipids are important emulsifiers in the
food and pharmaceutical industries. In recent years increasing efforts have been
made to use PLA 2 for reacylation or transacylation of phospholipids in thesn- 2
position (Figure 10 and Table 2). In fact, reacylation was found more successful
than transacylation. Yields of acylation products starting from lyso-PC have been
improved from 7 % in early reports (Pernas et al., 1990) to 60 % in the more recent
study by Egger et al. (1997), in which success was based on careful control of water
activity in the reaction mixture.
Application of PLA 2 has been envisaged also in medicine. In the treatment of
hypercholesterolemia, an extracorporeal shunt system was designed which con-
12.5 Examples of application 239
Figure 10. Modification of phospholipids by PLA 2. (A) Introduction of fatty acids into lyso-glycero-
phospholipids. (B) Exchange of fatty acids in glycerophospholipids.