Front Matter

tion. Some lysophospholipid must be formed (see Figure 3), but in the final product

there should not be too much of this material. Compared to reactions involving fatty

acid exchange in triacylglycerols, the equilibria are much less favorable for glycero-

phospholipids. Thus, under similar conditions (water activity, fatty acid concentra-

tion, etc.) the product mixture contains much more partially deacylated compounds

in the case of phospholipids than in the case of triacylglycerols. Different reaction

systems containing only low amounts of water have been evaluated for this kind of

reactions (Adlercreutz, 1994). Immobilization of the lipase on a porous support and

suspending this enzyme preparation in the reaction mixture has been used success-

fully in a number of studies. UsingRhizopus arrhizuslipase immobilized on poly-

propylene as catalyst and toluene as solvent, a yield of 60 % of modified phospha-

tidylcholine was obtained when the water activity was controlled at a low level of

0.11 (Svensson et al., 1992). In this case, virtually complete exchange of the fatty

acid in thesn-1 position was achieved.

In the incorporation of extra eicosapentaenoic and docosahexaenoic acids (EPA

and DHA) into fish oil, it was found useful to carry out the reaction in a mixture of the

reactants with just a small addition of a polar solvent, such as formamide, ethylene

glycol or propylene glycol. The function of the polar solvent was to act as a ‘water

mimic’ and thus activate the enzyme while still maintaining a low water activity in

the reaction mixture (Hosokawa et al., 1995b).

14.7 One-step exchange of fatty acids using

phospholipase A 2 as catalyst

In the reactions catalyzed by pancreatic phospholipase A 2 , no acyl-enzyme is

formed, and therefore transesterification reactions according to Figure 3 are not

possible. On the other hand, if reaction conditions can be found under which

both hydrolysis and esterification occur simultaneously, fatty acids can be ex-

changed in an one-step process. In order to obtain a good yield of the fully acylated

lipid, it is necessary to use a relatively low water activity, or the equilibrium mixture

will contain too much lysolipid. A one-step fatty acid exchange in glycerophospho-

lipids has been carried out using pancreatic phospholipase A 2 as catalyst (Hosokawa

et al., 1998), an incorporation of 35 % of polyunsaturated fatty acids and a yield of

18 % being achieved using glycerol with low water content as solvent (Hosokawa et

al., 1998).

14.8 Reactions catalyzed by phospholipase C and D

Phospholipase C has been used to a relatively low degree for synthetic purposes. In

the reported applications, the enzyme has been used to catalyze hydrolysis; starting

from natural glycerophospholipids, the hydrolysis products were chiral diacylglycer-

ol and phosphorylated alcohols, which may be of considerable interest (Anthonsen et

al., 1999).

14.8 Reactions catalyzed by phospholipase C and D 303