pases which are selective for the 1- and 3-positions in triglycerides are selective for
thesn-1 position of glycerophospholipids. As several cheap (mostly of microbial
origin), easy-to-handle lipases are available, they constitute a practical synthetic
tool. The hydrolysis of phosphatidylcholine can be carried out in aqueous solu-
tion, the reaction rate being improved by the addition of a surfactant such as Triton
X-100 (Morimoto et al., 1993) so that mixed micelles are formed. In order to obtain
the 2-acyl lysophosphatidylcholine in a pure form it was necessary to use a boric
acid-borax buffer to suppress acyl migration.
The hydrolysis of glycerophospholipids can also be carried out in organic solvents.
ImmobilizedRhizomucor mieheilipase (Lipozyme) was used to catalyze the hydro-
lysis of phosphatidylcholine in different organic solvents (Haas et al., 1993), the best
results being obtained in relatively polar solvents such as butanone.
Quantitative removal of the fatty acid in thesn-1 position has been reported using
lipases fromRhizomucororRhizopusin a microemulsion (Hara et al., 1997). To
prepare the microemulsion, Aerosol OT (the sodium salt of dioctylsulfosucci-
nate) was used as surfactant and isooctane as organic phase. Microemulsions using
the same components were used as the reaction medium to remove the fatty acid in
thesn-2 position of phosphatidylcholine using porcine pancreatic phospholipase A 2
(Morgado et al., 1995). Almost 100 % conversion was achieved in 10 min. It should
be noted that during hydrolysis in microemulsions, phosphatidylcholine acts both as
a substrate and as a surfactant active in the formation of the microemulsion. As the
reaction proceeds, phosphatidylcholine is converted to lysophosphatidylcholine, and
so the behavior of the microemulsion may change, especially if high substrate con-
centrations are used.
The phospholipase A 2 -catalyzed hydrolysis of phospholipids is used in industrial
processes. For example, in the processing of vegetable oils it is important to remove
the phospholipids from the oil. As it is easier to remove lysophospholipids than fully
acylated phospholipids, it is worthwhile carrying out a phospholipase A 2 -catalyzed
hydrolysis (Buchold, 1993), the lysophospholipids being extracted into an aqueous
phase after the reaction has been completed.
296 14 Enzymatic Conversions of Glycerophospholipids
Figure 5. Non-selective or regioselective removal of fatty acids from glycerophospholipids. The reac-
tions used can be either hydrolysis or alcoholysis reactions.