12.5.4 Phospholipase D
PLD has been the most used phospholipase hitherto, mainly due to its relatively
strong propensity to catalyze transesterification at the terminal phosphate ester
bond of phospholipids. This transphosphatidylation is in competition to hydrolysis
(Figure 12), but in contrast to transesterification reactions by other types of phos-
pholipases, some PLDs favor transphosphatidylation over hydrolysis and allow the
synthesis of new phospholipids in high yield. The syntheses of diacylglycerophos-
pholipids by PLD are reviewed in Table 3, while selected structural formulae of head
groups introduced are shown in Figure 13. PG, PS or PE are also known to be pro-
duced by transphosphatidylation with PLD in industrial scale. While in earlier re-
ports PLD from cabbage was mostly used, more recently PLDs fromStreptomyces
strains have been preferred for synthetic purposes (Table 3). The observed transphos-
phatidylation activities are very different where – according to the kinetic particu-
larities of PLDs described in Section 12.4 – the source of the enzyme, the reaction
media and the acceptor alcohols seem to be interdependent, and the derivation of
general rules is difficult. In fact, PLDs from someStreptomycesstrains seem to
be predestined for transesterification of glycerophospholipids whereas PLDs
from other strains, e.g., fromStreptomyces chromofuscusfail in this function.
PLD from cabbage has an intermediate position in this series. Water and alcohol
strongly compete for the phosphatidyl moiety, and the formation of phosphatidic
acid has to be tolerated in most reactions.
While all conversions listed in Table 3 start with natural or synthetic PC, Table 4
summarizes PLD-catalyzed transesterification of compounds not containing the dia-
cylglycerol backbone. These examples show that alkyl moieties attached to glycerol
by an ether bond, as well as 3-fold unsaturated fatty acids in the substrate molecule,
are accepted. Interestingly, even alkylphosphocholines lacking the glycerol back-
246 12 Phospholipases Used in Lipid Transformations
Figure 12. Hydrolysis and transphosphatidylation of glycerophospholipids by PLD. X 2 OH: acceptor
alcohol