Front Matter

solvent effects in hydrolysis and transphosphatidylation of PC by PLD from cabbage

andStreptomycesspp., postulated that the interfacial pressure being correlated with

the package density of the PC aggregates was the main regulator of enzyme activity.

Therefore, PLD catalysis in emulsion systems seems to be governed by similar in-

terfacial mechanisms of recognition and activation as in aqueous systems. The phy-

sico-chemical properties of the organic solvent, together with the structure of the

acceptor alcohol, decisively influence the ratio of transphosphatidylation to hydro-

lysis rates, with the same tendencies for different PLDs (Hirche and Ulbrich-Hof-

mann, 2000). Small amounts of aliphatic alcohols are able to activate PLD in hexane

systems which are almost inert without alcohols. An activation by water-miscible

organic solvents, which correlated with the solvent polarity, was also observed

with PI-PC (Wu and Roberts, 1997).

Both PLA 2 (Misiorowski and Wells, 1974; Rakhimov et al., 1986; Wu and Lin,

1994; Morgado et al., 1995) and PLD (Subramani et al., 1996) have been described to

be active also in water-poor organic solvents such as diethyl ether or isooctane,

where they are entrapped in the interior of reverse micelles formed by PC and addi-

tional surfactants. Modification of the properties of phospholipases can be also

reached by modification with methoxypolyethylene glycol (Matsuyama et al.,

1991), lipid-coating (Okahata et al., 1995) or immobilization (see Chapter 13).

12.5 Examples of application

Phospholipids and their partial hydrolysis products, the lysophospholipids, have nu-

merous applications in the food, cosmetic, pharmaceutical, and other industrial

branches (Cevc, 1993). Due to their amphiphilic nature, phospholipids are good

emulsifiers or mediators of solubility, besides being distinguished by their good

biocompatibility and biodegradability. Their tendency to form supramolecular struc-

tures (see Section 12.4.1) allows them to be used as vesicles for the inclusion and the

transport of drugs and other substances. Recently, cationic phospholipids in the form

of liposomes have attracted much attention as transfection vectors in gene therapy

(Yanagihara et al., 1995). Finally, some phospholipids or phospholipid analogs

(phosphatidylnucleosides, plasmalogens, alkylphosphate esters) themselves are bio-

logically active compounds, acting as antitumor agents (Houlihan et al., 1995) and

lung surfactants (references in Namba, 1993). The structural variations of natural

phospholipids allows their physico-chemical properties to be varied as emulsifiers

or vesicle materials, as well as in the design of new potential drugs.

For transformation of natural phospholipids, or for selected steps in the synthetic

production of phospholipids, phospholipases are valuable tools because of their re-

gio- and stereoselective catalysis. In addition to phospholipases, esterases (lipases),

phosphatases and kinases are also used for this purpose. The synthetic applications of

phospholipases are summarized in the following examples. Reviews on phospholi-

pases as catalysts can also be found in Mukherjee (1990), Ko ̈tting and Eibl (1994),

D’Arrigo and Servi (1997) and Servi (1999).

238 12 Phospholipases Used in Lipid Transformations