Front Matter

transduction, membrane trafficking, etc., has been realized (reviewed in Tischfield,

1997; Balsinde and Dennis, 1997; Rhee and Bae, 1997; Exton, 1997; Leslie, 1997).

In biocatalysis, selected phospholipases (PLA 2 , PLD) have been applied for several

decades (see Section 12.5.). Stimulated by the progress in enzyme technology, the

interest in the application of phospholipases has also increased in recent years, and a

further impetus is expected due to the present strong progress in gene technology.

12.2.1 Phospholipase A 1

Enzymes possessing PLA 1 activity have been described as intracellular, membrane-

bound or soluble enzymes from rat liver lysosomes (Waite et al., 1981), bovine testis

(Higgs et al., 1998),Aspergillus oryzae(Watanabe et al., 1999),E. coli(Scandella

and Kornberg, 1971; Nakagawa et al., 1991),Corticium centrifugum(Uehara et al.,

1979), hornet venom (Soldatova et al., 1993), tobacco hornworm (Nieder and Law,

1983) and other sources (references in Van den Bosch, 1980) as well as extracellular

forms fromTetrahymena pyriformis(Arai et al., 1986) orTetrahymena thermophila

(Guberman et al., 1999). Hitherto, PLA 1 , however, has been poorly studied system-

atically and scarcely applied in biocatalysis (see Section 12.5.).

12.2.2 Phospholipase A 2

PLA 2 is probably the best investigated lipolytic enzyme, mostly studied from animal

sources. There is a wide spectrum of different PLA 2 s comprising high molecular

weight intracellular (Ca2+-dependent and Ca2+-independent) and low molecular

weight extracellular or secretory enzymes (Dennis, 1994; 1997). Intracellular

PLA 2 s are found in almost every mammalian cell (Van den Bosch, 1980) where

they play manifold roles in membrane metabolism and in the release of arachidonic

acid acting as precursor for the biosynthesis of prostaglandins and leukotrienes.

Mammalian pancreas and venoms from snakes and bees are the richest sources

for secretory PLA 2 s, which have preferably been used for biocatalytic application

(Table 1). Although no recombinant PLA 2 is available commercially, the expression

of PLA 2 s from porcine pancreas (Verheij and de Haas, 1991; Janssen et al., 1999),

bovine pancreas (Noel and Tsai, 1989; Deng et al., 1990; Zhu et al., 1995), snake

venom (Kelley et al., 1992; Chang et al., 1996) and bee venom (Dudler et al., 1992;

Annand et al., 1996) inE. coliwas successful. PLA 2 from porcine pancreas has also

been expressed inSaccharomyces cerevisiae(Bekkers et al., 1991).

AlthoughStreptomyces(Verma et al., 1980; Suzuki and Sugiyama, 1993) and

Aspergillusspp. (Winter et al., 1998) are known to contain PLA 2 , microbial sources

of PLA 2 have taken an inferior part in basic as well as in applied research, probably

because of the good accessibility and high yields of the animal enzymes. PLA 2 is also

reported to occur in plants (Kawakita et al., 1993; Kim et al, 1994; May et al., 1998;

Stahl et al, 1998), the state of research on this enzyme, however, is still in its early

stages.

222 12 Phospholipases Used in Lipid Transformations