Phospholipase transphosphatidylation reaction

M. Takami and Y. Suzuki Synthesis of novel phosphatidyldihydroxyacetone via transphosphatidylation reaction by phospholipase D. Bioscience, Biotechnology, and Biochemistry 58 (1994) 2136-2139. 

Phospholipase D catalyzes the hydrolysis of phospholipids to produce phosphatidic acid and the corresponding polar head group [215]. In most systems, including neutrophils, phosphotidylcholine is the preferred substrate. Two mammalian isoforms of the enzyme have been cloned, but PLD purified from human neutrophils displays different biochemical characteristics, suggesting it represents a unique isoform [139, 215], In the presence of primary alcohols, PLD catalyzes a transphosphatidylation reaction that produces the corresponding phos-phatidylalcohol. This transphosphatidylation reaction effectively competes with hydrolysis, and thus alcohols such as ethanol and 1-butanol are frequently used experimentally as inhibitors of PLD-catalysed PA production. 

For example, an isozyme of glutathione-S-transferase will also catalyze the fatty acid ethyl-ester synthase reaction, leading to the formation of ethyloleate from oleic acid and ethanol (Bora et al. 1989). Also, phospholipase D catalyzes the transphosphatidylation of phosphatidylcholine with ethanol to form phosphatidylethanol (Kobayashi and Kanfer 1987). The active site requirements and kinetics of the hydrolases or transferases that catalyze these ethylation reactions are not well understood. The elucidation of mechanisms and active site structures for enzyme-catalyzed... 

Phospholipase D (EC 3.1.4.4) is a lipolytic enzyme that hydrolyzes the terminal phosphodiester bond on PLs. Due to its ability to transfer the phosphatidyl moiety of glycerophospholipids to various alcohols (transphosphatidylation), PLD is also used to synthesize PLs with desired head groups that are poorly accessible via the chemical route (Figure 23.4). This ability has been utilized for the synthesis of natural PLs that are rare in nature, such as PG and PS. Novel types of PLs (phosphatidyl-X) have also been synthesized via PLD-mediated transphosphatidylation to add the amphiphilic properties of PLs to the acceptor compounds. These reactions are typically carried out in biphasic systems with water (containing PLD or a hydrophilic alcohol acceptor) and an organic solvent such as chloroform, ether, ethyl acetate, benzene, or toluene. 

Whether the aoove reactions play any role in lipid biosynthesis is open to question. The naturally occurring phosphatidylglycerol is the optically active -T-j -glycerol enantiomer. Yang et al. (1967) found that the product of transphosphatidylation was a racemic mixture, although more recently Batrakov et al. (1975) found evidence for stereospecificity in the acyl transfer reaction with phospholipase D. 

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