The Interdependence of Solvent, Acceptor Alcohol and Enzyme Source in Transphosphatidylation by Phospholipase D

Abstract

Phospholipases D (PLDs) from different sources differ in their transphosphatidylation and hydrolysis rates. These properties, however, are strongly influenced by the reaction system and the acceptor alcohol. To analyze the interdependence of enzyme source, organic solvent and acceptor alcohol with respect to the catalyzed reactions, PLDs from cabbage and two different Streptomyces spp. were compared in their hydrolysis and transphosphatidylation rates in the reactions of phosphatidylcholine with glycerol, 1-butanol and several choline analogs in diethyl ether/buffer and hexane/buffer systems. The total activities of the enzymes which differed widely for the different solvents, followed the same tendency for all PLDs examined supporting the hypothesis that the structure of the phospholipid aggregates, which varies according to the medium, is very important for enzymatic activity. Also the ratio of transphosphatidylation to hydrolysis rates was influenced by the solvent in the same way for different PLDs. With all enzymes, however, this ratio was strongly dependent on the hydrophilic or amphophilic nature of the acceptor alcohol. Transphosphatidylation is strongly preferred over hydrolysis with the amphiphilic 1-butanol in the hexane system, whereas no reaction occurs with the hydrophilic glycerol in the same system unless a small amount of 2-butanol is added as mediator. Finally, it has been shown that small variations of the molecular structure of the acceptor alcohols such as in a series of different positively charged N-heterocyclic alcohols may dramatically change the ratios of transphosphatidylation to hydrolysis rates for different PLDs.

Key Words:

• Phospholipase D
• Cabbage
• Streptomyces
• Organic solvent
• Transphosphatidylation