A facile transphosphatidylation reaction using a culture supernatant of actinomycetes directly as a phospholipase D catalyst with a chelating agent.

An attempt was made to use the phospholipase D (PLD)- containing culture supernatants of actinomycetes directly as catalysts for the transphosphatidylation reaction of phosphatidylcholine (PC) to phosphatidylethanolamine (PE) in a biphasic system. Of the five actinomycetes (three Streptomyces sp. and two Streptoverticillium sp.) examined, three (St. mediocidicus, Stv. cinnamoneum and Stv. hachijoense) exhibited good PLD production performance, but the selectivity (ratio of transphosphatidylation to hydrolysis) of the PLDs in the culture supernatant of all three actinomycetes were significantly low. However, the addition of EDTA to the reaction mixture as a chelating agent remarkably improved the selectivity of the PLDs, which approached 100% in all the culture supernatants. Commercially available PLDs were also investigated and classified into two types. The PLDs of one type had high selectivity and no metal was required for the enzyme activity, while those of the other type showed low selectivity and a metal was necessary for the enzyme to be activated. From this finding, it was considered that the culture supernatants used in this study contained several PLDs of both types. When the chelating agent was added to the reaction mixture, the hydrolysis due to PLDs with low selectivity was suppressed by removal of the essential metal, resulting in an increased in the overall selectivity of the PLDs in the culture supernatant. Repeated batch transphosphatidylation reactions were performed 20 times, reusing the PLDs in the aqueous phase by centrifugation; the reaction rate gradually decreased to 60% of that of batch 1 by batch 20. This suggests that the transphosphatidylation reaction using a culture supernatant has potential for industrial application. (c) 1994 John Wiley & Sons, Inc.