Synthesis of phosphatidylserine with phospholipase D from streptomyces sp.

Abstract

For the efficient production of phospholipase D from Streptomyces sp., the suitable composition of the culture medium was determined by a fractional factorial experimental design. The composition of the medium was as follows; 15 g/L of Bacto-peptone, 5 g/L of yeast extract, 20 g/L of glucose, 6 g/L of $CaCO_3$. The activity of phospholipase D from Streptomyces sp.in a culture supernatant was 5.62(unit/mL). The synthesis of phosphatidylserine with phospholipase D from Streptomyces sp in the two-phase system was carried out by using phosphatidylcholine as the donor and serine as the acceptor. The yield of phosphatidylserine in a two-phase system was found to be better than that obtained in an emulsion system. In the case of serine, the initial rate of transphosphatidylation was higher with D-serine than with L-serine when the PLD from Streptomyces sp was used. Among the various solvents tested, PLD showed the most efficient catalytic activity and stability in butylacetate. In order to find the optimum conditions for the synthesis of PS several different conditions were tried. Among these the highest yield of PS was obtained at 40℃, pH of 5.5 - 7.5, 400 rpm, above 0.1 mmol of $Ca^{2+}$ and 1.5 mmol of L-serine. This experiment showed the ratios of the solvent/water to be very important e.g. the higher the ratios of the solvent/water, the better the catalytic activity and selectivity. When the ratios of the solvent/water increased ranging from 1:1 to 5:1, the conversion and selectivity of PS were notably improved and in these conditions a smaller amount of serine could produce the same yield of product. The reusability of PLD was also examined; this was found not to be efficient because of the instability of PLD in butylacetate.