Study On The Enzyme Catalytic Synthes Is Process Of Phosphatidylserine Based On The Effective Use Of L-serine

Phosphatidylserine (PS), a rare phospholipid, is the basic material for human life. It can affect the transmission of brain information, help the storage and reading of the brain memory, which is known as a burgeoning "smart nutrients" after the choline and "brain gold" DHA. However, PS is extremely scarce in nature, in order to meet human demand, phosphatidylserine is prepared using enzyme conversion method. But in the process of synthesising PS by the enzymic method of phospholipase D, we make reaction substrate L-serine be greatly excessive to obtain high yield of PS product, which is about 100 times of the other substrate PC in terms of the molar content, resulting in almost 99% waste of L-serine. To save costs, the recovery of L-serine is a must.This paper focuses on the two-phase reaction system, the transformation of soybean lecithin(PC) to PS catalyzed by phospholipase D(PLD). According to the literature, on the basis of having determined the optimum conditions of synthesising PS, the possible catalytic mechanism of PLD is assumed. The influence factors of enzymatic reaction were studied, and a kinetic model is established.The reaction model was evaluated at various process conditions, the matched-degree between the data simulated by the reaction model and the experimental data was relatively higher, which demonstrated that the reaction model is reasonable and reliable. Depending on the reaction model, the effect of by-product and substrate of the reaction catalyzed by PLD is analyzed:when PS is synthesized, the substrate L-serine is greatly excessive, resulting in the waste of raw materials, and propose the necessity of recycling L-serine. With the increase of PC concentration, choline production increases proportionately, the recovered L-serine will be mixed with a certain amount of choline, which inhibits the enzyme reaction rate and reduces the yield of PS, then impacts the repetitive utilization of L-serine.The solubility of L-serine in alcohol-water system was determined, and the effect of alcohol concentration, pH, choline concentration on the solubility of L-serine was investigated. The study found that with the increase of alcohol concentration, the solubility of L-serine decreased, because the addition of ethanol greatly reduces the dielectric constant of the solution; L-serine is amphoteric substance, too acidic or alkaline solution will promote the ionization, the solubility was the least near the isoelectric point of 5.68; The solubility of L-serine decreased with the increase of the concentration of choline. And according to the alcohol water dissolving balance of L-serine, the excessive L-serine in the reaction solution was recovered using the ethanol recrystallization, the optimal recovering conditions were determined as following:the enrichment concentration of water phase is 18%, the dosage of ethanol is 10 ml, pH is 5.5, crystallization temperature is 10?, the rotate speed is 250rpm. The recovery rate of L-serine is high, which is about 90%, the purity is also high, the amount of choline in lg recovered L-serine is up to 0.56%.In order to verify the recyclability of L-serine, we rebuild the PS synthesis process based on the recycling of L-serine, and apply the recovered L-serine to the synthesis reaction of PS, repeating five times. The study found that, adding a small amount of fresh L-serine to the reaction system, the reduction of the yield of PS is small. The reusebility of L-serine is good. And in the single water phase, repeating recovery operations can achieve similar effect.