Study On Production Of L-Phe By Immobilized Cell

L-Phe is one of the eight kinds of essential amino acid. We can use it to produce adrenalin, thyroxin, melanin and aspartame especially. Recently, it has been proved that L-Phe has the function of making brain clearer, helping losing fat and treating cancer。Transforming PPA to L-Phe with immobilized cells is one of the best ways to produce L-Phe. This experiment used different ways to immobilize E.Coli. The material used in cell immobilization contains chitosan, Dialyse memberane and fibre memberane reactor. The enzyme reaction dynamics on free cells and immobilized cells was researched. The characteristics of enzyme reaction had been obtained. These will be very helpful to explore the production technology of L-Phe.In the enzyme reaction of free cells, the optimum pH is 8.0, the optimum temperature is 37℃ and the initial velocity is within the range of 20-90 minutes. When cell loading is 1.17% -5.50%, the velocity of the reaction is linear with cell loading, the high the cell loading, the rapid the velocity. When pH is 8.0 and temperature is 37℃, the parameters for dynamics equation are Vm=0.0109mol ·L-1·h-1, Ka=0.0089 mol · L-1, Kb=0.0037 mol · L-1. When substrate concentration are too high, the reaction can be promoted. Contrarily, the reaction can be restrained when production is too much .36.1% enzyme activity is saved after cells are immobilized with chitosan. In enzyme reaction of chitosan immobilized cells, the optimum pH is 8.0, the optimum temperature is 37℃ and the initial velocity is within the range of 30-240 minutes. When cell loading is 3.33% -13.3%, the velocity of the reaction is linear with cell loading, the high the cell loading, the rapid the velocity. When pH is 8.0 and temperature is 37℃, the parameters for dynamics equation are Vm=0.043mol ·L-1·h-1, Ka=0.0697 mol · L-1, Kb=0.000098 mol · L-1. The enzyme activity half-life of immobilized cells is about 2-3 days and the half life of its transformation rate is more than 8 days. The decrease of the enzyme activity is due to the cell leakage andsomething else.Embeding cells with dialysis membrane and fiber membrane reactor can also get immobilized cells. When the cells are immobilized, the more the cell loading, the higher the enzyme activity, but the lower the recovery rate of enzyme activity. For dialysis membrane immobilized cells and fiber membrane reactor immobilized cells respectively, the recovery rate of enzyme activity is 24% and 21%, the initial velocity is within the range of 10-120 minutes and 10-180 minutes , the half-life of enzyme activity is about 14 days and 25 days, the half-life of transformation rate is about 20 days and more than 27 days.The experiment shows that the enzyme activitiy of immobilized cells is lower than that of free cells. But the immobilized cells can be used repeatedly and do not bring pollution to reaction system, so that it can make production separating more easily. In three kinds of cell immobilization above, membrane reactor is the best material, dialysis membrane is next and chitosan is the last. Immobilizing cells with memberane is simple and inexpensive. It will become a very good way to. transform PPA to L-Phe in industry.