Abstract
Alkaline phosphatase originating from placenta was microencapsulated with polystyrene by employing a drying-in-liquid method. The reaction rate of the resultant microcapsules was slower than that of the native enzyme. The kinetic data for both native enzyme and microencapsulated enzyme satisfied the Lineweaver-Burk relationship, but the kinetic parameters were different. When the concentration of substrate was much larger than the Michaelis constant, the reaction kinetics of the native enzyme were zero-order, while those of the microencapsulated enzyme were not. The reaction rate of the microcapcules was affected the amount of polystyrene used as a wall material and by the stirring rate of the reaction system. The reaction still continued, though slowly, after the microcapsules were removed from the system. These findings suggested that the internal diffusion of substrate in microcapsules and the capillary flow of enzyme molecules through a few pin holes on the surfaces of microcapsules were the rate-determining steps of the reaction in the case of the microcapsules. It was confirmed that the enzyme was fairly well immobilized, because sixty percent of the initial enzyme activity in the microcapsules remained even after the microcapsules had been used six times. When the native enzyme was stored at 60°C, the activity fell to a quarter of the initial activity after two hours, whereas microcapsules stored under the same conditions retained 50% of the initial activity.
