ABSTRACT
Catalase is widely used in the food, medical, and textile industries. It possesses exceptional properties including high catalytic efficiency, high specificity, and environmental friendliness. Free catalase cannot be recycled and reused in industry, resulting in a costly industrial biotransformation process if catalase is used as a core ingredient. Developing a simple, mild, cost-effective, and environmentally friendly approach to immobilize catalase is anticipated to improve its utilization efficiency and enzymatic performance. In this study, the catalase KatA derived from Bacillus subtilis 168 was expressed in Escherichia coli. Following separation and purification, the purified enzyme was prepared as an immobilized enzyme in the form of enzyme-inorganic hybrid nanoflowers, and the enzymatic properties were investigated. The results indicated that the purified KatA was obtained through a three-step procedure that included ethanol precipitation, DEAE anion exchange chromatography, and hydrophobic chromatography. Then, by optimizing the process parameters, a novel KatA/Ca3(PO4)2 hybrid nanoflower was developed. The optimum reaction temperature of the free KatA was determined to be 35 ℃, the optimum reaction temperature of KatA/Ca3(PO4)2 hybrid nanoflowers was 30-35 ℃, and the optimum reaction pH of both was 11.0. The free KatA and KatA/Ca3(PO4)2 hybrid nanoflowers exhibited excellent stability at pH 4.0-11.0 and 25-50 ℃. The KatA/Ca3(PO4)2 hybrid nanoflowers demonstrated increased storage stability than that of the free KatA, maintaining 82% of the original enzymatic activity after 14 d of storage at 4 ℃, whereas the free KatA has only 50% of the original enzymatic activity. In addition, after 5 catalytic reactions, the nanoflower still maintained 55% of its initial enzymatic activity, indicating that it has good operational stability. The Km of the free KatA to the substrate hydrogen peroxide was (8.80±0.42) mmol/L, and the kcat/Km was (13 151.53± 299.19) L/(mmol·s). The Km of the KatA/Ca3(PO4)2 hybrid nanoflowers was (32.75±2.96) mmol/L, and the kcat/Km was (4 550.67±107.51) L/(mmol·s). Compared to the free KatA, the affinity of KatA/Ca3(PO4)2 hybrid nanoflowers to the substrate hydrogen peroxide was decreased, and the catalytic efficiency was also decreased. In summary, this study developed KatA/Ca3(PO4)2 hybrid nanoflowers using Ca2+ as a self-assembly inducer, which enhanced the enzymatic properties and will facilitate the environmentally friendly preparation and widespread application of immobilized catalase.
Subject(s)
Catalase , Nanostructures/chemistry , Hydrogen Peroxide/metabolism , Enzymes, Immobilized/chemistry , CatalysisABSTRACT
Objective To study the relationship between the bile flow and CCK, GAS and SEC hormones in the rabbits after traumatic stress. Methods Bile flow was counted by bile duct intubation and the models of traumatic stress were produced by cutting the hind legs of rabbits. Bile flow, CCK, GAS and secretin in plasma were measured before and after stress. Results Bile flow after traumatic stress was significantly increased (P
ABSTRACT
Anopheles minimus was infected with Plasmodium yoelii yoelii under adequate condition. The malaria parasite could develop normally and produce mature oocysts containing sporozoites. Large numbers of free active sporozoites were found in the haemocele but most of them failed to penetrate into the mosquito's salivary glands. Thus the sporogonic cycle of the parasite could not be completed.But in one mosquito, a few sporozoites were found in its salivary glands. It seems that there is an individual difference in the susceptibility of the mosquitoes and this throws some light on the possibility of selecting a susceptible strain of A. minimus to establish the A. minimus-P. yoelii system for malaria research.