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Construction of multi-enzymatic cascade reaction system of co-immobilized hybrid nanoflowers for efficient conversion of starch into gluconic acid.

Introducing an efficient method for the rapid conversion of starch into gluconic acid is desirable to solve the current problems existing in traditional gluconic acid preparation processes. In this study, a robust and easy-to-use multi-enzymatic cascade reaction system of co-immobilized GA@GOx hybrid nanoflowers with a specific spatial distribution of enzymes by compartmentalization was constructed and applied to catalyze starch to gluconic acid in one pot. In the preparation processes, the glucose oxidase (GOx) hybrid nanoflowers were first synthesized via self-assembly mechanism and then glucoamylase (GA) was adsorbed on the surface of GOx hybrid nanoflowers through the interaction of Cu2+ and amino acids of GA. The optimum preparation conditions and reaction parameters of the GA@GOx hybrid nanoflowers had been investigated. In addition, the morphology, composition and crystallization of the GA@GOx hybrid nanoflowers had been fully studied. Based on the lower Km, the GA@GOx hybrid nanoflowers with compartmentalization had better effect of the substrate channeling on the catalytic efficiency. The final results indicated that the overall enzyme activity of the GA@GOx hybrid nanoflowers increased by 1.5 times, and the conversion efficiency was 92.12% within 80 min significantly superior to the free enzyme system, which showed the outstanding conversion of starch into gluconic acid in one pot.