A BSTRA C T Polyphenol oxidase (EC 1.14.18.1)

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Aminoacylase I (EC. 3.5.1.14) was immobilized by covalent crosslinking to alginate molecules with 1‐ethyl‐3‐(3‐dimethyl‐aminopropyl)‐carbodiimide HCl followed by calcium alginate bead formation for the production of L‐phenylalanine from the racemic mixtures of N‐acetyl‐DL‐phenylalanine. Different concentrations of the coupling reagent were tested and the coupling process was optimized. The immobilized and the partially purified aminoacylase were characterized in terms of the activity, operational stability, thermal stability, pH and temperature optima and kinetic constants, Km and Vmax. The activity of the enzyme covalently immobilized in calcium alginate beads was enhanced by about 75% compared to that of free enzyme. The beads showed stable activity under operational conditions, they lost about 40% of their activity after four reaction cycles. The immobilized aminoacylase was more stable over a broader pH range. Thus this simple method provides irreversible immobilization of aminoacylase to give a biocatalyst with good operational stability and enhanced activity.

Hydroxyapatite particles were prepared by coprecipitation of calcium and phosphate solutions in the presence or absence of an emulsifier followed by physical treatments. The morphology of the particles was examined by SEM and particle size distribution was determined by Zetasizer nano-series. The particle size was also determined by SEM and TEM. The particle size distribution and morphology of the particles were found to be dependent on the chemicals used and the conditions and methods of physical treatment. Micro-hydroxyapatite and nano-particles in the size range of 60 nm -300 µm have been prepared. Under careful controlled conditions with the use of coprecipitation of solution mixtures of calcium chloride, phosphoric acid and an emulsifier followed by physical treatments using autoclave, sonication and calcination, rod-shape hydroxyapatite nanoparticles of dimension of (68 x 24) ± 5 nm were obtained.

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Aminoacylase I (E.C.3.5.1.14) was immobilized by entrapment in calcium alginate beads coated with polyethyleneimine for the production of L-phenylalanine by the hydrolysis of a racemic mixture of N-acetyl-DL-phenylalanine. The operational stability in terms of batch operation and continuous reaction in packed-bed bioreactor were studied. Kinetic constants, Km and Vmax values of free and immobilized enzymes were studied. Polyethyleneimine treatment was found to enhance the operational stability of the enzyme though its activity was substantially reduced. When polyethyleneimine-coated calcium alginate beads were packed into packed bed bioreactor, it was stable for at least 25 days under continuous operation without appreciable loss of activity.