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Gamma-aminobutyric acid (GABA) is an vital neurotransmitter, and the reaction to obtain GABA through biocatalysis requires coenzymes, which are therefore limited in the production of GABA. In this study, polyacrylamide hydrogels doped with chitosan and waste toner were synthesized for glutamate decarboxylase (GAD) and coenzyme co-immobilization to realize the production of GABA and the recovery of coenzymes. Enzymatic properties of immobilized GAD were discussed. The immobilized enzymes have significantly improved pH and temperature tolerance compared to free enzymes. In terms of reusability, after 10 repeated reuses of the immobilized GAD, the residual enzyme activity of immobilized GAD still retains 100% of the initial enzyme activity, and the immobilized coenzyme can also be kept at about 32%, with better stability and reusability. And under the control of no exogenous pH, immobilized GAD showed good performance in producing GABA. Therefore, in many ways, the new composite hydrogel provides another way for the utilization of waste toner and promises the possibility of industrial production of GABA. [ABSTRACT FROM AUTHOR]

The search for seeking novel immobilized enzyme carriers is a hot topic in the field of enzyme engineering. As a kind of common office consumable, magnetic printing toner has been terribly wasted, leading to potential harm to the environment. We try to use printing toner as carrier for enzyme immobilization to realize waste reuse. In this paper, the laccase extracted from Agaricus bisporus was successfully immobilized on chitosan coated magnetic printing toner by glutaraldehyde linking. The use of printing toner is proved to be feasible. The results show that the optimal temperature of immobilized laccase is 40 °C, and the optimal pH is 3.0. Compared with free laccase, the optimal temperature and optimal pH have been obviously changed after immobilization. And the pH tolerance has been significantly improved, which can remain 53% activity after 5 cycles. Because of the use of magnetic printing toner, it is more convenient to recycle the immobilized enzyme. In this study, printing toner was used as carrier for the immobilization of enzyme and the discarded printing toner recycling was realized. • The immobilized enzyme carrier with printing toner as the main body was successfully constructed. • Laccase was successfully immobilized with the new carrier. • The new carrier uses discarded print toner to reduce environmental pollution. [ABSTRACT FROM AUTHOR]

• A co-immobilization system of dual-enzyme and coenzyme was successfully constructed. • The immobilized enzymes presented improved stability and fine reusability. • The system realized chiral (R)−1-phenylethanol highly selective production and coenzyme effective recycling. Coenzymes are required in the reaction catalyzed by oxidoreductases. The research on coenzyme regeneration has always been a hot topic in the field of biological catalysis. In this work, we tried to construct a co-immobilization system of glucose dehydrogenase (GDH), (R)-1-phenylethanol dehydrogenase ((R)-PEDH) and coenzyme with functional magnetic nanoparticles as carriers, so as to realize chiral (R)-1-phenylethanol highly selective production and coenzyme effective recycling. The enzymatic properties of immobilized enzymes were explored. The results showed that the immobilized enzymes had improved stability and fine reusability. In addition, during the catalytic coupling reaction at a final concentration of 2.63 μM NAD+, the total turnover number (TTN) was as high as 924, and the volumetric productivity of (R)-1-phenylethanol was 37.06 mg·L−1·h−1. After reused for 10 cycles, the catalytic efficiency of immobilized coenzyme can still be maintained at more than 30%. From multiple perspectives, the immobilized dual-enzymes and coenzyme system seems to be a multifunctional system for (R)-1-phenylethanol production and coenzyme regeneration. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fluorinated 10-hydroxycamptothecin and SN 38 were prepared by four steps. [•] Fluorinated camptothecin derivative MF-6 showed potent antiproliferative activities. [•] We have obtained potent camptothecin derivatives by fluorine substitution strategy. [•] C-21 carbonyl group of camptothecin is unnecessary to antitumor activity. [Copyright &y& Elsevier]