Laccases (benzenediol: oxygen oxidoreductases , EC1.10.3.2) can oxidize various substrates, and those which are tolerant to and even activated by salts have attracted a lot of attention due to their application potential in certain industries. The mechanism of the salt activation of laccases is awaiting to be elucidated yet. Our previous study (Li, Xie et al. 2018) supposed that the salt activation of marine laccase Lac15 might be attributed to Cl - ion specifically binding to some local sites to interfere substrate binding and/or electron transfer . In this study, we found two sites whose mutations resulted in elimination of the salt activation of Lac15’s activity towards catechol and dopamine respectively, and revealed that the mutations affected the activity by altering both E m and k cat , demonstrating the supposed mechanism. A model for the salt activation of laccases was accordingly proposed, albeit some details are to be elucidated.
Lijun Xu,Jialin Sai,Dongguo Xue,Lu Zhou,Renjun Pei,Aihua Liu
Graphical The complex formed by Co 2 + , 8 - hydroxyquinoline and HCO 3 − could act as a robust peroxidase mimic in neutral pH at room temperature. This system provided a universal method for the ultrasensitive colorimetric detection of various 8-hydroxyquinoline-based drugs (e. g., clioquinol) by activating the catalytic activity of Co 2+ . 8-Hydroxyquinoline (8HQ) and its derivatives display diverse bioactivities and therapeutic potentials. In this study, we unveiled that 8HQ can boost the peroxidase-like activity of Co 2+ in the presence of bicarbonate (HCO 3 − ) in neutral pH at room temperature. With 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulphonate) (ABTS) as the substrate, the formed Co 2+ /8HQ/HCO 3 − complex shows robust catalytic activity with the turnover number ( k cat ) tens to hundreds of times higher than that of Co 3 O 4 and other Co 2+ complexes in terms of per cobalt ion. This system was used to design colorimetric sensors for ultrasensitive detection of 8HQ-based drugs by activating the activity of Co 2+ . Take detecting clioquinol as an example, a detection limit of 2.4 nM clioquinol with a linear range from 0.01 to 0.2 μM was obtained. This work not only revealed a new kind of ligand that activated the activity of Co 2+ , but also provided a facile, low-cost, ultrasensitive, easy-to-use, and universal strategy for sensing various 8HQ-based drugs. Further development of this catalytic system might be beneficial to overcome drug resistance by combined medication.
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