The essence of enzymes is to keep the homeostasis and balance of humans by catalyzing metabolic responses and modulating cells. Suppression of an enzyme slows the progress of some diseases, making it a therapeutic target. Therefore, it is important to develop enzyme inhibitors by proper bioactivity screening strategies for the future treatment of some major diseases. In this review, we summarized the recent (2015–2020) applications of several screening strategies (electrophoretically mediated microanalysis, enzyme immobilization, affinity chromatography, and affinity ultrafiltration) in finding enzyme inhibitors from certain species of bioactive natural compounds of plant origin (flavonoids, alkaloids, phenolic acids, saponins, anthraquinones, coumarins). At the same time, the advantages and disadvantages of each strategy were also discussed, and the future possible development direction in enzyme inhibitor screening has been prospected. To sum up, it is expected to help readers select suitable screening strategies for enzyme inhibitors and provide useful information for the study of the biological effects of specific kinds of natural products.
Myosin light chain kinase (MLCK) is a regulatory protein for smooth muscle contraction, which acts by phosphorylating 20-kDa myosin light chain (MLC20) to activate the myosin ATPase activity. Although this mode of action is well-established, there are numerous reports of smooth muscle contraction that is not associated with MLC20 phosphorylation. The kinase activity for the phosphorylation is localized at the central part of MLCK, which is also furnished with actin-binding activity at its N terminal and myosin-binding activity at its C terminal. This article overviews as to how such multifunctional properties of MLCK modify the actin-myosin interaction and presents our observations that the phosphorylation is not obligatory in induction of smooth muscle contraction.
The main purpose of the present study was to investigate the prototypes and oxidation products of alkaloids with the use of an online electrochemistry/quadrupole time-of-flight mass spectrometry system. The metabolism of oxidative phase I and II was simulated in an electrochemical reaction cell. The metabolic processes for coptisine and jatrorrhizine were simulated in a thin-layer cell fitted with a glassy carbon working electrode, while the metabolic processes for berberine and palmatine were simulated by using a boron-doped diamond working electrode. By using the new experimental system, dehydrogenation, demethylation, methylation, hydroxylation, and the formation of two hydroxylation adducts were detected by applying different potentials to the electrochemical cell. The online reaction with glutathione yielded different covalent glutathione adducts. The results obtained from the electrochemical simulation were found to be in good accordance with those reported previously in vivo, showing that electrochemistry/mass spectrometry is an effective tool for studying metabolic reactions for various complex components. Moreover, analysis of alkaloids in liver microsomes by liquid chromatography coupled with mass spectrometry confirmed the possibility of using an electrochemistry technique to simulate the metabolism of target compounds.
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