Enzymatic biosensors are often used to detect trace levels of some specific substance. An alternative methodology is applied for enzymatic assays, in which the electrocatalytic kinetic behavior of enzymes is monitored by measuring the faradaic current for a variety of substrate and inhibitor concentrations. Here we examine a steady-state and pre-steady-state reduction of H2O2on the horseradish peroxidase electrode. The results indicate the substrate-concentration dependence of the steady-state current strictly obeys Michaelis-Menten kinetics rules; in other cases there is ambiguity, whereby he inhibitor-concentration dependence of the steady-state current has a discontinuity under moderate concentration conditions. For pre-steady-state phases, both catalysis and inhibition show an abrupt change of the output current. These anomalous phenomena are universal and there might be an underlying biochemical or electrochemical rationale.Keywords:enzymatic kinetics;inhibition;anomalous behavior;electrochemical biosensor
Tae Sik Sung,Seung-Bum Ryoo,Chang-Hyun Lee,Seon-Min Choi,Joo-Won Nam,Hyun-Bok Kim,Ji young Lee,Jung-Dae Lim,Kyu Joo Park,Hyun-Tai Lee
The fruit ofMorus albaL. (MAF) has been consumed as a food worldwide. MAF has also been widely used in traditional medicine for thousands of years in East Asia, and its diverse bioactivities have been reported in numerous publications. However, no prokinetic activity has been reported for MAF or its components. In the present study, therefore, we investigated the effects of MAF on gastrointestinal motor function by measuring the intestinal transit rate (ITR) of Evans blue in mice in vivo. The ITR values accelerated by MAF were significantly higher than those accelerated by cisapride or metoclopramide, suggesting that MAF has potential as a new prokinetic agent to replace cisapride and metoclopramide. We also investigated the effects of MAF on myogenic and neurogenic contractions in human intestinal smooth muscles by measuring spontaneous contractions of smooth muscle strips, smooth muscle contractions induced by neural stimulation, and migrating motor complexes from intestinal segments in the human ileum and sigmoid colon in situ. MAF increased both myogenic and neurogenic contractions to enhance ileal and colonic motility in the human intestine. Taken together, these results indicate that MAF enhanced intestinal motility by increasing both myogenic and neurogenic contractions, thereby accelerating the ITR.Keywords:intestinal transit;Morus alba;mulberry fruit;myogenic contraction;neurogenic contraction;prokinetic;smooth muscle
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