Flow Injection Analysis of Lactate and Lactate Dehydrogenase Using an Enzyme Membrane in Conjunction with a Modified Electrode

Abstract

A modified electrode for H₂O₂ oxidation, consisting of Pd/Au sputtered on carbon was covered with a lactate oxidase membrane and used in a FIA manifold for selective determination of lactate. The linear range was 0.01-3 mM lactate and up to 200 samples per hour were measured with a relative standard deviation of 1%. Interferences from ascorbic acid and NADH were small because of the low potential of the modified electrode. The lactate oxidase membrane electrode was also used for measurement of lactate dehydrogenase activity using direct injection of the sample into a carrier stream containing pyruvate and NAD⁺.     

Selective Enzymatic Determination of L-Phenylalanine and Phenyl-Pyruvate

Abstract

A simple enzymatic end point method for the determination of L-phenylalanine and 3-phenylpyruvate has been developed. The assay is based on the spectrophotometry determination of NADH formed or degraded in the reaction catalyzed with Thermoactinomyces intermedins phenylalanine dehydrogenase. This method enables the simple and selective determination of L-phenylalanine and 3-phenylpyruvate based on the high substrate specificity of the enzyme. The assay is sensitive in the range of 0.015?0.15 umol of L-phenylalanine and 3-phenylpyruvate.     

Quinohemoprotein alcohol dehydrogenase-based reagentless amperometric biosensor for ethanol monitoring during wine fermentation

This paper describes the development and optimization of an amperometric biosensor for monitoring ethanol in beverages. The biosensor is constructed by cross-linking a quinoprotein alcohol dehydrogenase (QH-ADH) to an Os-complex-modified poly(vinylimidazole) redox polymer using poly(ethylene glycol) diglycidyl ether. The optimum biosensor configuration was evaluated by changing the ratio between enzyme, redox polymer, and cross-linker using conventional graphite rods as basis electrodes. The optimized sensor showed a sensitivity of 0.336±0.025 A M⁻¹ cm² for ethanol and a detection limit (calculated as three times the signal-to-noise ratio) of 1 μM.This biosensor configuration was further evaluated in a conventional flow-injection system and the applicability for the determination of ethanol in diverse wine samples could be successfully demonstrated. Adaptation of this sensor configuration to screen-printed (SP) electrodes allowed their integration into an automated sequential-injection analyzer and the successful on-line monitoring of ethanol during wine fermentation processes.     

活性染料与酶蛋白之间的亲和作用

活性染料与酶蛋白之间有着特异性的亲和作用，可用于亲和层析或亲和分配提取蛋白质。染料末端结构的微小修饰会引起亲和作用的显著变化，且染料载体不同对亲和作用也有一定的影响。以游离活性染料为亲和配基，提出了从组织匀浆液中提取乳酸脱氨酶的二次萃取流程。     

Enzymatic Determination of Methylmercury Traces using Alcohol Dehydrogenase from Baker’s Yeast

 Methylmercury as well as mercury (II) were found to be effective inhibitors of the catalytic activity of alcohol dehydrogenase from baker’s yeast in the reaction of ethanol oxidation by nicotinamide adenine dinucleotide. It was stated that the methylmercury inhibitory action belonged to the non-competitive type, whereas Hg(II) inhibited the enzyme according to the mixed type. The inversely proportional dependence of the indicator reaction rate on the concentration of methylmercury allowed to develop an enzymatic procedure for its determination with a detection limit of 3 nM. The possibility of methylmercury determination in presence of mercury (II) and mercury (II) determination in presence of methylmercury (concentration ratios CH₃Hg⁺:Hg(II) were 1:1 and 1:10, respectively) was shown. In the first case masking reagents, DEDTC or thiourea, were used to form stable complexes with Hg(II). Received February 9, 2001; accepted August 10, 2001; published online June 24, 2002     

用吐温80—盐—水液—固萃取体系从兔肌中分离纯化乳酸脱氢酶

用吐温８０－盐－水液－固萃取体系从兔肌中分离纯化乳酸脱氢酶＊柳畅先邓江天雷锦桂游文淑李步海（中南民族学院化学系武汉４３００７４）关键词液－固萃取吐温８０乳酸脱氢酶中图分类号Ｏ６５８．２非有机溶剂液－固萃取体系是一种新的萃取体系，其特点之一是聚合物固相...     

乳酸脱氢酶的流动注射分析—电化学检测体系的研究

本文研究了L－乳酸盐＋NADLDH／→/←丙酮酸＋NADH＋H^ 的酶反应动力曲线及NADH的电化学性质与流动伏安检测法，建立了乳酸脱氢酶（LDH）的单泵单液路流动注射分析－电化学检测体系，可测定LDH的活性和浓度。     

D-lactate dehydrogenase

This note compares the substrate specificity of D-lactate dehydrogenase (D-LDH, EC 1.1.1.28) to that of L-lactate dehydrogenase (L-LDH, EC 1.1.1.27), illustrates three procedures that use D-LDH in synthesis and two methods for recycling NADH, and provides experimental details illustrating the use of D-LDH in organic synthesis.     

Enzymatic Biosensors Based on Carbon Nanotubes Paste Electrodes

The performance of enzymatic biosensors based on the immobilization of different enzymes within a carbon nanotubes paste electrode (CNTPE) prepared by dispersion of multi‐wall carbon nanotubes (MWNT) and mineral oil is reported in this work. The strong electrocatalytic activity of carbon nanotubes towards the reduction of hydrogen peroxide and quinones and the oxidation of NADH have allowed an effective low‐potential amperometric determination of lactate, phenols, catechols and ethanol, in connection with the incorporation of lactate oxidase, polyphenol oxidase and alcohol dehydrogenase/NAD⁺, respectively, within the composite matrix. Compared to the analogous enzymatic CPEs, a great enhancement in the response is observed at the enzymatic CNTPEs. Therefore, highly sensitive lactate, phenols, catechols and alcohols biosensors without using any metal or redox mediator can be obtained with this new composite material.