Choline oxidase Cholinesterase

Another class of enzymes that has found wide application in the biosensor field in the last decades is that of the cholinesterases which have been mainly used for the detection of pesticides. For the amperometric detection of cholinesterase activity, both the substrates acetylcholine and acetylthiocholine have been extensively used [6-9], the latter being preferred because this avoids the use of another enzyme, choline oxidase, which is usually coupled with acetylcholinesterase. However, the amperometric measurement of thiocholine, produced by... 

Serum cholinesterase (acetylcholine acylhydrolase, EC 3.1.1.8) refers to a family of at least 15 isozymes found in blood and many tissues of animals. In this assay, acetylcholine is used as the substrate, and a postcolumn reactor containing choline oxidase produces electrochemically active H2C>2 upon oxidation of choline. 

Nine of the remaining patients had dibucaine numbers (measured by the choline oxidase procedure) characteristic of the EyEy genotype and the sera of six had no activity with succinylcholine (Section 3.2). These 15 patients had cholinesterases whose properties appear to be quite different from those of any other variants that have been reported, with one possible exception. The six patients whose serum exhibited no activity with succinylcholine but did show the usual level of activity with benzoylcholine, represent a probable new phenotype. The nine patients who had DN values characteristic of the usual phenotype when using benzoylcholine as substrate but DN values characteristic of the atypical enzyme when using succinylcholine, must also be classified as representing... 

Cholinesterase. Cholinesterase can be assayed by determining the choline liberated in the enzymatic reaction by using immobilized choline oxidase. Further, the direct electrochemical registration of thiocholine iodide, the product of the cholinesterase-catalyzed hydrolysis of butyrylthiocholine iodide, has been used [384]. The Glukometer has been adapted to this reaction system by polarizing the platinum electrode to 470 mV versus an Agl electrode in 0.1 M potassium iodide solution. The formation of thiocholine iodide causes an increase in the oxidation current. After a transient phase of about 20 s the reaction rate becomes constant. In the kinetic mode a constant measuring value proportional to the reaction rate is obtained. A... 

Urease/glutamic dehydrogenase Acetyl cholinesterase/choline oxidase... 

Organophosphorus compounds are significant major environmental pollutants due to their intensive use as pesticides. The modem techniques based on inhibition of cholinesterase enzyme activity are discussed. Potentiometric electrodes based on detection of cholinesterase inhibition by analytes have been developed. The detection of cholinesterase activity is based on the novel pindple of molecular transduction. Immobilized peroxidase acting as the molecular transducer, catalyzes the electroreduction of hydrogen peroxide by direct (mediatorless) electron transfer. The sensing element consists of a carbon based electrode containing an assembly of co-immobilized enzymes cholinesterase, choline oxidase and peroxidase. 

Cremisini, C., Sario, S., Mela, J., et al, 1995. Evaluation of the use of free and immobilised acetylcholinesterase for paraoxon detection with an ampero-metric choline oxidase based biosensor. Analyt. Chim. Acta 311, 273-280. Darvesh, S., Walsh, R., Kumar, R., et al, 2003. Inhibition of human cholinesterases by drugs used to treat Alzheimer s disease. Alzheimer Dis. Assoc. Disord. 17,117-126. 

When enzyme sensors are combined with FIA they have applications in medicine and the food produce industry. For example, FIA has been combined with the glucose oxidase electrode to determine glucose in blood [270], with the choline oxidase electrode for the determination of cholinesterase in serum [271], and with a bienzyme electrode that uses choline oxidase and phospholipase for the determination of phospholipids in serum [272]. The technique has also been used with an alcohol oxidase electrode to determine alcohol in drinks (for example, beers) [273], or with a glucose oxidase electrode to determine glucose [274] in various foodstuffs [275] or in fermentation processes [276]. 

Amperometric determination of pesticides based on inhibition of cholinesterases can be also carried out in bi-enzymatic systems with an additional enzymatic step involving choline oxidase. During the oxidation of choline by this enzyme oxygen is consumed and hydrogen peroxide is produced (see Figs. 13.1 and 13.3) hence, the change of the concentration of one of these species can be the basis for the amperometric response. 

Most studies have focused on amperometric glucose sensors based on GOx or GOx/ peroxidase [168-182]. However, a wide variety of other enzymes, including peroxidase, tyrosinase, choline oxidase, sarcosine oxidase, cholesterol oxidase, xanthine oxidase, glutamate oxidase, glutamate dehydrogenase, nitrate reductase, cholinesterase, cholesterol esterase, uricase, urease, creatinase, and creatininase, have also been employed for bioelectrosensor construction [183-203]. Representative examples are outlined in Table 2. 

A popular method of determination of cholinesterase activity is based on coupling a cholinesterase enzyme with a choline electrode (26-39). This coupling results in two consecutive enzyme reactions, first catalyzed by cholinesterase (equation 1), and second, catalyzed by chohne oxidase ... 

---