Metabolic biosensors

E.I. Iwuoha, S. Joseph, Z. Zhang, M.R. Smyth, U. Fuhr, and P.R. Ortiz de Montellano, Drug metabolism biosensors electrochemical reactivities of cytochrome CYP101 immobilised in synthetic vesicular systems. J. Pharm. Biom. Anal. 17, 1101-1110 (1998). 

Ehtylbenzene and 3-xylene (log Kow values of 3.15 and 3.20, respectively) were removed because they were outliers (R2 = 0.73 when included in the analysis) (data not shown). Their removal can be justified by the fact that for the highest concentrations tested, these compounds were found to be toxic to a luminescent metabolic biosensor of P. putida FI, and it may be assumed that they were toxic to P. putida TVA8 accordingly. As a consequence of the removal of these data, there is a significant gap of chemicals for octanol-water partition coefficients between 2.73 and 4.90. 

Zhang LR, Xing D,. Wang JS. A non-invasive and real-time monitoring of the regulation of photosynthetic metabolism biosensor based on measurement of delayed fluorescence in vivo. Sensors 2007 7 52-66. 

New developments in this area include uric acid sensors based on the mediation of urate oxidase by a novel redox polymer, poly(N-methyl-o-phenylenediamine) [145], and by the freely diffusing mediator 1-methoxy-5-methylphenazinium [146], continued research on the direct amperometric detection of NADH [147] and the use of redox mediators [148] for dehydrogenase enzymes, to allow practical sensors that exploit this large class of enzymes, and the use of cytochrome P450-modified glassy carbon electrodes as drug metabolism biosensors [149]. 

Metabolic biosensors are based on the specific recognition of some enzyme substrate and its subsequent chemical conversion to the corresponding product(s). The biocatalytic reaction itself accomplishes specific binding between the active site of... 

Hartmann T, Ober D (2000) Biosynthesis and Metabolism of Pyrrolizidine Alkaloids in Plants and Specialized Insect Herbivores. 209. 207-243 Haseley SR, Kamerling JP, Vliegenthart JFG (2002) Unravelling Carbohydrate Interactions with Biosensors Using Surface Plasmon Resonance (SPR) Detection. 218 93-114... 

Besides catalyzing styrene and benzaldehyde, CYP enzymes play an important role in the metabolism of endogenous compounds as well as in pharmacokinetics and toxicokinetics. Joseph [228] developed a biosensor with human CYP3A4 as a novel drugscreening tool. It was constructed by assembling enzyme films on Au electrodes by alternate adsorption of a layer of CYP3A4 on top of a layer of PDDA. The biosensor was applied to detect verapamil, midazolam, quinidine, and progesterone. 

A biosensor was designed where a dehydrogenase and an enlarged coenzyme are confined behind an ultrafiltration membrane. The amino acid is determined indirectly, by measuring the fluorescence of the reduced coenzyme (kex 360 nm, kfl 460 nm) produced in reaction 22, with the aid of an optical fiber. The coenzyme is regenerated with pyruvate in a subsequent step, as shown in reaction 23. This biosensor was proposed for determination of L-alanine and L-phenylalanine for monitoring of various metabolic diseases and for dietary management363. 

For these reasons, microbial sensors are less suitable for the determination of individual analytes. However, some practical apphcations for biosensors based on enzymes or antibodies for the specific determination of environmentally relevant compounds can be expected soon [11]. Furthermore, in some cases defined specific metabolic pathways in microorganisms are used, leading to microbial sensors for more selective analysis for those environmental pollutants which cannot be measured by the use of simple enzyme reactions, e.g., aromatic compounds and heavy metals. In this context it is also important to mention the aspect of bio availability, a parameter which is included by the measuring procedure of microbial sensors as an integral effect. 

Differences between both tests result from the different test principles. Biosensors use either a pure culture of microbes or a defined combination of several species of microorganisms with a fixed metabolic state, whereas for the conventional method an undefined bacterial population derived from activated sludge is used. In Sect. 3.2.1.3 it is shown that this obstacle can at least partly be overcome by the selection of suitable microorgaiusms for the BOD-sensor design. 

The improvement of the correlation of sensorBOD and BODj can also be achieved by incubating the biosensor for some hours in this wastewater sample, which has to be measured [53]. This allows the induction of all of the microorganisms required metabolic degradation systems [65]. As shown in Table 5, preincubated microbial sensors and the conventional BODj method revealed similar results. 

Measuring the increased oxygen resulting from the inhibition of respiration allows one to register the toxicity of wastewater. Toxic substances cause a reduction of the metabolic activity of the microorganisms used in the biosensor, resulting in a decrease of respiration. 

Konig et al. [80-84] demonstrated that microbial sensors are suitable for the summary quantification of nitrifiable compounds (see also Sect. 3.3.1) as well as for the detection of nitrification inhibiting effects. Such biosensors, which contain a mixed population of the nitrifying bacteria Nitrosomonas sp. and Nitrobacter sp., exhibit a specific supplementary metabolic capacity. This enables the amperometric determination of ammonia according the following scheme of nitrification ... 

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