In enzymatic assay

What factors can be used to predetermine the quality and utility of a method An analyst must consider the following questions Do I need a proximate analytical method that will determine all the protein, or carbohydrate, or lipid, or nucleic acid in a biological material Or do I need to determine one specific chemical compound among the thousands of compounds found in a food Do I need to determine one or more physical properties of a food How do I obtain a representative sample What size sample should I collect How do I store my samples until analysis What is the precision (reproducibility) and accuracy of the method or what other compounds and conditions could interfere with the analysis How do I determine whether the results are correct, as well as the precision and accuracy of a method How do I know that my standard curves are correct What blanks, controls and internal standards must be used How do I convert instrumental values (such as absorbance) to molar concentrations How many times should I repeat the analysis And how do I report my results with appropriate standard deviation and to the correct number of significant digits Is a rate of change method (i.e., velocity as in enzymatic assays) or a static method (independent of time) needed ... 

Amperometry is most commonly employed in enzymatic assays in which hydrogen peroxide is one of the products. Hydrogen peroxide is oxidized at a constant... 

Eder AF, Dowdy YG, Gardiner JA, Wolf BA, Shaw LM. Serum lactate and lactate dehydrogenase in high concentrations interfere in enzymatic assay of ethylene glycol. Clin Chem 1996 42 1489-91. 

Because the enzyme substrate and the products are unstable, it is difficult to measure the disappearance of substrate or the formation of products as is usual in enzymatic assays. Routine assays for SOD usually employ an indirect assay in which one unit of enzyme activity is defined as the amount of enzyme that inhibits the reaction of 02 with the indicator by 50%. The most frequently used method for measuring SOD activity employs the xanthine/xanthine oxidase reaction for... 

NADH and NADPH, the respective reduced forms of NAD and NADP, are highly fluorescent hence, all NAD" "- and NADP -dependent reactions involved in enzymatic assays can be monitored fluorimetrically with a sensitivity higher than those of absorptiometric techniques by two or three orders of magnitude. Reactants must be used at much lower concentrations, and detection limits of 10 moll or even lower can be achieved. Numerous methods for enzyme determination involve the use of substrates that are transformed into highly fluorescent products. For instance, p-hydroxyphenyl-acetic acid has been used widely as a substrate for the determination of several oxidases such as glucose oxidase and xanthine oxidase. 

It should be noted that ICso alone is not a perfect parameter reflecting the binding properties of covalent inhibitors. However, using an identical scaffold and holding the exact same set of parameters in enzymatic assays make it an easily accessible way for a quick assessment of inhibitors. 

Overall, the implementation of lanthanide probes in chemical sensor technology is still in its initial stage. Up to now they have not found their way into commercialized sensor systems. Particularly, with respect to p02 and pH sensors, it cannot be foreseen that LLCs may displace established fluorescent indicators. Sensors for small molecules such as hydrogen peroxide, phosphate, or ATP can be useful in enzymatic assays in which the conversion of the substrate has to be monitored. In this case, the selectivity is provided by the enzyme involved. A concrete example is presented by means of a glucose sensor based on immobilized glucose oxidase and... 

In addition to the use of emittive acceptors to measure sensitized emission, various nonemitting compounds have also been used in assays where the proximity creates signal quenching. Those assays are mainly apphed in enzymatic assays where hydrolysis intermpts the proximity and reaction is followed by recovery of the signal. 

Fixed and variable volume pipettes find application in microbiology labs for preparation of dilutions as well as accurate dispensing of small (pL) volumes of reagents. Generally, fixed volume pipettes are used for routine laboratory purposes such as dilution, whereas variable volume pipettes are used in enzymatic assays requiring small-volume transfers. 

Aside from measuring absorbance/transmittance of soluble compounds, spectrophotometric and nephelometric methods have also been used to estimate particle (microbial) density in a suspension. In the microbiology laboratory, the spectrophotometer find most frequent application in enzymatic assays (e.g., malic or lactic acid) whereas nephelometers quantify haze (turbidity) in a sample. Both spectrophotometers and nephelometers measure the interaction of light with soluble compounds or particles (Section 14.7). 

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