In enzyme assays

Another reason is that xylo-oligosaccharides of defined structure are very important substrates that serve as model compounds for the optimization of hydrolytic processes and in enzymic assays. The enormous development... 

Extracellular PG activity was not detected in cultures on glucose, a similar situation to that of Fusarium moniliforme (18). In contrast, all our data confirm the presence of the protein and the mRNA of PG in non-inducing conditions our assays did reveal no differences between FORL PG growing on both conditions, regarding migration or other detectable characteristics that could justify the presence of the enzyme and its lack activity. It is posible that a very low concentration of the enzyme results in undetectable activity in enzyme assays. 

Occasionally, one can increase the Ae by utilizing alternative substrates. For example, 3-acetyl-NAD or thio-NAD can often be used with NAD -dependent dehydrogenases. Note however that an alternative substrate may change the kinetic mechanism, as compared to that observed with the naturally occurring substrate. Alternative substrates are of particular value when the normal substrate(s) and product(s) do not efficiently absorb UV or visible light. For example, many p-nitroaniline or p-nitrophenyl derivatives have proved to be quite useful in enzyme assays because they exhibit intense absorption around 410 nm. 

The majority of the many methods used to study the composition of equilibrium solutions of carbohydrates examine the mixture without separating the individual components. With the discovery that the anomeric forms of sugars could be readily separated by gas chromatography of their tri-methylsilyl ethers, a new approach to the problem was found. A protocol was developed for the direct gas chromatographic analysis of the amount of each anomer present in an aqueous solution. The protocol can be used on the micro scale and can be used in enzyme assays such as that for mutarotase. The method has been made more effective by combining gas chromatography with mass spectrometry. It is shown how mass spectral intensity ratios can be used to discriminate anomers one from another. The application of these methods to the study of complex mutarotations is discussed. 

A good source of information on the design and execution of enzyme assays. The initial chapter, by K.F. Tipton, provides an excellent discussion of the general principles involved in enzyme assays. Subsequent chapters deal with specific assay approaches. 

Stauffer, C.E. 1989. Peptide hydrolases. In Enzyme Assays for Food Scientists, pp. 133-161. VanNos-trand Reinhold, New York. 

Clark, J.B. 1992. Electrochemical assays The oxygen electrode. In Enzyme Assays A Practical Approach (R. Eisenthal and M.J. Danson, eds.) pp. 181-190. IRL Press, Oxford. 

Coumarins also have a C6-C3 skeleton, but they possess an oxygen heterocycle as part of the C3-unit. There are numerous coumarins, many of which play a role in disease and pest resistance, as well as UV-tolerance. The coumarin umbelliferone (1.21) is popular in enzyme assays. Umbelliferone esters can be used as a substrate for non-specific esterase enzyme assays and in fluorescent immunoassays (Jacks and Kircher, 1967). In order to quantify the enzyme activity of the popular reporter gene P-glucuronidase (GUS), plant extracts can be incubated with 4-methylumbelliferyl P-D-glucuronide (4-MUG 1.22), which upon hydrolysis... 

Generally, the nicotinamide coenzymes are not covalently bound to the enzyme. They are employed in enzyme assays and preparative applications by adding catalytical but optimized amounts, and they need to be recycled. For an economic process, an efficient regeneration method is a basic requirement. The necessary recycle number depends essentially on the value of the chiral product, generally the method should recycle the coenzyme 100-100,000 times ([42]). 

High-molecular-weight solid substrates such as hide powder azure, and cellulose, chitin, and agar stained with remazol brilliant blue R have been used in enzyme assays to investigate activities in extracts from sediments (Reichardt, 1986). This technique is one of the few means of examining the particle — dissolved transition in relationship to sedimentary enzyme activity, but the necessity of extracting enzymes from sediments complicates interpretation of the results, because extraction efficiency, as well as the... 

The cells on the paper disc are viable and may be used in autoradiographic studies. Alternatively, they may be lysed by freeze-thawing and incubated in enzyme assays. 

Assay (Taken from the Official Methods of Analysis, 16th edition, chapter 32, pp. 7-9, method number 991.43. 1995. AOAC INTERNATIONAL.) (Note Verify that all enzymes used in this procedure exhibit not less than 95% of their declared potencies using the tests given in Enzyme Assays, Appendix V.)... 

Use of NAD(P) in Enzyme Assays The reduced coenzymes have an absorption maximum at 340 nm, whereas the oxidized coenzymes do not. This is widely exploited to provide sensitive and specific methods for determining a variety of analytes using purified NAD (P)-linked enzymes and following the change in absorption at 340 nm as the coenzyme is either reduced or oxidized by the substrate. 

In enzyme assays, methylviologen is often used as an artificial electron acceptor. 

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