Enzyme mixture composition, effect

Fumarase has been studied intensively with respect to the effects of pH changes and certain other environmental changes on enzyme activity. These effects will be considered in detail, as the principles involved apply to all enzymes. Changes in the composition of incubation mixtures influence the rate of enzyme-catalyzed reactions by altering the substrate or by modifying the enzyme. Even though effects caused by changes in pH may sometimes appear complicated, they can aU be... 

Chimeric enzymes constructed fi"om two different angiosperms (Panax ginseng, Araliaceae, and Arabidopsis thaliana, Brassicaceae) yielded mixtures of triterpenoids, p-amirin and lupeol, at a composition depending on the particular chimera methyl scrambling was observed for lupeol only (Kushiro 1999). A few differences in the amino acids at the active site are responsible for these effects. This implies that the high variety of plant triterpenoids owes more to chimeric enzymes than product-specific triterpene synthases. It was proposed that these chimeric enzymes act as multifunctional triterpene synthases (Kushiro 1999). 

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. 

Whether processes include biocatalysis followed by chemistry or vice versa, it would be advantageous to match the solvent composition, pH, and process intensities of both steps. In many cases the solution of choice may be to modify the enzyme to operate most effectively under conditions that favor the chemical transformation (i.e., in an organic solvent or an aqueous-organic solvent biphasic mixture). The engineering principles governing the design of such processes are... 

As with most heterogeneous catalysts, it is often difficult to characterize immobilized enzymes at a molecular level. Most immobilized preparations are often complex mixtures with a distribution of chemically modified protein species. The gross catalytic properties observed are a composite of those of a range of differentially modified individual proteins, often irregularly distributed within the sample. Mass transfer limitations and microenvironment effects further complicate characterization. 

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