Enzymes practical information from

Turnover numbers are a particularly dramatic illustration of the efficiency of enzymatic catalysis. Catalase is an example of a particularly efficient enzyme. In Section 6.1, we encountered catalase in its role in converting hydrogen peroxide to water and oxygen. As Table 6.2 indicates, it can transform 40 million moles of substrate to product every second. The following Biochemical Connections box describes some practical information available from the kinetic parameters we have discussed in this section. 

Determinations of Km and Ki have become routine in enzyme chemistry because of the theoretical and practical information derived from these values. From the theoretical point of view, the affinity of an enzyme for a substrate is important in determining the nature of the bonds between them, especially when the relative affinities for a variety of related structures (both substrates and inhibitors) can be determined. Variations in Km with changes in the physical environment give additional information about the nature of the binding forces. Practically, the Km permits decisions to be made about the concentrations required to obtain desired rates of reaction, the relative success of different enzymes that use the same substrate, the feasibility of using an enzyme assay for analysis of substrate at given concentrations, the ability of an enzyme to pull another reaction by removing a product, the relative rates of reaction when two substrates are present, and the relative effects of competitive inhibitors. 

Practically all toxicokinetic properties reported are based on the results from acute exposure studies. Generally, no information was available regarding intermediate or chronic exposure to methyl parathion. Because methyl parathion is an enzyme inhibitor, the kinetics of metabolism during chronic exposure could differ from those seen during acute exposure. Similarly, excretion kinetics may differ with time. Thus, additional studies on the distribution, metabolism, and excretion of methyl parathion and its toxic metabolite, methyl paraoxon, during intermediate and chronic exposure are needed to assess the potential for toxicity following longer-duration exposures. 

A solution to the problem of introns is to isolate mRNA extracted from the human pancreas cells that make insulin. These cells are rich in insulin mRNA from which introns have already been spliced out. Using the enzyme reverse transcriptase it is possible to convert this spliced mRNA into a DNA copy. This copy DNA (cDNA), which carries the uninterrupted genetic information for insulin can be cloned. Although yeast cells (Saccharomyces) can splice out introns it is normal practice to eliminate them anyway by cDNA cloning. 

In summary, the recent developments on fluorinase enzyme research have explored the structure, mechanism and substrate specificity in some detail. Progress has been made at the genetic level which is beginning to inform our understanding of the organisation of the fluorometabolite pathway within S. cattleya although much more remains to be uncovered here. In terms of applications of this enzyme, its utility as a synthesis tool for the incorporation of the fluorine-18 isotope from [ F]-fluoride ion has proven practical, and there may be a role for the fluorinase in the synthesis of some PET ligands. 

Antibody catalysts have been created for many classes of reaction [2, 3], In addition to simple model reactions, transformations for which natural enzymes are unavailable have been successfully promoted. From a practical standpoint, the exacting control of reaction pathway and absolute stereochemistry that can be achieved with these agents is particularly notable. Because genetic and structural information is generally readily available, these catalysts are also valuable tools for studying how natural enzymes work and evolve. 

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