Enzymes abiotic

However, the results obtained in recent years have also established that the structural characteristics of the established dendrimer systems, such as the absence of a well-defined secondary structure, have limited the development of efficient abiotic enzyme mimics based on dendrimers. To achieve this ambitious goal, more efforts in dendrimer synthesis will be necessary. The use of dendritic catalysts in biphasic solvent systems has only just begun and appears to be a particularly fruitful field for further developments. These utilitarian aspects aside, it is the aesthetic attraction of these topologically highly regular macromolecules that continues to fascinate those working in the field of dendrimer catalysis. 

Enzymes released into outside environment and not attached to the producer. These are often referred to as exoenzymes or abiotic enzymes. 

Both the active enzyme, the heat-inactivated enzyme from Sulfurospirillum (Dehalos-pirillum) multivorans, and cyanocobalamin are capable of dehalogenating haloacetates (Nenmann et al. 2002), and the rate of abiotic dehalogenation depends on the catalyst that is nsed. 

Abiotic spoilage is produced by different physical and chemical changes such as hydrolytic action of enzymes, oxidation of fats, breakdown of proteins, and a browning reaction between proteins and sugars. However, in this chapter we focus on microbial deterioration and their effects on bioactive compounds. 

This process was extended to the phosphorylation of various substrates, in particular to the synthesis of ATP from ADP in mixed solvent [5.62a] and in aqueous solution in the presence of Mg2, probably via formation of a ternary catalytic species 83 [5.62b]. The latter abiotic ATP generating system has been coupled to sets of ATP consuming enzymes resulting in the production of NADH by a combined artificial/natural enzymatic process (Fig. 9) [5.63]. 

The systems described in this chapter possess properties that define supramolecular reactivity and catalysis substrate recognition, reaction within the supermolecule, rate acceleration, inhibition by competitively bound species, structural and chiral selectivity, and catalytic turnover. Many other types of processes may be imagined. In particular, the transacylation reactions mentioned above operate on activated esters as substrates, but the hydrolysis of unactivated esters and especially of amides under biological conditions, presents a challenge [5.77] that chemistry has met in enzymes but not yet in abiotic supramolecular catalysts. However, metal complexes have been found to activate markedly amide hydrolysis [5.48, 5.58a]. Of great interest is the development of supramolecular catalysts performing synthetic... 

Supramolecular catalysts are by nature abiotic chemical reagents that may perform the same overall processes as enzymes, without following the detailed pathway by which the enzymes actually effect them or under conditions in which enzymes do not operate. Furthermore and most significantly, this chemistry may develop systems realizing processes that enzymes do not perform while displaying comparable high efficiencies and selectivities. 

Allosteric effects play a major role in biology, for instance in the conformational changes induced by the binding of an effector and regulating the activity of an enzyme [9.14a] they have also been studied in synthetic receptors [8.201, 8.211, 9.14b, c]. Similarly, cooperativity, a thermodynamically well defined process [9.15a], is displayed by a number of biological species as well as by abiotic ones [8.70a, 8.201, 9.15b-d] (see also Section 9.3.1, [9.64, 9.65]), in particular in organized media such as polymer solutions or gels [7.8cd, 8.290, 8.292]. 

Biooxidation of chiral sulfides was initially investigated in the 1960s, especially through the pioneering work of Henbest et al. [101]. Since then, many developments have been reported and are summarized in reviews [102,103], It would be helpful to reveal some structural or mechanistic details of enzymes involved in theoxidation processes. Biotransformations are also of great current interest for the preparation of chiral sulfoxides, which are useful as synthetic intermediates and chiral auxiliaries. Because extensive review of these transformations is beyond the scope of this chapter, only highlights are discussed in comparison with the abiotic enantioselective oxidations described earlier. Biooxidations by microorganisms and by isolated enzymes are discussed in Sections 6C.12.1. and 6C.12.2. 

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