Enzymatically controlled

The tetramerization of suitable monopyrroles is one of the simplest and most effective approaches to prepare porphyrins (see Section 1.1.1.1.). This approach, which is best carried out with a-(hydroxymethyl)- or ot-(aminomethyl)pyrroles, can be designated as a biomimetic synthesis because nature also uses the x-(aminomethyl)pyrrole porphobilinogen to produce uroporphyrinogen III. the key intermediate in the biosynthesis of all kinds of naturally occurring porphyrins, hydroporphyrins and corrins. The only restriction of this tetramerization method is the fact that tnonopyrroles with different -substituents form a mixture of four constitutionally isomeric porphyrins named as porphyrins I, II, III, and IV. In the porphyrin biosynthesis starting from porphobilinogen, which has an acetic acid and a propionic acid side chain in the y6-positions, this tetramerization is enzymatically controlled so that only the type III constitutional isomer is formed. 

Worldwide suppliers with bioengineering capabilities are displacing established polymers with cost-effective and higher performing plastics. An explosion of novel polymers has been made by enzymatic control. The use of enzymes for polymerization has drastically altered the landscape of polymer chemistry. Processors can request specific properties for each application as opposed to the usual making do with what is available. The supplier can deliver to the processor desired properties requested. 

Polysaccharide synthesis is under enzymatic control, but does not occur from a template as in protein synthesis. For this reason, each molecule of a particular polysaccharide will have its own unique molecular weight. The molecular weight of a carbohydrate polymer is usually expressed as an average. Starch or cellulose chains, for example, may vary by several hundred thousand in their molecular weights between individual molecules. For an excellent review of carbohydrate chemistry, see Binkley (1988). 

Needless to say, there is a definite possibility that, if reactions as just described participate in the transformations of polyuronide polysaccharides, enzymatic control of these may exist by systems leading to the oxidation of ascorbic acid or producing peroxide-type intermediaries. 

Syntheses of both enantiomers of 157 are depicted in Fig. 8. Both approaches involve enzymatically controlled reactions during asymmetric syntheses. 

In contrast to Mori s synthesis, Pawar and Chattapadhyay used enzymatically controlled enantiomeric separation as the final step [300]. Butanone H was converted into 3-methylpent-l-en-3-ol I. Reaction with trimethyl orthoacetate and subsequent Claisen-orthoester rearrangement yielded ethyl (E)-5-methyl-hept-4-enoate K. Transformation of K into the aldehyde L, followed by reaction with ethylmagnesium bromide furnished racemic ( )-7-methylnon-6-ene-3-ol M. Its enzyme-catalysed enantioselective transesterification using vinylacetate and lipase from Penicillium or Pseudomonas directly afforded 157, while its enantiomer was obtained from the separated alcohol by standard acetylation. 

In nature, polycondensations of trifunctional monomers having two different functional groups occur under enzymatic control, resulting in tree-shaped, highly branched, but still soluble, macromolecules. 

Berger R, Libby WE. 1969. Equilibration of atmospheric carbon dioxide with sea water possible enzymatic control of the arte. Science 164 1395-1398. 

B. C. Goodwin, Oscillatory behavior in enzymatic control processes. Adv. Enzyme Regul. 3, 425-A38 (1965). 

It remains to be seen whether pan-HDAC inhibition is a prerequisite for clinical efficacy, or whether more subtype-specific HDAC inhibition offers clinical advantages in relation to efficacy and/or toxicity. It should be understood however that the current state of the art suggests that chromatin remodeling is not the only way in which HDACi exert their antitumor effects. As more and more evidence indicates that HDACs not only play a central role in the epigenetic status of chromatin, but are also involved in other levels of enzymatic control, their ability to act on multiple molecular pathways only adds to their multi-targeting properties. 

Some natural polymers such as cotton, slik, and cellulose have the extended-chain morphology, but their morphologies are determined by enzymatically controlled synthesis and crystallization processes. Extended-chain morphology is obtained in some synthetic... 

During the last two decades, chemists have become increasingly focused on how molecules interact, i.e. on supramolecular chemistry. Dynamic intermolecular processes provide opportunities for incorporation of control, adaptation and function in man-made materials, as observed in living systems. In biology, these processes are tightly controlled by the catalytic action of enzymes. In this chapter, we focus on enzymatically controlled supramolecular polymerisation, whereby self-recognising molecular building blocks assemble to form extended onedimensional (ID) structures, or supramolecular polymers, with unique adaptive features. 

Yang ZM, Liang GL, Xu B (2007) Enzymatic control of the self-assembly of small molecules a new way to generate supramolecular hydrogels. Soft Matter 3 515-520... 

Gap junction conductance (gj) of neonatal rat heart cells varies with temperature (37 °C, 48.3 nS 14 °C, 21.4 nS -2°C, 17.5 nS) [Bukauskas and Weingart, 1993] so that gj has been assumed to be at least in part enzymatically controlled. Several protein kinases are known to be involved in the regulation of the gap junction channels. However, the situation is rather complicated since the same protein kinase may enhance or reduce gap junctional conductance in different tissues or in different species. Thus, generalizations should be avoided and the specific condition has to be taken into account. One of the first to be described was protein kinase A (PKA), the cAMP-dependent protein kinase, which can enhance junctional conductance in hepatocytes coupled via Cx32 and Cx26 [Saez et al., 1986, 1990]. Similarly, an increase in junctional conduc-... 

Kirsch-De-Mesmaeker A, Lecomte J-P, Kelly JM (1996) Photoreactions of Metal Complexes with DNA, Especially Those Involving a Primary Photo-Electron Transfer. 177 25-76 Kirschning A, Bechthold A F-W, Rohr J (1997) Chemical and Biochemical Aspects of Deoxy-sugars and Deoxysugar Oligosaccharides. 188 1 - 84 Kitazume T.Yamazaki T (1997) Enzymatically Controlled Reactions of Organofluorine Compounds. 193 91 -130... 

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