Thioester formation

A superspiral consisting of two spirals (coiled coil), known as the leucine zip, is formed in this sequence via dimerisation. The condensation reaction, carried out in the aqueous phase, involves two peptide fragments which contain 15 and 17 amino acid residues respectively. Activation takes place via thioester formation (see Sect. 5.3.1). The ligation to a complete GCN4 matrix gives a new 32 amino acid peptide, which can itself serve as a matrix. The autocatalytic reaction exhibits a parabolic increase in the peptide concentration (caused by product inhibition see Section 6.4). 

In the latter case, electron uptake occurs after decarboxylation of the ketoacid via Fe3+, which is able to take up electrons in strongly oxidized regions of the black-band iron sediments. Fe-ions act catalytically on the process of thioester formation, which can then occur without the help of enzymes. Thus, it was solar UV irradiation which carried the prebiotic thioesters across the energy threshold. 

The H- and N-isoforms of Ras support the first (isoprenoid) hydrophobic modification by additional thioester formation with palmitoylic acids [18]. At physiological temperature (37°C) the dissociation of doubly modified lipo-peptides with an isoprenyl thioether and a palmitoyl thioester is very slow and characterized by half-times in the order of 50 h. Here, the relative effect of the carboxymethylation is significantly reduced. Palmitoyl groups with their C16 alkane chain length contribute more efficiently to membrane anchoring than the farnesyl modification. 

The second class of stable membrane anchoring motives does not rely on electrostatic interactions but supports the first (often isoprenoid) hydrophobic modification by additional thioester formation with fatty acids (eg. the H- and N-isoforms of Ras or in the a subunits of heterotrimeric G-proteins) or a second isoprenoid moiety (eg. Rab proteins).1331... 

Thioamide formation benzodiazepinone, 505 heteiodiazepinone, 621 phosphorus pentasulf ide, 323, 600 Thioazole formation, nitrile addition, 301 Thiocarbamate formation, 588 phenol, 95 rearrangement, 517 Thioenol ether formation, 185, 517 addition-elimination, 554 Thioester formation, mixed anhydride, 184 Thioether formation, 241, 300, 413, 416 alkylation, 586, 588 aromatic displacement, 416 Thiohydantoin formation, 293 Thiol interchange, benzothiazole formation, 422... 

Scheme 5.43 Stereoinversion of an -substituted carboxylic acid by combining an epimerization with an enantioselective thioester formation.

Monoclonal antibodies directed to the multienzyme Esyn were used to map the catalytic sites of the enzyme [29], The antibodies could be divided into three groups based on their influence on catalytic functions. Members of group one exclusively inhibited L-valine thioester formation, while members of group two... 

Scheme 36. The [NiS] mediated thioester formation from alkyl, CO, and thiols. [The alkyl and acyl complexes 38 and 39 were characterized by X-ray structure analysis for L = py (38) and L = PMe3 (39).]...

Scheme 36 represents the first example for a [NiS] mediated formation of thioesters from alkyl, CO, and thiol groups in a cyclic way. All intermediates shown in Scheme 37 could be intercepted and characterized by spectroscopic methods and X-ray structure analysis. They permit a detailed insight into the individual steps of thioester formation that may take place in an analogous way at the active site of CODH when acetyl-CoA is synthesized. 

Soraci, A.L. Benoit, E. In vitro fenoprophenyl-coenzyme a thioester formation interspecies variations. Chirality 1996, 7, 534-540. 

Explain the significance of thioester formation in the metabolic pathways involved in fatty acid and carbohydrate breakdown. 

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