Thioethers bonding

Cytochromes c (Cyt c) can be defined as electron- transfer proteins having one or several haem c groups, bound to the protein by one or, more commonly two, thioether bonds. Cyt c possesses a wide range of properties and function in a large number of different redox processes. 

The algal extract of P. aerugineum is blue, with maximum absorbance at a wavelength of 620 nm and a red fluorescence with maximum emission at 642 nm. The main phycobiliprotein, C-phycocyanin, is the same type of phycocyanin found in most Cyanobacteria. The chromophores are composed of phycocyanobilins, conjugated to an apoprotein via thioether bonds. 

Several extraction techniques have also been described that use enzymatic or chemical reactions to improve extraction efficiency. A technique that has been used to increase the overall recovery of the marker residue is enzymatic hydrolysis to convert specific phase II metabolites (glucuronides or sulfates) back into the parent residue. Cooper etal used a glucuronidase to increase 10-fold the concentration of chloramphenicol residues in incurred tissue. As an example of a chemical reaction, Moghaddam et al. used Raney nickel to reduce thioether bonds between benomyl and polar cellular components, and as a result achieved a substantially improved recovery over conventional solvent extraction. In choosing to use either of these approaches, thorough characterization of the metabolism in the tissue sample must be available. 

From the standpoint of modeling Type I copper proteins,4,5,59,60 a variety of imidazole-based ligands containing thioether sulfurs and imidazole groups have been synthesized.61,62 The structures and spectroscopic properties of their copper(II) complexes (51)-(53) and (55)-(60) were investigated.65,79-82 To characterize apical copper(II)-thioether bonding, the complex (51) was... 

Maleic acid imides (maleimides) are derivatives of the reaction of maleic anhydride and ammonia or primary amine compounds. The double bond of a maleimide may undergo an alkylation reaction with a sulfhydryl group to form a stable thioether bond (Chapter 2, Section 2.2). Maleic anhydride may presumably undergo the same reaction with cysteine residues and other sulfhydryl compounds. 

Sulfhydryl Compound Fluorobenzene Derivative Aryl Thioether Bond... 

Figure 4.18 BMH contains two maleimide groups specific for crosslinking sulfhydryl-containing molecules. The thioether bonds that are formed are stable.

Figure 5.7 SMPB may be used in a two-step procedure to conjugate an amine-containing molecule to a sulfhy-dryl compound, forming amide and thioether bonds, respectively.

Figure 5.10 SIAC reacts with an amine-containing compound to yield an amide bond derivative that is reactive toward thiol-containing molecules. Secondary reaction with a sulfhydryl group gives a stable thioether bond.

Figure 5.34 Benzophenone-4-maleimide can couple to thiol-containing molecules to form stable thioether bonds. Exposure of the benzophenone group to UV light causes transition to a triplet-state ketone of high reactivity for insertion into C—H or N—H bonds.

Figure 7.10 An NHS-PEG-maleimide compound can be used to functionalize dendrimers to provide a hydrophilic spacer terminating in thiol-reactive groups. Thiol-containing proteins then can be conjugated to this reactive intermediate to form covalent thioether bonds.

Figure 7.18 Amine-containing dendrimers can be activated with epibromohydrin to result in the formation of reactive epoxy groups on the dendrimer surface. This reactive intermediate then can be used to conjugate with thiol-containing proteins, such as thiolated alkaline phosphatase. The reaction results in the formation of a thioether bond.

The iodoacetyl group of both isomers reacts with sulfhydryls under slightly alkaline conditions to yield stable thioether linkages (Figure 9.7). They do not react with unreduced disulfides in cystine residues or with oxidized glutathione (Gorman et al., 1987). The thioether bonds will be hydrolyzed under conditions necessary for complete protein hydrolysis prior to amino acid analysis. 

Figure 9.8 Fluorescein-5-maleimide can be used to modify sulfhydryl groups, forming thioether bonds.

Figure 9.18 This iodoacetamide derivative of tetramethylrhodamine can be used to label sulfhydryl groups via thioether bond formation.

Figure 9.34 The long side chain of this BODIPY derivative contains a sulfhydryl-reactive iodoacetamide group that can couple to a thiol group to form a thioether bond.

Figure 9.42 Lucifer Yellow iodoacetamide can be used to label sulfhydryl-containing molecules, forming thioether bonds.

Figure 9.47 A maleimide-containing cyanine dye can be used to label thiol-containing molecules to form thioether bonds.

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