Protein, acetylated sulfhydryl group

To deprotect the acetylated sulfhydryl group of SAMSA-modified proteins, add 100 pi of 0.5 M hydroxylamine hydrochloride in 50 mM sodium phosphate, 25 mM EDTA, pH 7.5, to each ml of protein solution. 

Deprotect the acetylated sulfhydryl groups on the SATA-modified protein according to the following protocol ... 

We can descnbe the major elements of fatty acid biosynthesis by considering the for mation of butanoic acid from two molecules of acetyl coenzyme A The machinery responsible for accomplishing this conversion is a complex of enzymes known as fatty acid synthetase Certain portions of this complex referred to as acyl carrier protein (ACP), bear a side chain that is structurally similar to coenzyme A An important early step m fatty acid biosynthesis is the transfer of the acetyl group from a molecule of acetyl coenzyme A to the sulfhydryl group of acyl carrier protein... 

Figure 1.63 Deprotection with hydroxylamine of the acetylated thiol of SATA-modified proteins yields a free sulfhydryl group.

Figure 1.68 N-Acetyl homocysteine thiolactone spontaneously reacts with amine groups on proteins to create sulfhydryl groups.

Figure 1.69 SAMSA is an anhydride compound containing a protected thiol. Reaction with protein amine groups yields amide bond linkages. Deprotection of the acetylated thiol produces free sulfhydryl groups for conjugation.

SAMSA-fluorescein, 5- [2(and 3)-5-(acetylmercapto)-succinoyl]amino fluorescein, is a fluorescent probe containing a protected sulfhydryl group. In its protected state, the compound is unre-active. The acetyl-protecting group can be removed by treatment with dilute NaOH at pH 10.0 (Figure 9.9). The resulting free sulfhydryl derivative can be used to label thiol-reactive crosslinkers or to couple with sulfhydryl residues on proteins and other molecules. After activating... 

Figure 8-2. Pathway for synthesis of palmitate by the fatty acid synthase (FAS) complex. Schematic representation of a single cycle adding two carbons to the growing acyl chain. Formation of the initial acetyl thioester with a cysteine residue of the enzyme preceded the first step shown. Acyl carrier protein (ACP) is a component of the FAS complex that carries the malonate covalently attached to a sulfhydryl group on its phosphopantatheine coenzyme (-SH in the scheme).

We have previously reviewed some of the evidence for conformational changes induced by ligands, including the protection by substrate against dinitrophenylation of sulfhydryl groups and by both substrate and AMP against acetylation of specific tyrosine residues. The pK values for some tyrosine residues in the protein may be shifted by more than one pH unit on addition of the substrate (see above). The addition of AMP will also induce small changes in the ionization constants for the tyrosine residues with the lowest p.K values (40). 

Chemical modification of soybean agglutinin by acetylation of its amino groups resulted in little loss of agglutinating activity, whereas the protein was quite sensitive to modification of its tyrosyl residues.547 Failure of the protein to react with 2-iodoacetamide or p-(chloro-mercuri)benzoate in 6 M urea confirmed that it was devoid of sulfhydryl groups. A metalloprotein containing151 Ca2+ and Mn2+, the soybean lectin is inactivated by Al3+, Fe3+, and Pb2+, whereas Mn2+, Ba2+, Mg2+, Ag+, Li+, and K+ are without effect.532... 

An example of a popular pharmaceutical with a toxic metabolite is acetaminophen (2, 3). A portion of the acetaminophen metabolized in the liver is converted to a reactive intermediate/ N-acetyl-p-benzoquinoneimine (NAPQI)/ which is an excellent substrate for nucleophilic attack by free sulfhydryl groups in proteinS/ as shown in Scheme 11.4. By substituting a high concentration of an alternative... 

Thiols are characterized by the sulfhydryl group (—SH). The amino acid cysteine is a thiol that is extremely important for maintaining the correct shapes of proteins. Coenzyme A is a thiol that serves as a "carrier" of acetyl groups in biochemical reactions. 

First, the KE2 antibody is thiolated using iV-succinimidyl-S-acetyl thioacetate in dimethyl strlfoxide. The succinimide group is coupled to the primary amines on the protein (antibody) which leads to the formation of covalent amide bonds with the loss of hydroxy succinimide. The sulfhydryl group is thus protected. The deprotection, through deacetylation, is carried out using EDTA and hydroxyl... 

Thus, depending on the pH of the reaction, sulfhydryl groups of cysteine react about 34 to 5000 times faster than the e-amino groups of lysine with vinyl compounds such as N-acetyl dehydroalanine methyl ester (Friedman and Wall, 1964 Friedman et al., 1965 Cavins and Friedman, 1967 Snow et al., 1976). Therefore, by adding thiols such as cysteine it may be possible to prevent the formation of dehydroalanine residues during alkali-treatment of proteins. 

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