Alkylation of sulfhydryl group

IgM can be separated into its H and L chains by the usual methods of reduction in neutral buffer, alkylation of sulfhydryl groups, and gel filtration in dilute acetic or propionic acid (114,115). The L chain peak contains J chains, which can be separated from L chains by virtue of their high anodal electrophoretic mobility. 

Half-molecules are prepared from rabbit IgG by taking advantage of two properties of the molecule. First, the disulfide bond joining the two H chains (H-H bond) is more labile than the H-L bonds and, in fact, is the most labile disulfide bond in the molecule in the presence of 0.01 M 2-mercaptoethanol nearly aU H-H disulfide bonds, but very few H-L bonds, are reduced (56). Second, the noncovalent forces joining the two H chains are weaker than those linking H and L chains. Thus, even if all interchain disulfide bonds are reduced and alkylated, and the molecule is then exposed to HCl solution at pH 2.5, half-molecules, rather than free H and L chains, are liberated because the noncovalent interactions between H and L chains are not disrupted (56). (Separation of H from L chains requires more drastic dissociating conditions.) In practice, then, half-molecules are produced by reduction with 0.01 M to 0.02 M 2-mercaptoethanol, followed by alkylation of sulfhydryl groups and exposure to HCl-NaCl, pH 2.5 (54,55). The separation can be monitored in the... 

As seen in Figure 1, the organo sulfur compounds are methylated at the boiling point (90°C) of dimethyl carbonate, whereas methylation (or alkylation with other alkyl groups) of other functional groups requites higher temperatures. This has resulted in the selective methylation of sulfhydryl groups of compounds that contain other substituents that can be alkylated. The other substituents can then be alkylated at elevated temperatures (63). 

Castro, J.A. Effects of alkylating agents on human plasma cholinesterase The role of sulfhydryl groups In its active center. Biochem. Pharmacol. 17 295-303, 1968. 

The 2-chloroacetanilides (Figure 2.22) are also suggested to inhibit cell division in susceptible weeds. These compounds have found a major commercial market for the pre-emergence control of grass and some small seeded broad-leaved weeds in crops such as maize and soybean. It is likely that 2-chloroacetanilides also alkylate the sulfhydryl groups of certain essential plant enzymes. 

Examination of the three-dimensional structure of papain (Lab Quip) indicated that because of the extended groove present in the vicinity of the active site residue Cys-25, it should be feasible to alkylate the sulfhydryl group with a coenzyme analog, still permitting the binding of potential substrates. 

Because cysteine residues are prone to autooxidation, proteins that contain disulfide bonds or free sulfhydryl groups must be subjected to reduction-alkylation process prior to cleavage. Alkylation converts sulfhydryl groups to stable derivatives. Also, during the reduction-alkylation procedure, the three-dimensional structure of proteins is disrupted to allow more cleavage sites to be accessible. Proteins are first reduced by treatment with 2-mercaptoethanol or dithiothreitol to convert disulfide bonds to free sulfhydryl group ... 

Chloroacetol phosphate alkylates the sulfhydryl group. ) The reaction mixture was cooled in an ice bath and then treated with a portion of the same stock solution of sodium [ Hjborohydride that was used in the reduction of the modified carboxylase (see above). The final borohydride concentration in the reaction mixture was 0.1 M. After 1 hr the mixture was acidified to pH 2.0 with 1 N HCl and chromatographed on a column (1.2 X 22 cm) of Dowex 50 (H ) equilibrated and eluted with 50 mAf HCl. The concentration of the glutathione derivative in the peak fraction was determined with the amino acid analyzer the radioactivity in the same fraction was also determined, thereby providing the specific radioactivity of the [ H] borohydride. 

Figure 1.10 Sulfhydryl groups may undergo a number of additional reactions, including acylation and alkylation. Thiols also may participate in redox reactions, which generate reversible disulfide linkages.

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. 

PROTECTION OF CARBOXYL, HYDROXYL, AND SULFHYDRYL GROUPS BY TFRT-BUTYLATION AND ALKYLATION... 

The alkylating agents can transfer an alkyl radical to a suitable receptor site. Alkylation of DNA within the nucleus represent the major interactions which will lead to cell death. These agents react chemically with sulfhydryl, carboxyl, amino and phosphate groups of other cellular nucleophiles in the cells which make them unavailable for the normal metabolic reactions. Alkylating agents react with nucleic acid and inhibit... 

As a class, the alkylating agents exert their cytotoxic effects via transfer of their alkyl groups to various cellular constituents. Alkylations of DNA within the nucleus probably represent the major interactions that lead to cell death. However, these drugs react chemically with sulfhydryl, amino, hydroxyl, carboxyl, and phosphate groups of other cellular nucleophiles as well. The general mechanism of action of these drugs... 

In addition to the alkylation with iodoacetate (Eq. 3-24), sulfhydryl groups can react with N-ethylmale-imide (Eq. 3-39).281 This reaction blocks the SH groups irreversibly and has often been used in attempts to establish whether or not a thiol group plays a role in the functioning of a protein. Loss of function in the... 

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