Peptides sulfhydryl containing

Figure 19.19 shows a plot of the results of such an assay done to determine the maleimide content of activated BSA. This particular assay used 2-mercaptoethanol which is relatively unaffected by metal-catalyzed oxidation. For the use of cysteine or cysteine-containing peptides in the assay, however, the addition of EDTA is required to prevent disulfide formation. Without the presence of EDTA at 0.1 M, the metal contamination of some proteins (especially serum proteins such as BSA) is so great that disulfide formation proceeds preferential to maleimide coupling. Figure 19.20 shows a similar assay for maleimide-activated BSA using the more innocuous cysteine as the sulfhydryl-containing compound. 

Protocol for the Coupling of Peptide Haptens Containing Sulfhydryl Groups to Liposomal Vesicles... 

Dissolve a sulfhydryl-containing peptide hapten at a concentration of 25 pmol/ml in degassed, nitrogen-purged lOmM HEPES, 0.15M NaCl, pH 7.0. Add the peptide solution to the liposome suspension at a molar ratio necessary to obtain at least a 5 1 excess of thiol groups to the amount of maleimide groups present (as MPB-DPPE). 

Other methods that are related to affinity chromatography include hydrophobic interaction chromatography and thiophilic adsorption. The former is based on the interactions of proteins, peptides, and nucleic acids with short nonpolar chains on a support. This was first described in 1972 [113,114] following work that examined the role of spacer arms on the nonspecific adsorption of affinity columns [114]. Thiophilic adsorption, also known as covalent or chemisorption chromatography, makes use of immobilized thiol groups for solute retention [115]. Applications of this method include the analysis of sulfhydryl-containing peptides or proteins and mercurated polynucleotides [116]. 

Table V summarizes the reduction activity of acetylene with the Co(II)-complex catalysts of various sulfhydryl-containing peptides. Of interest is the high activity of the sulfhydryl- and imidazole-containing peptides such as N-mercaptoacetyl-L-histidine and N-mercaptoacetyl-DL-histidyl-DL-histidine. In addition, the effect of amino-acid residues on the reduction of acetylene with these Co(II) complexes decreases in the order histidine > glycine > cysteine > tryptophan.

A comparison of the structures of penicillin and Dalanyl-Dalanine (cf. structures 41 and 42) shows that there is a great deal of similarity between the two molecules. Penicillin is essentially an acylated cyclic dipeptide of Dcysteine and Dvaline (84). As such, it contains a peptide bond, that of the /3-lactam ring, that can acylate the enzyme. Labeling studies of the peptidoglycan transpeptidase of Bacillus subtilis indicate that radioactive penicillin reacts with a sulfhydryl group of a cysteine residue of the enzyme (86). 

Some proteins contain covalent disulfide (S— S) bonds that link the sulfhydryl groups of cysteinyl residues. Formation of disulfide bonds involves oxidation of the cysteinyl sulfhydryl groups and requires oxygen. Intrapolypeptide disulfide bonds further enhance the stability of the folded conformation of a peptide, while interpolypeptide disulfide bonds stabilize the quaternary structure of certain oligomeric proteins. 

For small molecules containing sulfhydryls or for low-molecular-weight peptides containing cysteine residues, modification may proceed without deforming agents. However, for intact proteins containing both disulfides and free sulfhydryls, a denaturant and a disulfide reducing... 

FIGURE 5.22 (A) Reaction of an Fmoc-amino acid with 2-chlorotrityl chloride resin.56 The ester bond formed is cleavable by the mild acid, which does not affect tert-butyl-based protectors. (B) Generation of a protected peptide containing cystine by detachment of a chain, deprotection of cysteine residues, and oxidation of the sulfhydryls by the reagent containing iodine. The cations produced are trapped by CF3CH2OH. 

THE SULFHYDRYL GROUP OF CYSTEINE AND THE SYNTHESIS OF PEPTIDES CONTAINING CYSTINE... 

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