Selection cystein

Fig. 17.10. Schematic diagram of the ICAT strategy to proteomics. Samples are labelled, pooled and digested and undergo ICAT affinity chromatography to select cysteine-labelled peptides. Relative quantifications between proteins from both sample states are gained and tandem MS is performed to provide an identification.

A block copolymer effective as a controlled release agents of biologically active materials have been prepared. This agent consisted of ethylene oxide-propylene sulfide-ethylene oxide teipolymer that had been end-capped with a selected cysteine-containing peptide. These materials resist degradation prior to reaching their intended targets because they behave as multilamellar vesicles. 

X 10 (the assay s limit of detection). This high level of selectivity is to be expected as the incorporation of serine may lead to the formation of the potentially toxic analogue oxy-CoA, and raises the question as to the mechanism whereby this selectivity is achieved. One proposal has it that, by using pathway a, PPCS enzymes may select cysteine by using the difference in pi), values between thiols and alcohols and the higher nucleophilicity of thiolates to form the thioester 16 first, which subsequently rearranges to the thermodynamically more stable amide. Unfortunately, no experimental validation of this proposed mode of selection has been achieved as yet. 

The synthesis of the bis-cystinyl-octapeptide dimer in parallel alignment as present in the native human IgGl was achieved by the use of a selective cysteine-... 

Various organocatalyst-based hybrid catalysts were also prepared in this study [61]. For example, flavin 24 was used for the selective cysteine modification of the tHisF mutant Cys9Ala/AspllCys. This compound allows for direct quantification of chemical modification because it has chromophoric properties. In view of future en masse parallelized bioconjugation of mutant libraries in the process of directed evolution experiments (Fig. 3), the course of the chemical modification process was studied more... 

Other mPEG reagents bearing activated unsaturated bonds, such as mPEG acrylate, have also been used as Michael acceptor for selective cysteine PEGylation [197]. 

The sulfhydiyl group in cysteine can be selectively protected in the presence of the amino group by reaction with 2,4-dinitrophenol at pH 5-6. ... 

When cysteine reacts with an alkyl or aiyl chloroformate, both the —SH and —NH groups are protected as a thiocarbonate and as a carbamate, respectively. Selective or simultaneous removal of the protective groups is possible. 

InHBr, AcOH, 25°, 30min. The5-Cbzgroup is removed slowly under these conditions, but the N-Cbz group is completely cleaved, thus providing some selectivity in the protection scheme for cysteine. 

It is now apparent that bacteria have developed resistance to heavy metals and the detoxifying process is initiated and controlled by metallo-regulatory proteins which are able selectively to recognize metal ions. MerR is a small DNA-binding protein which displays a remarkable sensitivity to Hg +. The metal apparently binds to S atoms of cysteine and this has been a major incentive to recent work on Hg-S chemistry. 

British investigators (Haddow and Timmis 1951) synthesized and studied esters of the methanesulfonic acid. The most active derivative was the dimethylsulfonic ester of 1,4-butanedione, known as busulfan. Busulfan interacts with the thiol groups of proteins and amino acids some of its metabolites can alkylate the thiols of cysteine, peptides and proteins. Busulfan exerts selective cytotoxic activity in hematopoietic bone marrow cells and inhibits the formation of granulocytes and platelets. It slightly affects the lymphoid tissue. 

The Strecker reaction has been performed on the aldehyde 182 prepared from L-cysteine [86] (Scheme 28). The imine was formed in situ by treatment with benzylamine, then TMS cyanide was added to afford prevalently in almost quantitative yield the syn-diamine 183, which is the precursor of (-l-)-biotin 184. The syn selectivity was largely affected by the solvent, toluene being the solvent of choice. Since the aldehyde 182 is chemically and configurationally unstable, a preferred protocol for the synthesis of 183 involved the prehminary formation of the water-soluble bisulfite adduct 185 and the subsequent treatment with sodium cyanide. Although in this case the syn selectivity was lower, both diastereomers could be transformed to (-l-)-biotin. 

It is not only the activity that can be altered by incorporation of noncoded amino acids. Introduction of structures possessing certain chemical functions leads to the possibility of highly regioselective modification of enzymes. For example, selective enzymatic modification of cystein residues with compounds containing azide groups has led to the preparation of enzymes that could be selectively immobilized using click chemistry methods [99]. 

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