Chemical modifications disulfide group

Although aggregation is the predominant means by which proteins become inactivated during refolding, several other inactivation pathways have also been observed. Proteins can be inactivated by thiol-disulfide exchange or alteration of the primary structure by chemical modification of amino acid side chains. In addition, refolded proteins may be inactivate due to the absence of prosthetic groups and metals or because of improper association of the subunits in multimeric proteins (79). 

The chemical modification by silani2a-tion (or other chemical reactions) of carbon, oxide, or metal electrode surfaces [21, 22] or SAM formation on gold surfaces with thiol or disulfide compounds [23] has been utilized for the tip functionalization. The systematic chemical derivatization of the tips was carried out with silane [10, 24-27] or thiol [17, 18, 20, 28-37] derivatives. Today, chemical differentiation of the terminal groups by FFM [5-20,28, 36, 37] or adhesive force measurements [17, 18, 20, 24-28, 30-37] is called chemical force microscopy (CFM) [17]. Adhesive and frictional forces can be mapped in x-y planes as CFM images. The adhesive... 

Expressed proteins are often modified by post-translational processing, which may include cleavages at specific residues chemical modifications to the amino or carboxy terminus or to specific residues formation of disulfide bonds or the addition of phosphate, sulfete, fatty acyl groups, or carbohydrate. Chemical modifications may occur as well during sample isolation and preparation. When the sequence of the protein is known or can be inferred from the gene sequence, the type and location of specific modifications can often be deduced from simple mass differences between the expected and observed peaks in an enzymatic map. Thus, Table 10.4 shows a list of common modifications, their sites, and the mass differences that would be observed. 

A final application of phase transfer catalysis to the chemical modification of I is the key step in the formation of a polymer bound thiothiazolone through reaction of I with carbon disulfide and glycine in basic medium with added tetrabutyl ammonium hydroxide. The open chain intermediate obtained in 90% functional yield can then be closed under mild conditions to afford the thiothiazolone which is currently being tested as a regenerable polymeric protecting group. 

Symptomatic solutions to counteracting mildew and insect infestation have employed various natural and synthetic insecticides that are selected for their specificity for the targeted species. Application methods for their maximum efficiencies must be specified. Some are noninvasive to humans and provide toxicity only to larvae while others are regulated compounds that could provide environmental risk. The broad range of development in this area includes chemical modification of wool s disulfide crosslinks and side-chain hydroxyl and amine groups. Applied topically or by infusion, certain aromatic or cyclic compounds are available under recognized trademarks. In recent years these approaches have been eclipsed by the use of pyrethroid insecticides such as permethrin. They can be used alone or coadded to conventional formulations. 

Most of the steps ofprotein folding involve chemical modification to help the protein to fold or to attach to metal ions, prosthetic groups, or other proteins to form the final, functional structure. The bonds can be covalent disulfide bonds formed by thiol oxidation, non-covalent hydrogen bonds, tu-tu stacks or electrostatic interactions. 

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