Interchain covalent bonds

It is known that proteins can be chemically modified in the presence of free radicals with formation of cross-links [13], The goals of the work were to create stable protein coating on the surface of individual MNPs using a fundamentally novel approach based on the ability of proteins to form interchain covalent bonds under the action of free radicals and estimate activity of proteins in the coating. 

Size Isomers. In solution, hGH is a mixture of monomer, dimer, and higher molecular weight oligomers. Furthermore, there are aggregated forms of hGH found in both the pituitary and in the circulation (16,17). The dimeric forms of hGH have been the most carefully studied and there appear to be at least three distinct types of dimer a disulfide dimer connected through interchain disulfide bonds (8) a covalent or irreversible dimer that is detected on sodium dodecylsulfate- (SDS-)polyacrylamide gels (see Electroseparations, Electrophoresis) and is not a disulfide dimer (19,20) and a noncovalent dimer which is easily dissociated into monomeric hGH by treatment with agents that dismpt hydrophobic interactions in proteins (21). In addition, hGH forms a dimeric complex with ( 2). Scatchard analysis has revealed that two ions associate per hGH dimer in a cooperative... 

Similarly, polymers dissolve when a solvent penetrates the mass and replaces the interchain secondary bonds with chain-solvent secondary bonds, separating the individual chains. This cannot happen when the chains are held together by primary covalent cross-links. Thus, linear and branched polymers dissolve in appropriate solvents, whereas cross-linked polymers are insoluble, although they may be swelled considerably by absorbed solvent. 

Collagen triple helices are stabilized by hydrogen bonds between residues in dijferent polypeptide chains. The hydroxyl groups of hydroxyprolyl residues also participate in interchain hydrogen bonding. Additional stability is provided by covalent cross-links formed between modified lysyl residues both within and between polypeptide chains. 

Insulin is the protein that has been most investigated for pulmonary administration. Insulin levels are not maintained in diabetic patients, and precise control over blood glucose levels is needed. Insulin is a small protein, 5.8 kDa, which is composed of two chains that are covalently linked by an interchain disulfide bond. Currently, insulin is administered by injection, several times a day for many diabetics. The ability to deliver insulin via a noninvasive route would free diabetics from inconvenient, invasive insulin delivery methods and possibly eliminate secondary problems associated with diabetes, such as diabetic retinopathy. 

Although both IFN-7 and lL-10 swap the same secondary structural elements (helices E and F) to form the dimers, their quaternary structures are very different. IFN-7 and lL-10 adopt inter-domain angles of approximately 60° and 90°, respectively. More recently, the structure of cmvIL-10 revealed a domain angle of approximately 150° (Jones et al, 2002b). In addition, the two cmvIL-10 peptide chains form an interchain disulfide bond while IFN-7 and cellular IL-10 are non-covalent dimers. The domain orientations of each dimer are essentially fixed at one unique inter domain angle which alters the orientation of the cell surface receptors and may ultimately modulate cellular signal transduction events. 

From the heat capacities of EiPis and KP15, it was derived that the soft vibrational modes at low temperatme are only affected by interaction between the metal cation and the six nearest neighbors. Therefore, the covalently bonded Pi5 tubes and the ionic interaction between the cation and the polyanion produce two distinctly separate sets of vibrational excitations (see below). At low temperatures, interchain vibrations occur, partially transmitted through the cations. At higher temperatures, intrachain vibrations, propagated through the covalently bonded tubes, are the dominant vibrational modes. 

The structure must somehow accommodate the various unusual covalent bonds (e.g., hydroxylamine-sensitive ester-type bonds, 7-car-boxylglutamyl and e-aminolysyl peptide linkages, see Section V) which have been reported in collagen and gelatin and which may possibly be involved in interchain cross-linking. 

---