Keratins chemical modification

The easiest way to detect a protein modification seems to be the mass measurement of all peptides generated by enzymatic digestion. The comparison with the predicted peptide masses from the sequence of the protein identifies unmodified peptides and unexplained masses would give indications to modified peptides. Unfortunately, this is not a suitable approach in practice. In many peptide mapping experiments done with the MALDI mass mapping technique, up to 30% of the measured masses remain unexplained. This is probably due to protein contaminations from human keratins, chemical modifications introduced by gel electrophoresis and the digestion procedure, and other proteins present at low levels in the piece excised from the sodium dodecyl sulfate gel. The detection of a protein modification requires a more specific analysis. 

This section discusses two families of structural proteins, namely, extracellular keratins and collagens. Each example represents a family of closely related chemical entities, which means dealing with complex protein mixtures. We consider two types of chemical modifications modifications arising from increased levels of glucose in body fluids (obviously related to diabetes) and those derived from acetaldehyde, the first metabolic product of ethanol ingestion. As noted, a common feature of the latter nonenzymatic modification reactions is the presence of an aldehydic functionality in the nonprotein reactant (Jelfnkovd et al 1995 Deyl and Mikgik, 1995). 

This section is concerned primarily with the effects of chemical modifications of keratins on their physical properties—supercontraction, setting, swelling, load-extension characteristics, and other mechanical properties. Much of this work could be described by the term mechanochemical coined by Speakman (1947). The complexity of the cellular and sub-cellular structure of keratins necessitates the use of simplifying assumptions in the interpretation of mechanochemical experiments. 

The cystine residues, because they may act as cross-linkages between protein chains, have been studied more closely than other residues in keratin. Burley s (1956a) use of the concept of thiol-disulfide interchange to explain the effects of chemical modification on the physical properties of wool fibers has stimulated further work on cysteine and cystine residues. 

C. Effects of Chemical Modification on Physical Properties of Keratin Fibers... 

Watt, 1., Leeder, J., Effect of Chemical Modifications on Keratin and Water... 

In fact the absorption results are not greatly different there is a slight increase in the amount of water absorbed ( + 10% on average) and a simple shift of the energy profile (toward higher values in the case of reduced hair and toward lower values in the case of dyed hair). In total the chemical modifications involving the cystine do not lead to profound changes in the mechanism of water absorption at a molecular level for keratin. 

In conclusion, the large differences between natural collagen and keratin must be emphasized both in terms of the isotherm absorption and the nature of fixation sites of the water. We have shown that the influence of chemical modifications gives results which can be explained in terms of the model we have proposed. 

Martinez-Hernandez, A.L., Santiago-Valtierra A. L., Alvarez-Ponce M. J., (2008), Chemical modification of keratin biofibres by graft polymerisation of methyl methacrylate using redox initiation. Materials Research Innovations, Vol. 12, No. 4, (December 2008), pp 184-191, ISSN 1432-8917. 

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