Partially Carboxymethylated Feather Keratins. 1. Properties in Aqueous Systems

Abstract

Feather keratins were extracted from chicken feathers with an aqueous solution of urea and 2-mercaptoethanol. The keratin solution obtained was dialyzed to remove the reagents. Upon dialysis, extensive protein aggregation occurred. To obtain stable solutions or dispersions in water, cysteine residues were modified prior to dialysis with iodoacetamide, iodoacetic acid, or bromosuccinic acid, thereby blocking free thiol groups and introducing hydrophilic groups. For the development of biodegradable materials with good mechanical properties from these biopolymers, disulfide bonds between the keratin molecules are needed. Therefore, cysteine residues were only partially modified by using different reagent/cysteine molar ratios. The reaction rate constants of iodoacetate with glutathione and 2-mercaptoethanol were successfully used to predict the degree of modification of keratin cysteine. It was shown that, for carboxymethylated keratin, fewer aggregates were formed for higher degrees of cysteine modification, while more protein was present as oligomers. Aggregates and oligomers were stabilized through intermolecular disulfide bonds.

Alternative Methods of Preparation of Soluble Keratin from Chicken Feathers

“…Although the yield was also high when DTT was used, the solution obtained by this method became partially insoluble after dialysis, so this reducing agent was not suitable. Schrooyen et al [16] reported the yield of keratin extracted from feathers by 2-mercaptoethanol to be approximately 75 %. Poole et al [32] showed that sodium sulphite gave a yield of 62 %.…”

“…Reduction of keratin by 2-mercaptoethanol, dithiothreitol (DTT) or dithioerythritol, thioglycolic acid, glutathione, sulphites, and bisulphite generates free cysteine residues, and the resulting cysteine-containing derivatives are called ''kerateines'' [7,[15][16][17][18]. They are less polar and more stable in acidic and alkaline solutions than the oxidized derivatives, and they contain amino acid residues capable of re-crosslinking.…”

“…As the majority of the keratin remains trapped within the protective structures, during this reaction a denaturing solvent, such as urea, thiourea, transition metal hydroxides, surfactant solutions, and combination thereof should be applied, to limit the effects of ionic and hydrogen bonds interaction [16,20]. In turn, addition of sodium dodecylsulfate (SDS) provides faster and more efficient extraction by formation of complexes keratin-SDS, and prevents protein aggregation [15].…”

Changes in Human Hair Induced by UV- and Gamma Irradiation

“…The increasing amount of free sulfhydryl groups (-SH-) in keratin can originate from disruption of the disulfide cysteine bonds (-SS-) induced by radiation. The breaking of all of these disulfide bonds in cysteine, may results in the amount of cysteine equals 720 μmol/g of feathers [13]. Data presented in Figure 5 show that after exposure to 10Gy gamma radiation a sulfohydril group content in hair keratin change insignificantly from 0.21 μmol/g in non-radiated hair to 0.29 μmol/g in irradiated hair, which indicates that only less than 10% of the disulfide bonds were broken.…”

<b>Direct Observation of Hair Components Involved in Formation of Permanent Waves</b>

“…The content of free and disulphide bond-forming thiol-containing residues in hydrolyzed keratin was measured by using 2-nitro-5-thiosulphobenzoate and 5,5-diothiobis(2-nitrobenzoic acid) (Ellman's reagent) according to the method of Shrooyen et al [23]. Absorbance measurement was carried out at 412 nm using a TECAN Infinite M200 micro plate reader (Kanagawa, Japan).…”