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Independent Determination of Cystine in Keratin Proteins

The role of cystine residues in a protein is well recognized, providing the disulfide bonds for the structural integrity of a wide range of proteins. Hence, the determination of cystine in proteins is critical in understanding the structural functionality of proteins. The amino acid analysis (AAA) is a popular method to determine amino acid residue compositions in proteins. In practice, oxidation of or chemical modification to cystine is often performed prior to AAA. However, these pretreatments are indiscriminate towards cystine and cysteine. Hence, it is difficult to distinguish cystine from cysteine in protein AA composition analyses, especially for cystine-rich proteins such as keratin. In this report, we demonstrate that it is possible to determine cystine residues in protein selectively independent from cysteine, using the conventional AAA, without pretreatments. Our experimental results have shown that cystine did not transform into cysteic acid during acid hydrolysis, as has been reported previously. Our results also showed a part of L-cystine transformed to D-cystine. Finally, we applied the same AAA to determine the cystine residue levels in feather and human hair samples successfully and compared those with the results obtained from AAA using the pretreatment by oxidation.

L-/D-cystine, D-cysteine, L-cysteine, Keratin, Amino Acid Analysis

APA Style

John M. Schulze, Ken Tasaki. (2022). Independent Determination of Cystine in Keratin Proteins. International Journal of Biochemistry, Biophysics & Molecular Biology, 7(2), 47-54. https://doi.org/10.11648/j.ijbbmb.20220702.11

ACS Style

John M. Schulze; Ken Tasaki. Independent Determination of Cystine in Keratin Proteins. Int. J. Biochem. Biophys. Mol. Biol. 2022, 7(2), 47-54. doi: 10.11648/j.ijbbmb.20220702.11

AMA Style

John M. Schulze, Ken Tasaki. Independent Determination of Cystine in Keratin Proteins. Int J Biochem Biophys Mol Biol. 2022;7(2):47-54. doi: 10.11648/j.ijbbmb.20220702.11

Copyright © 2022 Authors retain the copyright of this article.
This article is an open access article distributed under the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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