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Tyrosinase-catalyzed grafting of sericin peptides onto chitosan and production of protein–polysaccharide bioconjugates

Paper ID Volume ID Publish Year Pages File Format Full-Text
25491 43576 2007 12 PDF Available
Title
Tyrosinase-catalyzed grafting of sericin peptides onto chitosan and production of protein–polysaccharide bioconjugates
Abstract

The capability of Agaricus bisporus tyrosinase to catalyze the oxidation of tyrosine residues of silk sericin was studied under homogeneous reaction conditions, by using sericin peptides purified from industrial wastewater as the substrate. Tyrosinase was able to oxidize about 57% of sericin-bound tyrosine residues. The reaction rate was higher than with silk fibroin, but lower than with other silk-derived model peptides, i.e. tryptic and chymotryptic soluble peptide fractions of silk fibroin, suggesting that the size and the molecular conformation of the substrate influenced the kinetics of the reaction. The concentration of tyrosine in oxidized sericin samples decreased gradually with increasing the enzyme-to-substrate ratio. The average molecular weight of sericin peptides significantly increased by oxidation, indicating that cross-linking occurred via self-condensation of o-quinones and/or coupling with the free amine groups of lysine and, probably, with sulfhydryl groups of cysteine. The high temperature shift of the main thermal transitions observed in the differential scanning calorimetry curves confirmed the formation of peptide species with higher molecular weight and higher thermal stability. Fourier transform-infrared spectra of oxidized sericin samples showed slight changes related to the loss of tyrosine and formation of oxidation products. Oxidized sericin peptides were able to undergo non-enzymatic coupling with chitosan. Infrared spectra provided clear evidence of the formation of sericin–chitosan bioconjugates under homogeneous reaction conditions. Spectral changes in the NH stretching region seem to support the formation of bioconjugates via the Michael addition mechanism.

Keywords
Silk sericin; Chitosan; Tyrosinase; HP-SEC; FT-IR; DSC
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Tyrosinase-catalyzed grafting of sericin peptides onto chitosan and production of protein–polysaccharide bioconjugates
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Biotechnology - Volume 127, Issue 3, 10 January 2007, Pages 508–519
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us