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Chemical Modification of Xylanase from Trichosporon cutaneum Shows the Presence of Carboxyl Groups and Cysteine Residues Essential for Enzyme Activity

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Abstract

The endo-β-1,4-xylanase (EC 3.2.1.8) from Trichosporon cutaneum was chemically modified using amino acid-specific reagents. The enzyme does not bear arginines essential for activity, since 1,2-cyclohexanedione and 2,3-butanedione, although they modify the enzyme (after chromatographic analysis), have no effect on its activity. Reaction of the enzyme with tetranitromethane and N-acetylimidazole did not result in a significant activity loss as a result of modification of tyrosine residues. The water-soluble carbodiimide 1-[3-(dimethylamino) propyl]-3-ethylcarbodiimide inactivated the xylanase rapidly and completely in a pseudo-first-order process, and kinetic analysis indicated that at least one molecule of carbodiimide binds to the enzyme for inactivation. A mixture of neutral xylooligomers provided significant protection of the enzyme against this carbodiimide inactivation. Reaction of the xylanase with 2,4,6-trinitrobenzene sulfonic acid did not result in a significant activity loss as a result of modification of lysine residues. Titration of the enzyme with 5,5′-dithiobis-(2-nitrobenzoic acid) and treatment with iodoacetamide and p-chloromercuribenzoate indicated the presence of a free/active thiol group. Xylan completely protected the enzyme from inactivation by p-hydroxymercuribenzoate, suggesting the presence of cysteine at the substrate-binding site. Inactivation of xylanase by p-hydroxymercuribenzoate could be restored by cysteine.

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Wen, L., Miao, Z.W. & Qing, W.D. Chemical Modification of Xylanase from Trichosporon cutaneum Shows the Presence of Carboxyl Groups and Cysteine Residues Essential for Enzyme Activity. J Protein Chem 18, 677–686 (1999). https://doi.org/10.1023/A:1020658307787

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  • DOI: https://doi.org/10.1023/A:1020658307787

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