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Original Article

Selective Free Radical Reactions with Proteins and Enzymes: The Inactivation of α-chymotrypsin

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Pages 39-46 | Received 08 Feb 1974, Accepted 09 Apr 1974, Published online: 03 Jul 2009
 

Summary

The reactions of the selective free radicals (CNS)2 and Br2 with α-chymotrypsin have been studied by pulse radiolysis and steady-state inactivation measurements.

Rate-constants for the reaction have been measured over the pH range 7 to 12. The reactivity increases at pH 11 where the tyrosine residues deprotonate. Transient product spectra also indicate a significant increase in attack at tyrosine at this pH. A small increase in rate was observed by lowering the salt concentration from 10−1 M to 4 × 10−2 M.

The inactivation data show (CNS)2 to be protective relative to OH over the pH range 2 to 11, whereas Br2 sensitizes between the pH range 4 and 9.

From the pulse radiolysis and inactivation data, it was concluded that a histidine residue was essential to the activity of α-chymotrypsin.

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