Selective free radical reactions with proteins and enzymes. The inactivation of subtilisin Carlsberg and subtilisin Novo

Abstract
Reactions of the selective inorganic radical anions (SCN) 2 and Br 2, with subtilisins Novo and Carlsberg lead to selective oxidation of the tryptophan, tyrosine, and histidine amino-acid residues. Inactivation studies show that most of the inactivation is caused by oxidation of one or more histidine residues. Oxidation of tryptophan residues has a minor effect upon activity but damage to tyrosine residues does not affect the activity of the two enzymes towards the small synthetic substrate N-acetyl-L-tyrosine ethyl ester. Rate constants for reactions with the radical anions and transient spectra, measured by pulse radiolysis, reflect the differences in amino-acid composition and in structure between the two enzymes.

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