Reaction of 2-hydroxy-5-nitrobenzylated carboxypeptidase a with 14C-1-Fluoro-2,4-dinitrobenzene

Abstract

Summary Carboxypeptidase A was treated with dimethyl(2-hydroxy-5-nitrobenzyl)-sulfonium chloride, in 20 times its molar concentration, at pH 7.5. Hydroxy-nitrobenzylated enzyme was isolated from the reaction mixture and examined for modification of amino acid residues. Modification of tryptophan was evidenced both by diminished recoveries from a variety of acid hydrolysates, and from quenching of indole fluorescence of the modified protein in denaturing as well as non-denaturing solvents. N-Terminal amino group alkylation did not appear to have occurred, on the basis of essentially full recoveries of α -N-DNP-amino acids from acid hydrolysates following reaction of the enzyme with 14 C-fluorodinitrobenzene.