A NEW ARYLATING AGENT, 2-CARBOXY-4,6-DINITROCHLOROBENZENE Reaction with Model Compounds and Bovine Pancreatic Ribonuclease

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Abstract
The reagent 2-carboxy-4,6-dinitrochlorobenzene (CDNCB) reacts with the imino, amino and sulfhydryl groups of model compounds. At pH 8.2, sulfhydryl groups react much faster than do amines. N.alpha.-Acetylhistidine, N.alpha.-acetyltyrosine and N.alpha.-acetyltryptophan do not react. Poly(L-Lysine) and poly(DL-lysine) react about 50 times as fast as does N.alpha.-acetyllysine. A dichloroanalog, 6-carboxy-2,4-dinitro-1,3-dichlorobenzene, shows stepwise reactivity with amines. With bovine pancreatic RNase, which contains no sulfhydryl, CDNCB reacts preferentially with the .epsilon.-amino of Lys-41 at 450 times the rate with the .epsilon.-amino of N.alpha.-acetyllysine. The preferential reactivity of Lys-41 is discussed in relation to the pK of Lys-41, the cationic character of the active site cleft and the mechanism of RNase action on substrates.