A new arylating agent, 2-carboxy-4,6-dinitrochlorobenzene: reaction with model compounds and bovine pancreatic ribonuclease

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. Nα-Acetylhistidine, Nα-acetyltyrosine and Nα-acetyltryptophan do not react. Poly (L-Lysine) and poly (DL-lysine) react about 50 times as fast as does Nα-acetyllysine. A dichloroanalog, 6-carboxy-2,4-dinitro-1,3-dichlorobenzene, shows stepwise reactivity with amines. With bovine pancreatic ribonuclease, which contains no sulfhydryl, CDNCB reacts preferentially with the e-amino of Lys-41 at 450 times the rate with the E-amino of Nα-acetyllysine. The preferential reactivity at Lys-41 is discussed in relation to the pK of Lys-41, the cationic character of the active site cleft, and the mechanism of RNAase action on substrates.