States of Amino Acid Residues in Proteins XIII. Monochlorotrifluoroquinone as a New Reagent for Discrimination of Amino Groups

A new reagent, monochlorotrifluoro-pbenzoquinone (abbreviated to CFQ) was explored as a means for discriminating amino groups in proteins, and the following facts were revealed, applying the reagent to proteins. The reagent possesses a moderate reactivity suitable for the discrimination; 1, 1, 3, 7, 8, 10 and 8 out of the total 2, 3, 7, 11, 15, 17 and 17 amino groups in the molecules of glucagon, insulin, lysozyme [EC 3.2.1.17], pancreatic ribonuclease [EG 2.7.7.16], chymotrypsinogen, a-chymotrypsin [EG 3.4.4.5] and diisopropylphosphoryl(DIP)-chymo-trypsin, respectively, are reactive with this reagent. The reactivity of CFQ is, therefore, lower than that of β-naphthoquinone-4-sulfonic acid (NQS). The terminal α-amino group of B 1 Phe in the insulin molecule is the single amino group reactive with CFQ, and the a-amino group of Al Gly and the amino group of B29 Lys are the non-reactive type. In terms of the reactivities with CFQ and with NQS, the amino groups of insulin can be classified into three types; the α-amino group of Bl Phe reactive both with CFQ and with NQS, the α-amino group of Al Gly reactive with NQS but not reactive with GFQ and the α-amino group of B29 Lys not reactive with these reagents. A possibility of intra-chain hydrogen bonding of the amino group of Al Gly with the carboxyl group of A4 Glu was discussed.