Abstract
A new reagent, monochlorotrifluoro-p-benzoquinone (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 [EC 2. 7. 7. 16], chymotrypsinogen, α-chymotrypsin [EC 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 B1 Phe in the insulin molecule is the single amino group reactive with CFQ, and the α-amino group of A1 Gly and the α-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 B1 Phe reactive both with CFQ and with NQS, the α-amino group of A1 Gly reactive with NQS but not reactive with CFQ and the ε-amino group of B29 Lys not reactive with these reagents. A possibility of intra-chain hydrogen bonding of the amino group of A1 Gly with the carboxyl group of A4 Glu was discussed.
