The reaction of iodobenzene-p-sulphonyl chloride (pipsyl chloride) with certain amino acids and peptides, and with insulin

1. A system of separation using buffered Celite columns is described that enables the pipsyl derivatives of most of the common amino acids to be separated. 2. The reaction of pipsyl chloride with several amino acids not included in previous studies has been investigated. In particular, knowledge of the acid-soluble pipsyl derivatives of arginine, histidine, lysine, tyrosine and cysteic acid has been extended. 3. Reproducible factors have been obtained that enable corrections to be applied for the breakdown of pipsylamino acids on acid hydrolysis. 4. The reaction of pipsyl chloride with peptides has been studied under various conditions. 5. The extent of the reaction between pipsyl chloride and insulin depends on the nature of the solvent–buffer system, and under the best conditions so far found is about 75% complete. 6. In an Appendix, the separation of pipsylamino acids by thin-layer chromatography is described.     

The reaction of tryptophan with cystine during acid hydrolysis of proteins. Formation of tryptathionine as a transient intermediate in a model system

Under the conditions commonly used to hydrolyze proteins with 6 M HCl, tryptophan reacted with cystine to give a transient intermediate, which was isolated and identified as 2-(2-amino-2-carboxyethylthio)tryptophan (tryptathionine) by NMR studies, etc. Studies on the formation and degradation of the above compound showed that beta-3-oxoindolylalanine and cysteine, which were previously reported to be the main degradation products of tryptophan and cystine, respectively, are formed by the hydrolysis of this intermediate during the course of the reaction.