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.