A semi‐quantitative investigation of the cysteic acid‐containing peptides in a partial acid hydrolysate of γ‐keratose

Abstract

Abstractγ‐Keratose, a soluble fraction of peracetic acid oxidised wool has been partially hydrolysed with 5 N hydrochloric acid under controlled conditions. The mixture of low molecular weight peptides has been separated into two fractions. The cysteic acid rich fraction contained 2750 μtmole/g of peptide‐bound cysteic acid. This accounts for 58% of the total cysteic acid present in γ‐keratose. The structures of a number of the cysteic acid peptides in this fraction have been deduced, and their amounts estimated on a semi‐quantitative basis. The following peptides have been identified and are listed in descending order of quantity present: Ser‐CySO3H.CySO3H.; Thr.CySO3H.CySO3H.; Gly.CySO3H.CySO3H.; CySO3H.;CySO3H.; CySO3H.Glu; Pro.CySO3H.CySO3H.; (Arg,CySO3H,CySO3H); Val‐(CySO3H)1–2. Without correction for losses during separation and analysis of the peptides it has been shown that at least 10.1% of the cysteic acid in γ‐keratose occurs in the sequence –CySO3H.CySO3H–. If a correction factor based on the recovery of cysteic acid from the analytical procedure is applied, then this sequence accounts for a minimum of 31.7% of the cysteic acid. Some consequences of a high incidence of this sequence are considered.