Quantitation of the epsilon-(gamma-glutamyl)lysine cross-link using a high-speed amino acid analyzer without purification of the dipeptide. Application to enzymatic digested mixtures of keratin and the membranous fraction of human stratum corneum.

epsilon-(gamma-Glutamyl)lysine in an enzymically digested mixture of keratin and the membranous fraction of human stratum corneum was directly quantitated using a high-speed amino acid analyzer without purification of the dipeptide. The analytical conditions were improved so that epsilon-(gamma-glutamyl)lysine clearly separated from other amino acids and eluted directly after tyrosine. The enzymatically digested mixtures were filtered through an Ultra Free membrane and deammoniated before analysis. By our present method, keratin and the membranous fraction of human stratum corneum were analyzed and 5.8 and 43.5 nmol/mg of epsilon-(gamma-glutamyl)lysine, respectively, were detected.