Guanidination of the Lysine Residues Present in Fibrous Elastin and in Soluble Elastin Peptides

Abstract

We have found that only 20 to 30% of the lysine residues measured after acid hydrolysis of insoluble elastin and α-elastin were blocked by prior guanidination of elastin with o-methylisourea. In contrast free lysine was guanidinated almost 100% and a purified, highly crosslinked peptide fraction of low molecular weight, 85%. The non-reactivity of lysine does not seem to be due to steric hindrance in the fibrous protein or in the large peptides derived therefrom but rather to the presence of ϵ[δ-adipic acid]-lysine. the oxidized form of lysinonorleucine described by Bailey et al.⁴

Since photolysis of desmosine and isodesmosine leads also to the formation of new lysine residues, methods will have to be devised to distinguish lysine-containing peptides derived from photolyzed elastin.