Photolysis of desmosine and isodesmosine by ultraviolet light.

It is known that the pyridinium ring of a model compound such as N-methyl pyridinium chloride is cleaved by U.V. radiation at 254 nm. At acid pH the products obtained are methylamine and glutaconaldehyde. Under the same conditions desmosine and isodesmosine are degraded into lysine and probably into the homologous substituted ketone of glutaconaldehyde. At pH 6.0-7.0, a transient open-chain aminoaldehyde intermediate is observed which can either reform the original compound or be cleaved as at low pH. When intact elastin is photolysed for 20 minutes in water, approximately 75% of the (iso) desmosines are destroyed, accompanied by an increase of free lysine residues. No change in the concentration of the other amino acids, including tyrosine, are noted. It is therefore likely that the crosslinks engaged in peptide links are also cleaved photochemically.