Purification
of elastin can be accomplished by hydrolytic procedures using acids or alkali, enzymes, or autoclaving (l-3). The resulting preparations can be standardized and characterized only by their amino acid composition
(1,4,5) and mainly by their desmosine and isodesmosine contents (6-9). These cross-linking amino acids are the only specific earmarks of elastin. Some other cross-linking amino acids are also present, as lysinonorleucine (10) and an intermediary product of desmosine which can be converted to merodesmosine (11). However the former is present in collagen also (12,13), and is probably identical with the aldol condensation product of two allysines, yielding on reduction a derivative which was isolated and characterized ( 14).
These considerations render important the specific determination of these cross-linking amino acids of elastin. The methods proposed for desmosine determination all use the amino acid analyzer (6-9). We propose here a simpler and faster procedure which enabled us to carry out serial determinations of cross-linking amino acids in several elastin preparations purified by different methods (3). This procedure is based on the separation of the cross-linking amino acids from the neutral, acid, and basic amino acids by high-voltage electrophoresis. The ninhydrincoloured strips are then quantitated by densitometric recording. The same method can be used for the isolation of small quantities of cross-linking amino acids by preparative electrophoresis followed by elution of the spots from the paper. This method enabled us to carry out the characterization of some of the isolated substances by thin-layer chromatography and by mass spectrometry (15).
Methods
The preparation and purification of elastin samples were carried out as described earlier (3,15).