Elastin was prepared from calf ligamentum nuchae with several methods using the following solvents for the extraction of extraneous (non-elastin) proteins : 0.1 N NaOH a t 100 "C, 88 formic acid a t 45 "C, 7001, trichloracetic acid at + 4 "C, 5 M guanidine HCl with a thiol reagent and autoclaving in water. All elastin samples contained small amounts of carbohydrate. Electron microscopy showed the presence in all samples of electron-translucent lamellae and osmiophilic uranyl-lead stainable "microfibrillar" eIements.The osmiophilic "microfibrils" decreased strongly in the elastin preparations after extractionThese solvents extracted a significant proportion of the hexose content of the elastin samples with only 6--7O/, o f their protein content. Similar results were obtained with chymotrypsin digestion although this enzyme acts less selectively than the above mentioned solvents and degrades elastin also.When 1Z5I-labelled elastin was used for extraction with 8 M urea-0.1 M mercaptoethanol the extracted glycopeptides had a significantly higher specific activity than the residual elastin. These results suggest that the microfibrillar elements are derived from or are identical with the structural glycoproteins which were extracted from elastin-rich tissues by identical proceduresThe presence of glycoprotein in varying proportions in purified elastin preparations can explain the variation of its amino acid content (ratio of polar to non-polar amino acids) with age or in certain pathological conditions (atheromatosis, emphysema) and some of its immsnochemical properties (cross reactions with structural glycoproteins). r121.Electron microscopic stiidies performed by several investigators on elastic fibers showed the presence of essentially two distinct types of structural elements : a homogenous, electron-transparent material, and a "microfibrillar" component, stainable with uranyl acetate and lead [I-51. Our recent studies indicated a chemical and immunological heterogeneity of purified elastin preparations [ 17,181 ; the structural glycoprotein fractions of aorta gave cross reactions with kappaelastin prepared from purified aorta elastin [18]. These results suggested the presence of common antigenic determinants in structural glycoprotein and elastin preparations. Therefore it appeared essential to

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