The Isolation of Chemically Pure Elastins in a Form Suitable for Mechanical Testing

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Abstract
Highly purified elastic fibers have been prepared by three different techniques from adult bovine ligamentum nuchae in the form of strips suitable for scanning electron microscopy7 and for mechanical testing. The purity of these ehstins has been controlled by amino acid analyses carried out on samples withdrawn at given time intervals during enzymatic, alkaline and formic acid pretreatments. Mechanical testing of intact ligamentum nuchae revealed two distinct phases during extension; the first phase was a reflection of the extension of elastin fibers while the second phase was a reflection of the extension of collagen fibers. The first phase could be studied independently by using strips of elastin fibers prepared by enzymatic or alkaline pretreatment which removed all the collagen. Although the formic acid treatment also removed the collagen, partial destruction of the desmosine and isodesmosine cross-links and also peptide bonds took place with the resultant loss in stiffness of the elastin fibers compared to the control, enzyme and alkaline processed elastins. N-Terminal analysis on the enzymatic and alkaline-pretreated elastin fibers established that no marked cleavage of peptide bonds took place within the elastin fibers during these pretreatments; these fibers had an average chain weight of 3.0–3.2 × 105. On the other hand, the prolonged digestion with formic acid reduced the average chain weight to 0.8 × 105. It was concluded that the enzymatic pretreatment yielded elastin fibers which were most typical of native elastin fibers.