Isolation of a New Type of Cross Link from the Hinge Ligament Protein of Molluscs

Abstract

THE two best known elastic proteins are elastin and resilin. So far, elastin has been, isolated only from vertebrates although the presence of elastin-like material has been reported in several invertebrates^1,2. Resilin has been found only in arthropods³. Apart from their amino-acid composition, resilin and elastin differ in the way they are cross linked into three dimensional networks. Thus resilin contains di- and tri-tyrosine formed oxidatively from tyrosine residues^4,5 and elastin contains desmosine and isodesmosine⁶ together with a small amount of lysinonorleucine⁷, all formed from lysine residues. The presence in foetal elastin of dityrosine has recently been reported⁸. During an investigation of elastic proteins from other phyla, I noticed that molluscan hinge ligaments contain phenolic compounds, which in several respects resemble dityrosine (Fig. 1). One of these compounds (compound A) has now been isolated and identified as 3,3′-methylene-bistyrosine (Fig. 2). The isolation procedure and the reasons for ascribing the structure in Fig. 2 to the compound are described in this communication; a more detailed description of the properties of the compound will be published later.