Structure of elastic-fiber microfibrils more dynamic than that in non- elastic tissue

Elastic fibers are composed of peripheral microfibrils and a core of elastin. Whether elastic-fiber microfibrils are specialized and whether their structure differs from that in non-elastic tissues remain to be determined, however. In this study, the ultrastructure of elastic-fiber microfibrils was examined in monkey (Macaca mulatta and Macaca fuscata) gingiva. In contrast to the straight microfibrils observed in non-elastic tissues, they were bent and irregular, and the outermost layer was an aggregate of 3-nm wide, ribbon-like structures previously identified as chondroitin sulfate proteoglycan (CSPG) double-tracks. In contrast, it was reported that the surface layer of non-elastic tissue microfibrils was made up of 4.5-nm wide, heparan sulfate proteoglycan (HSPG) double-tracks. The binding of glucuronic acid-rich chondroitin sulfate to other substances is weaker than that of iduronic acid-rich heparan sulfate. This suggests that CSPGcontaining elastic-fiber microfibrils are less solid and have a more dynamic structure (softer microfibrils) than HSPGcontaining, more solid non-elastic tissue microfibrils. This would allow conformation to be altered more easily, which might be expected where elasticity were required.