Two forms of apatite deposited during mineralization of the hen tendon

Electron holography of biological samples

“…The specific properties of collagen in biomineralisation phenomena are determined not only by its structure but also by different modifications and interactions with non-collagenous proteins, proteoglycans, glycosaminoglycans and possibly mono-or oligomeric sugars initiating or directing mineralisation (Ehrlich et al, 2005b;He and George, 2004). In spite of that electron microscopical image processing approach of collagen mineralisation was recently reported (Tzaphlidou, 2005;Giraud Gille et al, 2005;Ono and Nemoto, 2005;Asawa et al, 2004), yet it is still not clear at which sites in the collagen fibre mineralisation by hydroxyapatite occurs. Divergent models (Prostak and Lees, 1996) have been proposed to explain mineralisation of collagen-containing tissue structures: in one model, intrafibrillar crystallites are oriented parallel to each other and to the longitudinal collagen fibril axis; a second model proposed that the intrafibrillar crystallites alternated their orientation with respect to each other both within individual gap zones and subsequent gap zones along the whole length of the fibril; a third model postulated that crystallite growth actually changes the structure of the collagen fibril; in a fourth model, intrafibrillar crystallites of bone were oriented at an acute angle to the long axis of the collagen fibril, and the extrafibrillar crystallites surrounded the intrafibrillar crystallites.…”