High-resolution electron microscopic study of the initial stage of collagen mineralization.

本研究旨在探讨胶原蛋白的初始矿化机制。标本是从含有不寻常胶原聚集物的牙本质样本中选择的。正常胶原蛋白的初始晶体（约2nm厚）呈针状或薄血小板状。根据晶体形态，最初的晶体被认为是由氢磷灰石或磷酸八钙组成的。但是，由于无法清楚地看到晶体晶格和微区电子衍射图，我无法确定晶体类型。成熟晶体（约4nm厚）呈血小板状。它们的晶格间距（约0.82nm）为氢化磷灰石。不同寻常的胶原蛋白聚集体上的晶体也产生了类似的结果。由于不寻常的胶原蛋白聚集体既不形成周期性条纹，也不形成孔洞带，因此它们的矿化与这两种现象无关。由于晶体的c轴方向与胶原蛋白分子的长轴方向一致，晶体似乎开始沿着胶原蛋白分子纵向沉积。综上所述，本研究表明胶原蛋白的初始矿化包括三个过程：1)胶原分子间磷酸八钙的初始沉淀，2)磷酸八钙随后转化为羟基磷灰石，3)羟基磷灰石的晶体生长。

The purpose of this study is to investigate the initial mineralization mechanism of collagen.Specimens were selected from examples of dentin containing unusual collagen agregates. Initial crystals (about 2nm thick) on normal collagen assumed needle or thin-platelet shape. On the basis of crystal morphology, initial crystals were thought to be made up of hydroxiapatite or octacalcium phosphate.But, since it was impossible to view crystal lattices and micro-area electron diffraction patterns clearly, I was unable to determine crystal type.Mature crystals (about 4nm thick) were platelet-like in shape.Their crystal-lattice spacing (about 0.82nm) indicated hydroxiapatite.Similar results were produced from crystals on unusual collagen agregates.Because unusual collagen agregates form neither periodic striations nor hole zone, their mineralization occurs independent of both these phenomena.Since the direction of the crystal c-axis coincides with that collagen-molecule long axis, it seems that crystal commence depositing lengthwise along collagen molecules.In conclusion, this study suggests that the initial mineralization of collagen comprises three events : 1) initial precipitation of octacalcium phosphate between collagen molecules, 2) subsequent transformation of octacalcium phosphate into hydroxiapatite, and 3) crystal growth of this hydroxiapatite.