Lu H K, Huang C M, Li C W
Institute of Life Science, National Tsing Hua University, Hsinchu, Taiwan, Republic of China.
Exp Cell Res. 1995 Jul;219(1):137-45. doi: 10.1006/excr.1995.1214.
The radula of the limpet, Cellana toreuma, consists of a continuous series of teeth in various stages of iron biomineralization. The major iron-binding protein of the limpet's iron-containing granule (siderosome) has been purified and identified as ferritin. Limpet ferritin has a M(r) of 575 kDa and can be resolved into two bands by SDS-PAGE analysis, with respective M(r)s of 26 and 21 kDa. The partial N-terminal amino acid sequences of these two subunits were confirmed, and antisera against them were respectively generated. The specifity of these two antisera shows no difference between them. By using transmission electron microscopy and immunogold staining techniques the following two events were revealed: (1) in the superior epithelial cell of the radula, ferritin was disassembled through autophagy or heterophagy before exocytosis; (2) of the limpet ferritin, at least the 26-kDa subunit was found to pass through the microvilli, resulting in the accumulation of iron in the extracellular tooth chamber and the formation of goethite needles. Intracellular ferritin being translocated to the extracellular environment is discussed in the text.
笠贝（Cellana toreuma）的齿舌由一系列处于不同铁生物矿化阶段的连续齿组成。笠贝含铁颗粒（铁体）的主要铁结合蛋白已被纯化并鉴定为铁蛋白。笠贝铁蛋白的分子量为575 kDa，通过SDS-PAGE分析可分为两条带，各自的分子量为26 kDa和21 kDa。确认了这两个亚基的部分N端氨基酸序列，并分别制备了针对它们的抗血清。这两种抗血清的特异性没有差异。通过透射电子显微镜和免疫金染色技术揭示了以下两个事件：（1）在齿舌的上皮细胞中，铁蛋白在胞吐作用之前通过自噬或异噬作用被分解；（2）发现笠贝铁蛋白中至少26 kDa的亚基穿过微绒毛，导致铁在细胞外齿腔中积累并形成针铁矿针。文中讨论了细胞内铁蛋白向细胞外环境的转运。
