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首页> 外文期刊>Protoplasma: An International Journal of Cell Biology >POLYANION-MEDIATED MINERALIZATION - A KINETIC ANALYSIS OF THE CALCIUM-CARRIER HYPOTHESIS IN THE PHYTOFLAGELLATE PLEUROCHRYSIS CARTERAE
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POLYANION-MEDIATED MINERALIZATION - A KINETIC ANALYSIS OF THE CALCIUM-CARRIER HYPOTHESIS IN THE PHYTOFLAGELLATE PLEUROCHRYSIS CARTERAE

机译：离子介导的矿化作用-运动性小AGE肉毛囊菌中钙载体假说的运动学分析

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Polyanions are postulated intermediates in biomineralization because they sequester large numbers of calcium ions and occur in high concentrations at mineralizing foci in distantly related organisms. In this study mineral ion and polyanion metabolism was examined in Pleurochrysis carterae to determine whether polyanions function as intermediate calcium-carriers during coccolith (mineralized scale) formation. In this organism mineralization occurs intracellularly in coccolith-forming saccules, and mature coccoliths are extruded through the plasma membrane into the coccosphere. The polyanions (acidic polysaccharides known as PS-1 and PS-2) are synthesized in medial Golgi cisternae and transported to the coccolith-forming saccule prior to the onset of mineral deposition; they also cover the mineral surface of mature coccoliths. Pulse-chase experiments with Ca-45(2+) and (CO32-)-C-14 show the calcium uptake into the coccolith-forming saccule is much slower than carbonate uptake. The extended intracellular half-life of calcium ions destined for the coccosphere suggests that calcium is initially sequestered in more distal Golgi elements (perhaps in association with the polyanions) and enters the coccolith-forming saccule only after passage through the endomembrane system. This is consistent with previous cytochemical studies showing that the polyanions are complexed with calcium prior to mineral deposition. It has been suggested that polyanions may be degraded at the mineralization front in order to free calcium ions for precipitation with available carbonate or phosphate ions. However, this study demonstrates that the polyanions are not degraded; essentially all PS-1 and PS-2 are eventually secreted with the mineral phase into the coccosphere. The kinetics of mineral ion and polyanion secretion are consistent with a polyanion-mediated calcium transport; however, the manner in which calcium might be sequestered by and freed from the polyanions is still obscure. [References: 15]
机译：聚阴离子是生物矿化中的假定中间体，因为它们会螯合大量钙离子，并在远缘相关生物的矿化灶中以高浓度存在。在这项研究中，检查了软骨菌中的矿物质离子和聚阴离子代谢，以确定聚阴离子是否在椰油石（矿化鳞片）形成过程中充当中间钙载体的作用。在这种生物中，矿化作用发生在形成球囊的囊泡的细胞内，成熟的球囊通过质膜被挤出到球囊中。聚阴离子（称为PS-1和PS-2的酸性多糖）是在高尔基池的内侧合成的，并在矿物沉积开始之前转运到形成球藻的囊泡中。它们还覆盖了成熟球石的矿物表面。用Ca-45（2+）和（CO32-）-C-14进行的脉冲追踪实验表明，钙对形成球囊的球囊的钙吸收比碳酸盐的吸收要慢得多。进入球囊的钙离子的延长的细胞内半衰期表明，钙最初被螯合在更多的远端高尔基体中（也许与聚阴离子结合），并且仅在通过内膜系统后进入形成球囊的囊泡。这与以前的细胞化学研究一致，后者表明聚阴离子在矿物质沉积之前先与钙络合。已经提出，聚阴离子可在矿化前沿降解，以释放钙离子以与可利用的碳酸根或磷酸根离子沉淀。但是，这项研究表明，聚阴离子不会降解。基本上所有PS-1和PS-2最终都会与矿物质相一起分泌到球囊中。矿物质离子和聚阴离子分泌的动力学与聚阴离子介导的钙转运一致。然而，钙与聚阴离子螯合和释放的方式仍然不清楚。 [参考：15]

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