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生物學中的鋅

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A twisted band, with one side painted blue and another gray. Its two ends are connected through some chemical species to a green atom (zinc).
鋅指有助於讀取DNA序列

鋅是人類[1][2][3]、其他動物[4]、植物[5]微生物中所不能缺少的微量元素[6] 它在超過300中酶和1000種轉錄因子的功能中發揮着至關重要的作用,[3] 並在金屬硫蛋白中儲存和轉移.[7][8] 它是人體中含量僅次於鐵的第二大微量金屬,也是所有酶類中出現的唯一金屬。[5][3]

在蛋白質中,鋅離子通常與天冬氨酸穀氨酸半胱氨酸組氨酸的氨基酸側鏈配位。想要理論性地描述和計算這種鋅在蛋白質(以及其他過渡金屬)中的結合是困難的。[9]

整個人體中分布着大約2-4克鋅。[10]大多數鋅存在於大腦、肌肉、骨骼、腎臟和肝臟中,其中前列腺和眼睛部分的濃度最高。[11]精液特別富含鋅,鋅是前列腺功能和生殖器官生長的關鍵因素。[12]

身體的鋅穩態主要由腸道控制。在這裡,ZIP4,尤其是TRPM7與出生後生活所必需的腸道鋅攝取有關。[13][14]

在人類中,鋅的生物學作用無處不在。[15][2]它與範圍廣泛的有機配體相互作用,[15]並在 RNA 和 DNA 的代謝、信號轉導和基因表達中發揮作用。它還調節細胞凋亡。 2015 年的一篇綜述表明,大約 10%的人類蛋白質能夠結合鋅,[16]此外還有數百種蛋白質運輸和運輸鋅;在擬南芥植物中進行的一項研究發現了 2367 種與鋅相關的蛋白質。[5]

在大腦中,鋅被穀氨酸能神經元儲存在特定的突觸小泡中,可以調節神經元的興奮性。[2][3][17] 它在突觸可塑性和學習中起着關鍵作用。[2][18]鋅穩態在中樞神經系統的功能調節中也起着關鍵作用。[2][17][3]中樞神經系統鋅穩態失調導致突觸鋅濃度過高被認為是通過線粒體氧化應激誘導的神經毒性(例如,通過破壞電子傳遞鏈中涉及的某些酶,包括複合物 I 、複合物 III和α-酮戊二酸脫氫酶)、鈣穩態失調、穀氨酸能神經元興奮性毒性和干擾神經元內信號轉導。[2][19]L-和D-組氨酸促進腦鋅攝取。[20]SLC30A3是參與腦鋅穩態的主要鋅轉運體。[2]

[編輯]
Interconnected stripes, mostly of yellow and blue color with a few red segments.
碳酸酐酶II的帶狀圖,中心可見鋅原子
A twisted band, with one side painted blue and another gray. Its two ends are connected through some chemical species to a green atom (zinc).
鋅指有助於讀取DNA序列

鋅是一種有效的路易斯酸,使其成為羥基化和其他酶促反應中有用的催化劑。[21]這種金屬還具有靈活的配位幾何結構,這使得使用它的蛋白質能夠快速改變構象以進行生物反應。[22]含鋅酶的兩個例子是碳酸酐酶和羧肽酶,它們對二氧化碳的調節和蛋白質的消化至關重要。[23]

在脊椎動物的血液中,碳酸酐酶將CO
2
轉化為碳酸氫鹽,同樣的酶將碳酸氫鹽轉化為CO
2
通過肺呼出。[24]如果沒有這種酶,在正常血液pH值為7或需要pH值為10或更高時[25],這種轉化的發生速度會慢大約一百萬倍。[26]非相關的β-碳酸酐酶是植物葉片形成、吲哚乙酸生長素)合成和酒精發酵所必需的。[27]

羧肽酶在蛋白質消化過程中切割肽鍵。在末端肽和連接到鋅上的C=O基團之間形成配位共價鍵,使碳帶正電荷。這有助於在鋅附近的酶上形成一個疏水團,吸引被消化蛋白質的非極性部分。[23]

信號

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鋅已被公認為信使,能夠激活信號通路。其中許多途徑為癌症的異常生長提供了驅動力。它們可以通過ZIP傳輸器作為目標。[28]

其他蛋白質

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鋅在鋅指結構域、扭曲結構和簇狀結構中起純粹的結構作用。[29]鋅指是某些轉錄因子的一部分,轉錄因子是在DNA複製和轉錄過程中識別DNA鹼基序列的蛋白質。每個鋅指中的九個或十個Zn2+
離子通過與轉錄因子中的四個氨基酸協同結合,有助於維持鋅指的結構。[26]

血漿中,鋅與白蛋白(60%,低親和力)和轉鐵蛋白(10%)結合併由其轉運。[10]因為轉鐵蛋白也轉運鐵,過多的鐵會減少鋅的吸收,反之亦然。銅也存在類似的拮抗作用。[30]無論鋅攝入量如何,血漿中鋅的濃度都保持相對恆定。[21] 唾液腺、前列腺、免疫系統和腸道中的細胞使用鋅信號與其他細胞進行通信。[31]

鋅可能在微生物中以金屬硫蛋白的形式儲存,也可能儲存在動物的腸道或肝臟中。[32]腸道細胞中的金屬硫蛋白能夠調節約15-40%的鋅吸收。[33]然而,攝入過少或過多的鋅都可能有害;過量的鋅尤其會影響銅的吸收,因為金屬硫蛋白可以同時吸收這兩種金屬。[34]

人類多巴胺轉運體含有一個高親和力的細胞外鋅結合位點,當鋅結合時,會抑制多巴胺的再攝取,並在離體試驗中增強苯丙胺誘導的多巴胺外流。[35][36][37]而人類血清素轉運體去甲腎上腺素轉運體則不含有鋅結合位點。[37]一些EF-hand鈣結合蛋白,如S100或NCS-1,也能夠結合鋅離子。[38]

土壤修復

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Calluna, EricaVaccinium属的植物能够在含锌的金属质土壤中生长,这是因为杜鹃花菌根真菌的作用阻止了有毒离子的转运。[39]

農業

[編輯]

缺鋅似乎是作物植物中最常見的微量元素缺乏,尤其在高pH值的土壤中更為普遍。[40]在土耳其和印度的大約一半耕地、中國的三分之一耕地以及大部分西澳大利亞的耕地中,存在着缺鋅的土壤。這些地區已報道通過鋅施肥可以獲得顯著的效果。[5] 在缺鋅的土壤中生長的植物更容易受到病害的侵害。鋅主要通過岩石風化添加到土壤中,但人類通過燃燒化石燃料、礦山廢棄物、磷酸鹽肥料、殺蟲劑(磷化鋅)、石灰石、肥料、污水污泥以及鍍鋅表面的顆粒等方式添加了鋅。過量的鋅對植物有毒性,儘管鋅中毒的範圍遠不及鋅缺乏普遍。[5]


本文基於該詞條的英語維基百科

參考文獻

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