最近十年醫學知識更新十分快速,醫學生千萬不要認為老師懂他上課講的東西,課後還死啃共筆,得到錯誤的觀念。兩天前某位學弟問我一段Lehninger上的文字,他實在看不懂:
An aquaporin isolated from spinach is known to be “gate”-open when two critical Ser residues near the intracellular end of the channel are phosphorylated, and closed when they are dephodphorylated. Both the open and closed structures have been determined by crystallography.
Phosphorylation favors a conformation that presses two nearby Leu residues and a His residue into the channel, blocking the movement of water pass that point and effectively closing the channel.

細胞膜是由懼水性的脂質(磷脂膽固醇、醣脂等)構成,因此水分子(H2O)通過細胞膜必須經由特殊蛋白質構成的管道(Channel)如AquaporinAquaporin2000年以後寫進教科書的新知識,它的發現讓我們更加了解水分子如何通過細胞膜。上文中紅色的Phosphorylation (磷酸化)是錯誤的,正確應該是「Dephosphorylation(去磷酸化)」。我找出2006年刊登在Nature 的文章:
Structural mechanism of plant aquaporin gatinghttps://www.nature.com/articles/nature04316

Aquaporin spinach.2    
b: Serine Dephosphorylation兩個Leu “Two doors of the gate”一個His  “The latch of the gate” 阻擋水分子(紅色)通過。
c: Serine PhosphorylationHis-latch is released, and Leu-doors are open. 水分子可通過Aquaporin channel.  
d: Aquaporin受強烈刺激後(如胞膜內外離子濃度差的壓力或細胞受大量激素的作用) 整個Channel大開讓大批水分子通過。

讀原文書時,讀到不懂的地方,有時要相信自己沒讀錯,是作者寫錯了。經典教科書都會寫錯,老師上課也一定會教錯,學生寫的共筆更是錯誤連篇。

上面雖然是植物的Aquaporin但人體細胞遍佈Aquaporin腎小管要吸收水份,大腸也要吸收水份,肺泡細胞必須移除肺泡內過多的水分,氧氣才能順利通過肺泡細胞。現在的生理學已經進入生化層次,未來不懂生化的醫師真的只能用  無知來形容。



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