透過進食,我們能夠從食物中獲取身體所需的能量。這過程亦稱之為新陳代謝。480Please respect copyright.PENANAYI9VTIAmnp480Please respect copyright.PENANARUN4MexUIN
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有無數證據顯示,癌細胞的新陳代謝與正常的細胞有著顯著的分別。480Please respect copyright.PENANAtf3JYyASIc
正因如此,有不少科學家抱有一個信念,希望透過針對癌細胞的新陳代謝來抑止癌細胞的生長,甚至是達消滅癌細胞之效。480Please respect copyright.PENANAOv3jKwDrL2
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(圖2)半胱胺酸 (Cysteine)是氨基酸的一種,亦即是組成蛋白質的基本單元。480Please respect copyright.PENANAjKKBN8cr8e480Please respect copyright.PENANAtBBBtPSbF6
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我們可以透過直接進食來攝取Cysteine,又或者依靠肝臟將特定兩隻氨基酸(Methionine及Serine)轉化成為Cysteine供我們所用。480Please respect copyright.PENANA7cT6E5Yp3v
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有科學家嘗試從飼養癌細胞的營養液中剔除Cysteine,發覺部份癌細胞的生長速度有所減慢,而有部份的癌細胞則趨向死亡(Ref1)。480Please respect copyright.PENANAJnPZPImBm8
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(圖3)從營養液剔除Cysteine後,身體攝取Cysteine的辦法便只剩下依靠肝臟將同為氨基酸的Methionine及Serine轉化成為Cysteine。480Please respect copyright.PENANARJePIUKe6r480Please respect copyright.PENANA4heZzFsbQM
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而各種剔除Cysteine便會死亡的癌細胞的共通點,就是缺乏一隻名為5-methylthioadenosine phosphorylase(MTAP)的蛋白酶。480Please respect copyright.PENANArZsGYQ9VIi
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失去MTAP後,細胞會傾向將Methionine轉化成為一系列名為Polyamine的物質,導致身體失去製作Cysteine的手段。480Please respect copyright.PENANAQ8bEWXPXyb
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更甚的是,產生Polyamine的過程中將會產生游離基,而制衡游離基的Glutathione卻則依靠Cysteine作為原材料。480Please respect copyright.PENANAasOPEXFCZx
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因此,缺乏MTAP的癌細胞若然沒有外來Cysteine供應的話,便會因游離基數量過多而導致死亡。480Please respect copyright.PENANA4nPxdczVVv
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環觀各種癌細胞,膠質母細胞瘤(Glioblastoma)有較大的機會因基因變異而失去MTAP基因。480Please respect copyright.PENANArlRj5T3jYq
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根據上述研究結果,若癌症病人的癌細胞證實缺乏MTAP基因的話,在餐單中剔除進食Cysteine氨基酸或許是一個副作用相對上為微的理性選擇。480Please respect copyright.PENANADCLydLKQSz
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Ref1:https://www.nature.com/articles/s42255-020-0253-2