後突觸質密區(postsynaptic density, 簡稱PSD)是由後突觸膜(postsynaptic membrane)下方由超過三十多種蛋白質聚集成的結構。
根據PSD的蛋白質組成與所在位置，可以推測PSD與神經受器聚集、神經訊息傳導、突觸結構以及神經可塑性有密切的相關性。以往使用的純化方法會增加PSD內雙硫鍵的生成，使其結構緊密穩固，以致無法用一般的化學方法分析內部的蛋白質組成。本實驗在鼠腦PSD的純化過程中分別加iodoacetamide (修飾PSD中的自由硫氫基；所得到的PSD稱為CM-PSD)、dithioerythritol (DTE, 切斷暴露在外的雙硫鍵；所得到的PSD稱為DTE-PSD)來減少純化過程中隨機生成的雙硫鍵。

對PSD的產率、主要組成蛋白質鑑定與主要組成蛋白質的相對含量的分析結果顯示，iodoacetamide與DTE不會對鼠腦中PSD的組成蛋白質造成影響。再使用不同藥劑 (如urea、guanidine-HCl、DOC與glycine/phosphoric acid) 處理PSD，並以蔗糖濃度梯度離心分析經此處理所產生的小分子，結果顯示DTE-PSD與 CM-PSD結構較鬆散，比PSD容易被藥劑打散。最後利用電子顯微鏡觀察，發現DTE-PSD與 CM-PSD呈現鬆散網狀結構，而PSD的結構卻相當緊密。這些現象與豬腦中純化出的PSD (Lai et al., 1998) 相同，顯示鼠腦PSD的純化過程中，也因蛋白質暴露在氧化環境中，而增加蛋白質間雙硫鍵，使PSD聚集成緊密的大分子結構。藉由加入IAA與DTE的方式純化鼠腦PSD，得到雙硫鍵含量較少，且結構較鬆散的PSD。

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