紅藻龍鬚菜Gracilaria tenuistipitata（GT），經蛋白酶（酵素/受質比1:100）在37℃進行15小時水解所得萃取物（GT extract），再分別以硫酸銨濃度0-20%、20-40%、40-60%及60-80%鹽析沈澱出四蛋白質萃取物（GT protein extracts, GTPE），分別稱GTPE2、GTPE4、GTPE6與GTPE8，再經透析與冷凍乾燥後，以蛋白質電泳分析GT extract與此四種鹽析所得的GTPEs分子量分布，並探討此四種GTPE之DPPH與超氧陰離子自由基的清除活性以及GTPE對質體DNA保護降低自由基氧化傷害的的效應。實驗結果顯示四種GTPEs分子量多在30 kDa以下，主要分子量範圍為20.1 -14.4 kDa間及14.4 kDa以下。抗自由基活性測試發現，GTPE4與GTPE6具有較顯著活性。這些蛋白質萃取物具有應用在食品添加物或營養補充劑的潛力。

This goal of this research is to study the antiradical properties of protein extracts from red seaweed Gracilaria tenuistipitata (GT) treated with proteinase bromelain. Bromelain was added into fresh seaweed samples (enzyme/substrate 1:100, w/w) with a pH 6.2 buffer. After 15 h enzymatic hydrolysis at 37℃, the solution containing hydrolysates was treated with various concentration ranges of ammonium sulfate (0-20%, 20-40%, 40-60%, and 60-80%) to precipitate the four GT protein extracts (GTPEs), namely GTPE2, GTPE4, GTPE6, and GTPE8. After dialysis, the GTPEs were lypholized and then electrophoresed to analyze their molecular weight distribution. In addition, the GTPEs were evaluated their free radical scavenging activities including DPPH and superoxide radicals. Moreover, the protective effect of GTPEs on plasmid DNA oxidative damage induced by free radicals was also studied.