李春霞,嚴(yán)岱原,倪靜,郭子葉,蔡春爾,何培民
上海海洋大學(xué) 水產(chǎn)與生命學(xué)院,上海 201306
壇紫菜藻紅蛋白的規(guī)?;苽?/p>
李春霞,嚴(yán)岱原,倪靜,郭子葉,蔡春爾,何培民
上海海洋大學(xué) 水產(chǎn)與生命學(xué)院,上海 201306
為了優(yōu)化壇紫菜粗提工藝以減輕純化的壓力,研究了我國主要經(jīng)濟(jì)紅藻之一壇紫菜藻紅蛋白大規(guī)模制備方法。實驗采用“溶脹+組織搗碎”法破碎壇紫菜葉狀體細(xì)胞,對比了多次硫酸銨梯度鹽析對破碎液中藻紅蛋白的影響,并進(jìn)一步用羥基磷灰石層析制備藻紅蛋白,最后對所得蛋白做了光譜和電泳鑒定。結(jié)果表明,經(jīng)過 4次鹽析,藻紅蛋白吸收光譜純度達(dá)到0.9 (A564/A280),每次的最佳鹽析濃度分別為15%、50%、10%和40%;7 kg陰干紫菜經(jīng)過4次鹽析和1次羥基磷灰石層析后可獲得507.82 mg藻紅蛋白 (A564/A280>3.2),為進(jìn)一步研究規(guī)模高效分離純化藻紅蛋白提供了參考。
壇紫菜,藻紅蛋白,梯度鹽析,羥基磷灰石層析
Abstract:We developed large-scale preparation of phycoerythrin from Porphyra haitanensis, a main economic red algae in China. Firstly, P. haitanensis thallus was broken by using “swelling and smash” method. Then times of grads ammonium sulfate precipitation applied to the crude extraction were compared. Desalted solution was further purified with one-step chromatography using hydroxyapatite and properties on spectrum and molecular weight were identified finally. The results indicated that after four times of ammonium sulfate precipitation (15%, 50%, 10% and 40%), the absorption spectrum purity of P. haitanensis achieved 0.9(A564/A280), and 507.82 mg phycoerythrin (A564/A280>3.2) was obtained from 7 kg fresh algae after further hydroxyapatite chromatography. This research provides a potential way for preparation of phycoerythrin in large sclae.
Keywords:Porphyra haitanensis, phycoerythrin, step-precipitation, hydroxyapatite chromatography
藻膽蛋白為藻類吸收、傳遞光能的天線色素, 存在于藍(lán)藻、紅藻、隱藻和甲藻中,包括藻紅蛋白(PE)、藻藍(lán)蛋白 (PC)、別藻藍(lán)蛋白 (APC) 和藻紅藍(lán)蛋白 (PEC)[1]。藻膽蛋白顏色鮮艷,并具有抗癌、抗病毒、抗氧化、促進(jìn)血細(xì)胞再生等功效,在食用天然色素、保健食品、生物化學(xué)、熒光免疫和細(xì)胞學(xué)實驗檢測試劑等方面應(yīng)用廣泛[2-4]。
藻膽蛋白制備的常規(guī)方法主要包括藻體破碎,蛋白粗提和蛋白純化3個步驟[5],不同方法使用效果因原料而異[6],且純化階段成本高、時間長、產(chǎn)率低,是制約整個流程的瓶頸。廣泛的應(yīng)用價值和繁瑣的制備工藝使得該類蛋白的價格一直居高不下[7]。
壇紫菜Porphyra haitanensis含有豐富的PE,又是我國最主要的栽培經(jīng)濟(jì)藻類之一,還是唯一原產(chǎn)自我國的紫菜。因此從壇紫菜中提取純化PE,具有原料、價格上的優(yōu)勢。本研究旨在通過優(yōu)化壇紫菜PE粗提工藝以減輕純化的壓力,并嘗試大規(guī)模制備較高純度的PE。
壇紫菜葉狀體于2010年1月采自我國3大紫菜產(chǎn)區(qū)之一福建省福鼎市。藻體用清潔海水洗凈,10 ℃下陰干后,密封置于?20 ℃冰箱保存?zhèn)溆谩?/p>
Supra 22k高速冷凍離心機(jī)為Hanil Science公司產(chǎn)品;Ultrospec 2000紫外分光光度計為Pharmacia Biotech公司產(chǎn)品;EPS 601電泳儀為 Amersham Biosciences公司產(chǎn)品;F-4500熒光分光光度計為Hitachi公司產(chǎn)品。
常規(guī)化學(xué)藥品 (試劑純) 購自國藥集團(tuán)。
稱取400 g凍干壇紫菜,加2 000 mL磷酸鈉緩沖液 (pH 6.8,含1 mmol/L EDTA) 浸泡,4 ℃存放36 h,組織搗碎。搗碎液在4 ℃、10 000×g離心20 min,取上清,為藻膽蛋白破碎液。
取藻膽蛋白破碎液75 mL,分3管,每管25 mL,分別加至15%、20%、25%飽和度。4 ℃靜置8 h,10 000×g離心 20 min,取上清液測量體積和吸光值。確定最佳鹽析飽和度,將剩余搗碎液用該飽和度鹽析。
取第1次鹽析上清80 mL,分4管,每管20 mL,分別加至45%、50%、55%、60%飽和度。4 ℃靜置8 h,10 000×g 離心20 min,沉淀用適量緩沖液溶解后測體積和吸光值。確定最佳鹽析飽和度,將剩余第1次鹽析液用該飽和度鹽析。
取第2次鹽析溶解液60 mL,分3管,每管20 mL,分別加至5%、10%、15%飽和度。4 ℃靜置8 h,10 000×g離心20 min,取上清液測量體積和吸光值。確定最佳鹽析飽和度,將剩余第 2次鹽析液用該飽和度鹽析。
取第3次鹽析的上清80 mL,分4管,每管20 mL,分別加至35%、40%、45%、50%飽和度。4 ℃靜置8 h,10 000×g離心20 min,取沉淀,沉淀用適量緩沖液溶解后測體積和吸光值。確定最佳鹽析飽和度,將剩余第3次鹽析液用該飽和度鹽析。
取7 kg陰干壇紫菜搗碎,參照上述鹽析梯度制備鹽析液,再用Sephadex G-25脫鹽,上樣于預(yù)平衡的自制羥基磷灰石層析柱,緩沖液梯度洗脫,洗脫液測純度和產(chǎn)率。
對純化所得的壇紫菜 PE進(jìn)行光譜鑒定和電泳鑒定。光譜鑒定掃描了紫外吸收光譜和熒光發(fā)色光譜。用Native-PAGE和SDS-PAGE測定蛋白四級結(jié)構(gòu)和三級結(jié)構(gòu)的分子量,兩種電泳均分別用醋酸鋅和考馬斯亮藍(lán)染色。
藻膽蛋白吸收光譜純度計算參考 Siegelman等[8]的方法。
藻膽蛋白含量計算參考高洪峰等[9]的方法。
在不同的硫酸銨飽和度中,壇紫菜藻紅蛋白的純度和含量不同。第1次鹽析中,當(dāng)飽和度為15%時,PE的純化效果最佳,純度為0.29,得率為80%。第 2次鹽析中,當(dāng)飽和度為 50%時純化效果最佳,PE純度達(dá)到0.76,得率為74.%。第3次鹽析中,當(dāng)飽和度為10%時純化效果最佳,PE的純度為0.82,得率為95%。第4次鹽析中,當(dāng)飽和度為40%時純化效果最佳,PE的純度為0.93,得率為87%。4次鹽析結(jié)果如圖1~4所示。
圖1 壇紫菜第1次鹽析效果Fig. 1 Effect of 1st crude salting out.
圖2 壇紫菜第2次鹽析結(jié)果Fig. 2 Effect of 2nd crude salting out.
圖3 壇紫菜第3次鹽析結(jié)果Fig. 3 Effect of 3rd crude salting out.
圖4 壇紫菜第4次鹽析結(jié)果Fig. 4 Effect of 4th crude salting out.
7 kg陰干壇紫菜經(jīng)過搗碎、多次鹽析、脫鹽、及一次層析后,得到508 mg PE (A564/A280>3.2)。隨著純化流程的進(jìn)行,壇紫菜藻紅蛋白的純度依次上升,在一步羥基磷灰石層析后,藻紅蛋白的純度由層析前的0.95升高至3.65,得率由65%下降為10.6% (圖 5)。
圖5 新鮮壇紫菜純化結(jié)果Fig. 5 Results of purification from fresh Porphyra haitanensis. 1: crude extract; 2?5: extract after 1st, 2nd, 3rd, 4th saltout, repectively; 6: extract after desalting; 7: purified PE after chromatography.
層析所得壇紫菜PE的紫外吸收光譜中在497 nm和 566 nm處各有一個吸收峰 (λmax=566 nm),在538 nm處有一肩峰 (圖6),是典型的R-PE吸收峰特征[10]。對壇紫菜PE進(jìn)行熒光掃描,激發(fā)波波長介于300~600 nm (圖7),其中用561 nm光激發(fā)時得到的發(fā)射波的峰值最大,此發(fā)射峰的波長為580 nm (圖 8),是典型的 R-PE發(fā)射峰特征[11]。PE Native-PAGE顯示蛋白的四級結(jié)構(gòu)分子量約為120 kDa (圖9 1a,1b),SDS-PAGE顯示PE的三級結(jié)構(gòu)含有兩種亞基,分子量分別約為18 kDa和21 kDa(圖9 2a,2b),推測為α亞基和β亞基。由于PE為α、β亞基的多聚體,即 (αβ)n,本實驗所得PE的四級結(jié)構(gòu)為 (αβ)3。
圖6 壇紫菜PE吸收光譜Fig. 6 Absorption spectra of PE from Porphyra haitanensis.
圖7 壇紫菜PE熒光掃描3D圖譜Fig. 7 3D fluorescence spectrum of PE from Porphyra haitanensis. EX means exciting wavelength , and EM is equal to emission wavelength.
圖8 壇紫菜PE熒光發(fā)射圖譜Fig. 8 Emission spectrum of PE from Porphyra haitanensis.EX means exciting wavelength , and EM is equal to emission wavelength.
圖9 壇紫菜PE電泳鑒定圖譜Fig. 9 Electrophoresis of PE from Porphyra haitanensis. The purified PE was examined by Native-PAGE and SDS-PAGE.(1a) Fluorescent bands of the R-PE chromophore-carrying subunits exhibited under ultraviolet light at 365 nm after the gel was stained with 0.2 mol/L zinc acetate in Native-PAGE. (1b)Polypeptide bands of the R-PE showed by Coomassie Blue G-250 staining in Native-PAGE. (2a) Bands after zinc acetate staining in SDS-PAGE. (2b) Bands after Coomassie Blue G-250 staining in SDS-PAGE.
為了減輕藻膽蛋白規(guī)模制備時純化的壓力,改進(jìn)蛋白粗提工藝是方法之一。藻膽蛋白粗提制備中最常用的是硫酸銨鹽析法。目前主要有3種:1) 一步沉淀法,如將紅毛藻粗提液加至60%飽和度,得到純度0.42的PE[12]。2) 分步沉淀法,如以新鮮藍(lán)藻或紅藻為對象,用25%、35%和60%飽和度分步沉淀出PE、PC和APC[8];但30%和50%飽和度無法將純頂螺旋藻PC和APC分開[13]。3) 分段梯度鹽析法,如以純頂螺旋藻Sp (NS)-90020為對象,先用25%飽和度沉淀雜質(zhì),再以55%沉淀目標(biāo)蛋白,沉淀溶解后逐漸縮小硫酸銨濃度區(qū)域。經(jīng)過 9次鹽析,PC純度達(dá)到3.7,而APC純度為1.1[14]。本實驗結(jié)果顯示,前2種方法無法得到較高純度的PE粗提液 (圖1,2)。第3種方法鹽析次數(shù)太多,不僅費(fèi)時費(fèi)力,且其中28%~32%和35%~48%鹽析段過于狹窄,不易把握。
本實驗經(jīng)過 4次硫酸銨鹽析后,粗提液中 PE的純度由破碎液中的 0.29提高為 0.93,產(chǎn)率降為49%。該方法是對鹽析次數(shù)和鹽析藥品用量的平衡,既提高了純度,保證了得率,又降低了人力和經(jīng)濟(jì)成本。
對于藻膽蛋白規(guī)模純化前人有不少研究,如采用 DEAE瓊脂糖凝膠層析純化 550 g銅綠微囊藻Microcystis aeruginosa得到33 g純度3.4的PC和2.3 g純度4的APC[15],采用疏水層析純化700 g龍須菜 Gracilaria verrucosa得到 98 mg純度 4.4的PE[16],純化550 g掌狀紅皮藻Palmaria palmata得到67 mg純度3.5的PE[17],可見不同的原料其產(chǎn)率相差很大。
而壇紫菜的規(guī)模提純卻未見報道,本實驗采用7 000 g新鮮壇紫菜在純化時只過一次羥基磷灰石柱即可獲得508 mg純度大于3.2的PE,省時省力。且HA的成本低,適合放大。
目前雖然海洋經(jīng)濟(jì)在中國國民經(jīng)濟(jì)中的地位不斷上升,但海邊的漁民卻面臨漁業(yè)資源日趨衰竭、轉(zhuǎn)產(chǎn)轉(zhuǎn)業(yè)困難等問題。而壇紫菜PE生產(chǎn)規(guī)模的擴(kuò)大需要原料的大量供應(yīng),這為海邊的紫菜養(yǎng)殖戶開辟了新的市場渠道,有利于提高農(nóng)民收入。紫菜養(yǎng)殖不僅可為漁民帶來效益,也有利于凈化海區(qū)環(huán)境。條斑紫菜治理海區(qū)富營養(yǎng)化的實驗證明紫菜養(yǎng)殖可大量去除氮、磷元素[18],栽培期間規(guī)模化文蛤養(yǎng)殖未發(fā)生死亡現(xiàn)象,表明紫菜栽培去富營養(yǎng)化作用和生態(tài)修復(fù)功能十分明顯。
由于使用了廉價的經(jīng)濟(jì)海藻作為原料 (壇紫菜市價6元/kg),簡單和低成本的粗提工藝 (硫酸銨市價 16元/kg),自制的層析填料 (HA),加之較高的蛋白產(chǎn)率和純度,使得本方法具有較高的經(jīng)濟(jì)效益及規(guī)模可持續(xù)擴(kuò)大的潛力。因此使用本方法能夠在生產(chǎn)出高附加值藻膽蛋白的同時,也能為海區(qū)的漁民提供就業(yè)渠道,還能為治理海區(qū)的污染作出貢獻(xiàn),兼經(jīng)濟(jì)、社會、生態(tài)效益于一體。
致謝:感謝上海海洋大學(xué)嚴(yán)興洪老師提供的壇紫菜。
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Scale-up preparation of phycoerythrin from Porphyra haitanensis
Chunxia Li, Daiyuan Yan, Jing Ni, Ziye Guo, Chun’er Cai, and Peimin He
Aqual-life Science and Technology College, Shanghai Ocean University, Shanghai 201306, China
Received: June 23, 2010; Accepted: October 18, 2010
Supported by: National High Technology Research and Development Program of China (863 Program) (Nos. 2006AA10Z323, 2007AA09Z406),Shanghai Education Commission Key Discipline Program (No. S30701).
Corresponding author: Peimin He. Tel: +86-21-61900423; E-mail: pmhe@shou.edu.cn
國家高技術(shù)研究發(fā)展計劃 (863計劃) (Nos. 2006AA10Z323, 2007AA09Z406),上海市教委優(yōu)勢 (重點) 學(xué)科項目 (No. S30701) 資助。