摘要:雄烯二酮(AD)和雄二烯二酮(ADD)是甾體激素類藥物重要的中間體,目前以微生物植物甾醇生物轉(zhuǎn)化生產(chǎn)AD(D)是研究的熱點,綜述了微生物生物轉(zhuǎn)化植物甾醇生產(chǎn)雄烯二酮的研究進(jìn)展。
關(guān)鍵詞:雄烯二酮(AD);雄二烯二酮(ADD);甾體化合物;生物轉(zhuǎn)化;Mycobacterium sp.
中圖分類號:Q939.9 文獻(xiàn)標(biāo)識碼:A 文章編號:0439-8114(2012)07-1309-03
Progress of Biotransforming Phytosterols into Androstadienedione and Androstenedione by Microorganisms
LIANG Jian-jun,WANG Wen-jun
(College of Life Science, South-Central University for Nationalities,Wuhan 430074,China)
Abstract: Androstadienedione(ADD) and androstenedione(AD) are the major compounds in the synthesis of steroid drugs. Biotransformation with microorganisms was regarded as the most promising method to produce AD(D). The advance of biotransforming phytosterol into AD(D) by microorganisms was summarized.
Key words: androstadienedione; androstenedione; phytosterol; biotransformation; Mycobacterium sp.
雄烯二酮(AD)、雄二烯二酮(ADD)是甾體激素類藥物不可替代的中間體,幾乎所有甾體激素藥物都可以以AD(D)為起始原料進(jìn)行生產(chǎn)。以廉價的甾體化合物制備AD(D)受到越來越多的重視,植物甾醇如β-谷甾醇、菜油甾醇烷和菜油甾醇等價格低廉,自發(fā)現(xiàn)分支桿菌(Mycobacterium)可以選擇性降解甾體化合物側(cè)鏈生產(chǎn)17酮-甾體化合物以來,植物甾醇已成為制備AD(D)的首選原料。
1 AD(D)生產(chǎn)的原料
采用具有甾體結(jié)構(gòu)且廉價的原料生產(chǎn)甾體類化合物,這些化合物都有甾體環(huán)戊烷多氫菲母核結(jié)構(gòu)。薯蕷皂甙在20世紀(jì)70年代以后很長的一段時期占據(jù)著主導(dǎo)地位,由于需求日增,薯芋資源日漸枯竭,其利用率較低、成本高而使得商業(yè)化利潤降低,人們開始開拓新的資源。植物甾醇主要來源于油脂的生產(chǎn)廢渣及其他工業(yè)廢物,如豆油、油菜子、制糖廢渣、工業(yè)廢物及造紙廢水[1-3]。表1列出了可利用不同甾體化合物為底物生產(chǎn)AD(D)的微生物。
2 生物轉(zhuǎn)化甾體化合物生產(chǎn)AD(D)的方法
2.1 水相中微生物生物轉(zhuǎn)化方法
甾體化合物在水中溶解度極低,限制了微生物利用其進(jìn)行生物轉(zhuǎn)化的能力。細(xì)胞壁和細(xì)胞膜作為底物進(jìn)入胞漿的屏障會極大地影響生物轉(zhuǎn)化的產(chǎn)率[8,9]。萬古霉素、氨基乙酸、卵磷脂、魚精蛋白、多粘菌素B九肽、乙胺丁醇、桿菌肽和聚乙烯亞胺等都可以引起Mycobacterium相關(guān)菌株的細(xì)胞壁缺失[8-10]。萬古霉素和氨基乙酸通過降低細(xì)胞壁上多肽的交聯(lián)度而影響肽聚糖的厚度。魚精蛋白通過改變非共價結(jié)合油脂的相關(guān)比例而影響細(xì)胞壁雙分子層的結(jié)構(gòu)完整性和流動性。
關(guān)于Tween、Triton X-100、Triton X-114和卵磷脂對植物甾醇轉(zhuǎn)化生產(chǎn)AD(D)的影響也有許多研究[4,8,11,12]。卵磷脂既不改變水溶液的界面張力也不會導(dǎo)致如使用表面活性劑Tween 80易產(chǎn)生泡沫的問題,具有良好的生物相容性,對細(xì)胞的生長沒有不利的影響,卵磷脂處理后增加了細(xì)胞膜透性,使甾體化合物側(cè)鏈降解產(chǎn)生AD(D)的比活力提高了3倍[8]。
環(huán)糊精在AD(D)生產(chǎn)方面的應(yīng)用有廣泛的報道[13-16]。環(huán)糊精可形成包埋化合物,從而有效地提高水相中不溶性有機(jī)化合物的微生物轉(zhuǎn)化能力。采用環(huán)糊精包埋植物甾醇后利用Mycobacterium sp. NRRL B-3683進(jìn)行生物轉(zhuǎn)化可以有效地提高AD(D)產(chǎn)量。Donova等[15]研究了甲基化-β-環(huán)糊精對Mycobacterium sp. VKM Ac-1816D生長、AD(D)產(chǎn)量的影響,發(fā)現(xiàn)甲基化-β-環(huán)糊精使微生物脂雙層紊亂,使得結(jié)合在細(xì)胞壁上的甾體轉(zhuǎn)化酶釋放。
2.2 兩相體系中的生物轉(zhuǎn)化方法
Flygare等[17]采用雙水相體系利用Mycobacterium sp.生物轉(zhuǎn)化膽固醇生產(chǎn)AD和ADD時,采用PEG、葡聚糖和Brij 35,PVP、葡聚糖和Brij 35以及PVP、葡聚糖和吐溫3種生物轉(zhuǎn)化體系。Stefanov等[18]用豆油、葵花子油、聚丙烯乙二醇(PPG)和硅油來增加植物甾醇的溶解度,其轉(zhuǎn)化為AD和ADD的轉(zhuǎn)化率顯著提高。Cruz等[19]研究了在有機(jī)溶劑-水兩相系統(tǒng)中不同有機(jī)溶劑對β-豆甾醇側(cè)鏈降解生產(chǎn)AD的影響,用Mycobacterium sp. NRRL B-3805生物轉(zhuǎn)化β-豆甾醇生產(chǎn)AD,在含有10 g/L酵母浸膏和磷酸緩沖液(pH 7.0)的培養(yǎng)基中獲得了比含有磷酸緩沖液(pH 7.0)、NH4Cl (2 g/L), MgSO4·7H2O (0.14 g/L)和果糖(10 g/L)的合成培養(yǎng)基更好的效果。Santos等[20]在PEG-谷氨酸鈉的雙水相體系中采用Arthrobacter simplex對氫化可的松進(jìn)行△1-脫氫作用,獲得了比PEG-羥基化淀粉或PEG-磷酸鉀雙水相體系更高的底物轉(zhuǎn)化率和微生物/甾體化合物分離效率。
2.3 濁點系統(tǒng)中的生物轉(zhuǎn)化方法
濁點系統(tǒng)(Cloud point systems,CPS)為維持微生物存活及酶活性提供了一個有效的微水相環(huán)境,被水相微囊包圍的微生物均勻地分散于富含表面活性劑的連續(xù)相中,因此底物和有機(jī)相的毒性和抑制性都顯著降低。生物轉(zhuǎn)化發(fā)生在含有微生物的水相微囊中,產(chǎn)物被萃取到表面活性劑形成的凝聚層中。Wang等[11,12]采用此方法用微生物進(jìn)行了膽固醇轉(zhuǎn)化為ADD的研究,表明采用非離子型表面活性劑Triton X-100和Triton X-114組成一個新型的兩相分配生物反應(yīng)器,在此體系中膽固醇生物轉(zhuǎn)化為ADD的效率有了較大提高。
2.4 固定化微生物的生物轉(zhuǎn)化方法
采用固定化微生物細(xì)胞進(jìn)行了甾體化合物的生物轉(zhuǎn)化[7,21]。在一個分批轉(zhuǎn)化過程中,采用活化氧化鋁載體固定化Mycobacterium sp. NRRL B-3683細(xì)胞,以1 g/L的膽固醇為底物,使得ADD每天的產(chǎn)率達(dá)到了0.19 g/L,摩爾轉(zhuǎn)化率為77%,固定化微生物的半衰期超過了45 d[5]。果膠酸鈣固定化A. simplex ATCC 6946時,相對于為固定化生物轉(zhuǎn)化過程,在水相和油相培養(yǎng)基中進(jìn)行轉(zhuǎn)化時發(fā)現(xiàn)AD轉(zhuǎn)化為ADD的效率沒有統(tǒng)計學(xué)差異[22]。Llanes等[23]研究了使用固定化Mycobacterium sp. 在有機(jī)生物轉(zhuǎn)化培養(yǎng)基中進(jìn)行豆甾醇側(cè)鏈選擇性降解的可能性,研究發(fā)現(xiàn)在Celite matrices表面存在一定的水化層對于豆甾醇轉(zhuǎn)化為AD(D)是很必要的。 Claudino等[24]研究了采用硅樹脂板和Celite為固定化Mycobacterium sp.的載體進(jìn)行豆甾醇轉(zhuǎn)化為AD,當(dāng)豆甾醇初始濃度為0.482 mmol/L,細(xì)胞濃度為1 mm板上固定1.4 mg時,AD的產(chǎn)量為0.436 mmol/L,將Mycobacterium sp.固定化在硅樹脂板上的效果要比固定在Celite上好。
2.5 微乳化和脂質(zhì)體的生物轉(zhuǎn)化體系
微乳化(MEs)相對兩相體系提供了一個傳質(zhì)面積顯著提高的方法。Stefan等[25]報道在水包油的微乳化體系中E. coli、 Saccharomyces cerevisiae和Rhodotorula minuta的細(xì)胞存活率在70%~80%之間。Malaviya等[26]采用A. simplex研究了基于微乳化體系的幾個培養(yǎng)體系對轉(zhuǎn)化的影響,在這一穩(wěn)定的MEs 體系中豆甾醇的最大溶解度高達(dá)8 g/L,在此體系中轉(zhuǎn)化2 g/L的豆甾醇得到的AD最高產(chǎn)量為465.86 mg/L。Llanes等[22]利用固定化A. simplex成功地對多薄層膠囊包埋的AD進(jìn)行了生物轉(zhuǎn)化,而在水相中轉(zhuǎn)化進(jìn)行3 h后0.63 mmol/L的AD僅有50%得以轉(zhuǎn)化,而脂質(zhì)體包埋的1 mmol/L的AD在2 h內(nèi)得以完全轉(zhuǎn)化。
3 展望
微生物生物轉(zhuǎn)化植物甾醇生產(chǎn)雄烯二酮是當(dāng)前研究的熱點,集中的研究方向應(yīng)在于獲得更加廉價和有效的生物轉(zhuǎn)化過程,主要是以下幾個方面:①選育高產(chǎn)的微生物菌種;②提高廉價底物的利用率;③轉(zhuǎn)化過程優(yōu)化;④提高轉(zhuǎn)化體系中甾體化合物的溶解度;⑤發(fā)酵過程優(yōu)化,包括很多方面的新型生物反應(yīng)器設(shè)計、培養(yǎng)基優(yōu)化、操作參數(shù)優(yōu)化、過程控制和放大培養(yǎng)等。
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