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標題: 嗜鹽性甲烷古生菌相容質glycine betaine生合成調控與其生合成酵素 glycine N-methyltransferase的純化
The biosynthesis of glycine betaine in halophilic methanogenic archaea Methanohalophilus portucalensis FDF1 and the purification of glycine N-methyltransferase
作者: 莊旻真
Chuang, Ming-Jen
關鍵字: 相容質;halophilic methanogenic archaea;嗜鹽性甲烷古生菌;生合成調控;glycine betaine;Methanohalophilus portucalensis FDF1;glycine N-methyltransferase
出版社: 植物學系
portucalensis FDF1,會於細胞內累積glycine betaine, (-glutamine
已知相容質中glycine betaine具有最高的滲透壓保護係數,且大部份生
物都能利用glycine betaine做為相容質。為了探討glycine betaine生合
成途徑及其調控因子,我們利用Mh. portucalensis FDF1細胞萃取液分析
glycine betaine的生合成,發現必須有鉀離子存在才有glycine betaine
glycine,sarcosine,N,N-dimethylglycine及glycine betaine為基質的
實驗證實glycine betaine的生合成可由SAM提供甲基,經三次甲基化作用
由glycine?sarcosine?N, N-dimethylglycine合成glycine betaine。
sarcosine轉化成glycine betaine,但N, N-dimethylglycine會迅速轉化
成glycine betaine,而不能在胞內累積。 於純化glycine betaine生合
成酵素-glycine N-methyltransferase(GNMT)的過程中,將Mh.
portucalensis FDF1厭氧細胞萃取液通過DEAE-Sephacel陰離子交換樹脂
,並以0.1~1.0 M的鉀離子濃度梯度沖洗管柱後,在1.0 M鉀離子濃度的沖
合成sarcosine的比活性為6.12 nmole/(,約佔細胞總蛋白量的0.12
﹪,分子量約為240 kD。於SDS-PAGE電泳上發現GNMT可分成100 kD,55
kD,40 kD三個polypeptides。

Halophilic methanogen Methanohalophilus portucalensis FDF1 is
able to accumulate glycine betaine, (-glutamine, N(-acetyl-(-
lysine and potassium ion as the compatible solutes to survive in
the hypersaline environment. Among all known compatible solutes,
glycine betaine has the highest osmoprotective efficiency and
most halotolerant and halophilic organisms can accumulate it as
the compatible solutes. The anaerobic crude extract of glycine
betaine synthesizing Mh. portucalensis FDF1 were used in
accompany with (14C(-glycine or (methyl14C(-S-adenosyl-L-
methionine (SAM) to study the glycine betaine biosynthetic
pathway and its regulatory factors. Results showed that
potassium is required for the formation of glycine betaine.
Other monovalent cations, lithium or sodium, could partly or
completely substitute potassium function. Results also indicated
that SAM can be the methyl donor in the process of glycine b
etaine formation. It also confirmed that the de novo
biosynthesis of glycine betaine proceed from glycine to
sarcosine and N, N-dimethylglycine. High potassium level
enhanced the formation of glycine betaine while lower potassium
level favored the sarcosine accumulation. The glycine betaine
formation enzyme ?glycine N-methyltransferase (GNMT) was
purified by using the DEAE-Sephacel anion exchange column with
the linear gradient of potassium chloride (0.1~1.0 M) with the
crude extract of Mh. portucalensis FDF1. Elutant with 1.0 M
potassium showed the GNMT activity and later demonstrated as
purified protein by native gel electrophoresis. The estimated
molecular weight of the GNMT was about 240 kD and can be
separated into three subunits as 100 kD, 55 kD and 40 kD in
sodium dod ecyl sulfate electrophoresis. GNMT composes 0.12﹪of
the total cell protein of Mh. portucalensis FDF1 and the
specific activity of this enzyme with glycine as substrate is
6.12 nmole/(
Appears in Collections:生命科學系所

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