De La Rosa J, Ostrowski J, Hryniewicz M M, Kredich N M, Kotb M, LeGros H L, Valentine M, Geller A M
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
J Biol Chem. 1995 Sep 15;270(37):21860-8. doi: 10.1074/jbc.270.37.21860.
Human lymphocyte methionine adenosyltransferase (HuLy MAT) consists of heterologous subunits alpha and beta. The cDNA sequence of the alpha subunit of HuLy MAT from Jurkat leukemic T cells was identical to that of the human kidney alpha subunit and highly homologous to the sequence of the extrahepatic MAT from other sources. The 3'-untranslated sequence was found to be highly conserved, suggesting that it may be important in regulating the expression of MAT. The extrahepatic alpha subunit unit of MAT was found to be expressed also in human liver, and no differences were found in the sequence of the alpha subunit from normal and malignant T cells. The sequence of two unspliced introns found in the cDNA clones from the Jurkat library enabled us to isolate genomic clones harboring the human extrahepatic alpha subunit gene and to localize it to the centromere on chromosome arm 2p, an area that corresponds to band 2p11.2. Expression of the alpha subunit cDNA in Escherichia coli yielded two peptides with the immunoreactivity and mobilities of authentic alpha/alpha' subunits from HuLy. The Km of the recombinant alpha subunit was 80 microM, which is 20-fold higher than found for the (alpha alpha')x beta y holoenzyme purified from leukemic lymphocytes and 4-10-fold higher than found for the normal lymphocyte enzyme. The data suggest that the alpha/alpha' subunits mediate the enzyme catalytic activity and that the beta subunit may be a regulatory subunit of extrahepatic MAT.
人淋巴细胞蛋氨酸腺苷转移酶（HuLy MAT）由异源亚基α和β组成。来自Jurkat白血病T细胞的HuLy MATα亚基的cDNA序列与人类肾脏α亚基的序列相同，并且与其他来源的肝外MAT序列高度同源。发现3'-非翻译序列高度保守，这表明它可能在调节MAT的表达中起重要作用。还发现MAT的肝外α亚基在人肝脏中也有表达，并且在正常和恶性T细胞的α亚基序列中未发现差异。从Jurkat文库的cDNA克隆中发现的两个未剪接内含子的序列使我们能够分离出携带人类肝外α亚基基因的基因组克隆，并将其定位到染色体臂2p的着丝粒上，该区域对应于2p11.2带。α亚基cDNA在大肠杆菌中的表达产生了两种具有来自HuLy的真实α/α'亚基的免疫反应性和迁移率的肽。重组α亚基的Km为80μM，比从白血病淋巴细胞中纯化的（αα'）xβy全酶高20倍，比正常淋巴细胞酶高4至10倍。数据表明α/α'亚基介导酶的催化活性，并且β亚基可能是肝外MAT的调节亚基。
