The speEspeD operon of Escherichia coli. Formation and processing of a proenzyme form of S-adenosylmethionine decarboxylase.
The speEspeD operon of Escherichia coli. Formation and processing of a proenzyme form of S-adenosylmethionine decarboxylase.
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大肠杆菌的高速操纵子。
DOI：
10.1016/s0021-9258(18)47692-2
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
H. Tabor
中科院分区：
文献类型：
--
作者：
C. W. Tabor;H. Tabor
我们先前已经表明，S-腺苷甲硫氨酸脱羧酶的基因（speD）是操纵子的一部分，该操纵子还包含亚精胺合酶的基因（speE）（塔博尔，C. W.，塔博尔，H.，和Xie，Q.- W.等人（1986）Proc. Acad. Sci.联合S. A. 83，6040-6044）。我们现在已经确定了这种操纵子的核苷酸序列，并发现speD编码的多肽Mr = 30，400，这比纯化酶的亚基大小大得多。我们的研究表明，S-腺苷甲硫氨酸脱羧酶首先形成为Mr = 30，400的多肽，然后该酶原在Lys 111-Ser 112肽键处裂解，形成Mr = 12，400的亚基和Mr = 18，000的亚基。后一个亚基含有我们先前显示的酶活性所需的异戊酰部分。两种亚基都存在于纯化的酶中。这些结论是基于（i）用含有speD+质粒的菌株进行的脉冲追踪实验，该质粒显示了酶原和酶亚基之间的底物-产物关系，（ii）S-腺苷甲硫氨酸脱羧酶的酶原形式的氨基酸序列，（来源于speD基因的核苷酸序列），和（iii）将该酶原序列与Anton和Kutny（Anton，D. L.，和Kutny，R.（1987）J.Biol.Chem.262，2817-2822）。
We have previously shown that the gene (speD) for S-adenosylmethionine decarboxylase is part of an operon that also contains the gene (speE) for spermidine synthase (Tabor, C. W., Tabor, H., and Xie, Q.-W. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 6040-6044). We have now determined the nucleotide sequence of this operon and have found that speD codes for a polypeptide of Mr = 30,400, which is considerably greater than the subunit size of the purified enzyme. Our studies show that S-adenosylmethionine decarboxylase is first formed as a Mr = 30,400 polypeptide and that this proenzyme is then cleaved at the Lys111-Ser112 peptide bond to form a Mr = 12,400 subunit and a Mr = 18,000 subunit. The latter subunit contains the pyruvoyl moiety that we previously showed is required for enzymatic activity. Both subunits are present in the purified enzyme. These conclusions are based on (i) pulse-chase experiments with a strain containing a speD+ plasmid which showed a precursor-product relationship between the proenzyme and the enzyme subunits, (ii) the amino acid sequence of the proenzyme form of S-adenosylmethionine decarboxylase (derived from the nucleotide sequence of the speD gene), and (iii) comparison of this sequence of the proenzyme with the N-terminal amino acid sequences of the two subunits of the purified enzyme reported by Anton and Kutny (Anton, D. L., and Kutny, R. (1987) J. Biol. Chem. 262, 2817-2822).