Putrescine biosynthesis in mammalian tissues
Putrescine biosynthesis in mammalian tissues
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DOI：
10.1042/bj20040035
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发表时间：
2004-05-01
影响因子：
4.1
通讯作者：
Pegg, AE
中科院分区：
文献类型：
--
作者：
Coleman, CS;Hu, GR;Pegg, AE
L-鸟氨酸脱羧酶在哺乳动物中提供腐胺的从头生物合成。涉及ADC（L-精氨酸脱羧酶）的生成腐胺的替代途径存在于非哺乳动物生物体中。已经表明，ADC介导的途径可以在哺乳动物组织中通过胍丁胺产生腐胺。已发表的哺乳动物ADC的证据基于（i）使用线粒体提取物的试验，显示从[1-C-14]精氨酸产生O-14（2）和（ii）已声称代表ADC的克隆cDNA序列。我们重新调查了这一证据，但未能找到任何支持哺乳动物ADC的证据。在存在或不存在精氨酸代谢途径抑制剂的情况下，使用L-[U-C-14]-精氨酸测定使用甲泛葡胺/Percoll密度梯度从新鲜分离的啮齿动物肝脏和肾脏制备的线粒体提取物的ADC活性。虽然（CO2）-C-14产生了大量的，没有标记胍丁胺或腐胺被检测到。[C-14]添加到肝脏提取物中的胍丁胺未显著降解，表明源自推定ADC活性的任何胍丁胺均未因进一步代谢而损失。使用非哺乳动物ADC序列对当前基因组数据库的广泛搜索没有鉴定出可行的候选ADC基因。其中一个推定的哺乳动物ADC序列似乎来源于细菌，另一个缺乏脱羧酶活性所必需的几个残基。这些结果表明，从[1-C-14]精氨酸释放的（CO2）-C-14不是哺乳动物ADC的充分证据。虽然胍丁胺是哺乳动物细胞的已知成分，但它可以从饮食中转运。因此L-鸟氨酸脱羧酶仍然是哺乳动物中腐胺从头生物合成的唯一确定途径。
L-Ornithine decarboxylase provides de novo putrescine biosynthesis in mammals. Alternative pathways to generate putrescine that involve ADC (L-arginine decarboxylase) occur in non-mammalian organisms. It has been suggested that an ADC-mediated pathway May generate putrescine via agmatine in mammalian tissues. Published evidence for a mammalian ADC is based on (i) assays using mitochondrial extracts showing production of O-14(2) from [1-C-14]arginine and (ii) cloned cDNA sequences that have been claimed to represent ADC. We have reinvestigated this evidence and were unable to find any evidence supporting a mammalian ADC. Mitochondrial extracts prepared from freshly isolated rodent liver and kidney using a metrizamide/Percoll density gradient were assayed for ADC activity using L-[U- C-14]- arginine in the presence or absence of arginine metabolic pathway inhibitors. Although (CO2)-C-14 was produced in substantial amounts, no labelled agmatine or putrescine was detected. [C-14]Agmatine added to liver extracts was not degraded significantly indicating that any agmatine derived from a putative ADC activity was not lost due to further metabolism. Extensive searches of current genome databases using non-mammalian ADC sequences did not identify a viable candidate ADC gene. One of the putative mammalian ADC sequences appears to be derived from bacteria and the other lacks several residues that are essential for decarboxylase activity. These results indicate that (CO2)-C-14, release from [1-C-14]arginine is not adequate evidence for a mammalian ADC. Although agmatine is a known constituent of mammalian cells, it can be transported from the diet. Therefore L-ornithine decarboxylase remains the only established route for de novo putrescine biosynthesis in mammals.