5-Formyltetrahydrofolate is an inhibitory but well tolerated metabolite in Arabidopsis leaves
5-Formyltetrahydrofolate is an inhibitory but well tolerated metabolite in Arabidopsis leaves
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DOI：
10.1074/jbc.m503106200
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发表时间：
2005-07-15
影响因子：
4.8
通讯作者：
Hanson, AD
中科院分区：
文献类型：
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作者：
Goyer, A;Collakova, E;Hanson, AD
甲酰基四氢叶酸（Formyltetrahydrofolate, 5-CHO-THF）通过丝氨酸羟甲基转移酶（SHMT）的二次催化活性形成，并在体外强烈抑制SHMT和其他叶酸依赖酶。唯一已知的代谢5- cho - thf的酶是5- cho - thf环寡化酶（5- fcl），它催化其转化为5,10-甲基四氢叶酸。由于5-FCL在植物中是线粒体的，而线粒体SHMT是光呼吸的核心，我们研究了在光呼吸（30和370 μ mol CO2 mol(-1)）和非光呼吸（3200 μ mol CO2 mol(-1)）条件下拟南芥5-FCL基因（At5g13050）插入突变的影响。在二氧化碳浓度为370 μ mol mol（-1）时，该突变只产生轻微的可见效应，使生长速度降低20%，开花时间推迟1周。然而，突变在所有条件下都使叶片5- cho - thf水平增加了一倍，在光呼吸条件下，10-甲酰基-/5,10-甲基四氢叶酸池增加了四倍（无法进行分析区分）。当CO2浓度为370 μ mol mol（-1）时，突变体的线粒体5-CHO-THF库增加了8倍，并包含了叶片中的大部分5-CHO-THF。相反，10-甲酰基-/5,10-甲基四氢叶酸是在线粒体外形成的。在光呼吸条件下，突变体的叶片甘氨酸水平比野生型高出46倍。此外，当向叶片提供5-CHO-THF时，野生型和突变型叶片都积累了甘氨酸。这些数据表明，5-CHO-THF可以在体内抑制SHMT，从而影响甘氨酸池大小。然而，突变体接近正常的生长表明，即使异常高的5-CHO-THF水平也不会影响通过SHMT或任何其他叶酸依赖反应的通量，即5-CHO-THF在植物中具有良好的耐受性。
Formyltetrahydrofolate (5-CHO-THF) is formed via a second catalytic activity of serine hydroxymethyltransferase (SHMT) and strongly inhibits SHMT and other folate-dependent enzymes in vitro. The only enzyme known to metabolize 5-CHO-THF is 5-CHO-THF cycloligase (5-FCL), which catalyzes its conversion to 5,10-methenyltetrahydrofolate. Because 5-FCL is mitochondrial in plants and mitochondrial SHMT is central to photorespiration, we examined the impact of an insertional mutation in the Arabidopsis 5-FCL gene (At5g13050) under photorespiratory (30 and 370 mu mol of CO2 mol(-1)) and non-photorespiratory (3200 mu mol of CO2 mol(-1)) conditions. The mutation had only mild visible effects at 370 mu mol of CO2 mol(-1), reducing growth rate by similar to 20% and delaying flowering by 1 week. However, the mutation doubled leaf 5-CHO-THF level under all conditions and, under photorespiratory conditions, quadrupled the pool of 10-formyl-/5,10-methenyltetrahydrofolates (which could not be distinguished analytically). At 370 mu mol of CO2 mol(-1), the mitochondrial 5-CHO-THF pool was 8-fold larger in the mutant and contained most of the 5-CHO-THF in the leaf. In contrast, the buildup of 10-formyl-/5,10-methenyltetrahydrofolates was extramitochondrial. In photorespiratory conditions, leaf glycine levels were up to 46-fold higher in the mutant than in the wild type. Furthermore, when leaves were supplied with 5-CHO-THF, glycine accumulated in both wild type and mutant. These data establish that 5-CHO-THF can inhibit SHMT in vivo and thereby influence glycine pool size. However, the near-normal growth of the mutant shows that even exceptionally high 5-CHO-THF levels do not much affect fluxes through SHMT or any other folate-dependent reaction, i.e. that 5-CHO-THF is well tolerated in plants.