The biosynthesis of folic acid. XI. Purification and properties of dihydroneopterin aldolase.
The biosynthesis of folic acid. XI. Purification and properties of dihydroneopterin aldolase.
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叶酸的生物合成。
DOI：
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发表时间：
1970
影响因子：
4.8
通讯作者：
G. M. Brown
中科院分区：
文献类型：
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作者：
J. Mathis;G. M. Brown
摘要催化从2-amino-4-hydroxy-6-(d-erythro-1‘，2’，3‘-trihydroxypropyl)-7，8-dihydropteridine(俗称二氢蝶呤)中脱除二碳化合物以产生2-amino-4-hydroxy-6-hydroxymethyl-7，8-dihydropteridine，的酶已从大肠杆菌B的提取物中纯化了约1100倍，形成的两碳化合物经鉴定为乙醇醛。由于该反应类似于醛缩酶催化的反应，因此该酶被命名为二氢蝶呤醛缩酶。该酶具有较高的热稳定性，可以在100℃的高温下耐受5分钟，几乎不会失去活性。该酶的最适pH为9.6。加入EDTA等螯合剂可显著提高该酶的活力。二氢喋呤的Km约为9微米。该酶不能使用以下化合物作为底物来替代二氢喋呤：新喋呤、四氢喋呤、一磷酸二氢喋呤和三磷酸二氢喋呤。该反应的产物2-amino-4-hydroxy-6-hydroxymethyl-7，8-dihydropteridine，是该反应的有效抑制剂。其他二氢蝶呤类药物，包括二氢蝶呤酸和二氢叶酸，是效力较小的抑制剂。结果表明，纯化的二氢喋呤醛缩酶可以利用二氢喋呤的同分异构体2-amino-4-hydroxy-(6-l-threo-trihydroxypropyl)-7，8-dihydropteridine，作为底物，但不能利用相应的d-苏氨酸和L-红血球化合物，而L-红血球化合物可以在纯化的二氢蝶呤醛缩酶和从大肠杆菌提取物中获得的另一种酶的存在下合成2-amino-4-hydroxy-6-hydroxymethyl-7，8-dihydropteridine。这表明，大肠杆菌中含有一种酶，可以催化L-红血球化合物异构化为可被纯化的醛缩酶直接用作底物的化合物(推测为相应的L-苏氨酸化合物)。
Abstract The enzyme that catalyzes the removal of a two-carbon compound from 2-amino-4-hydroxy-6-(d-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydropteridine (known by the trivial name of dihydroneopterin) to yield 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine, has been purified by approximately 1100-fold from extracts of Escherichia coli B. The two-carbon compound formed as a product has been identified as glycolaldehyde. Since the reaction is similar to those reactions catalyzed by aldolases, the enzyme has been named dihydroneopterin aldolase. The enzyme is relatively heat-stable in that it can withstand a temperature of 100° for 5 min with virtually no loss of activity. The enzyme functions optimally at pH 9.6. The addition of chelating agents such as EDTA markedly increases the activity of the enzyme. The Km for dihydroneopterin is approximately 9 µm. The enzyme cannot use the following compounds as substrates in place of dihydroneopterin: neopterin, tetrahydroneopterin, dihydroneopterin monophosphate, and dihydroneopterin triphosphate. The product of the reaction, 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine, is a potent inhibitor of the reaction. Other dihydropteridines, including dihydropteroic acid and dihydrofolic acid, are less potent inhibitors. It was found that purified dihydroneopterin aldolase could use as substrate an epimer of dihydroneopterin, i.e. 2-amino-4-hydroxy-(6-l-threo-trihydroxypropyl)-7,8-dihydropteridine, but the corresponding d-threo and l-erythro compounds could not be utilized, although the l-erythro compound could be utilized for the synthesis of 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine in the presence of purified dihydroneopterin aldolase and another enzyme fraction obtained from extracts of E. coli. This suggests that E. coli contains an enzyme that catalyzes the epimerization of the l-erythro compound to a compound that can be used directly as substrate by the purified aldolase (presumably the corresponding l-threo compound).