White R H
Department of Biochemistry and Nutrition, Virginia Polytechnic Institute and State University, Blacksburg 24061.
Biochemistry. 1990 Jun 5;29(22):5397-404. doi: 10.1021/bi00474a027.
The biosynthetic pathway for the generation of the methylated pterin in methanopterins was determined for the methanogenic bacteria Methanococcus volta and Methanobacterium formicicum. Extracts of M. volta were found to readily cleave L-7,8-dihydroneopterin to 7,8-dihydro-6-(hydroxymethyl)pterin, which was confirmed to be a precursor of the pterin portion of the methanopterin. [methylene-2H]-6-(Hydroxymethyl)pterin was incorporated into methanopterin by growing cells of M. volta to an extent of 30%. Both the C-11 and C-12 methyl groups of methanopterin originate from [methyl-2H3]methionine, as confirmed by the incorporation of two C2H3 groups into 6-ethyl-7-methylpterin, a pterin-containing fragment derived from methanopterin. Cells grown in the presence of [methylene-2H]-6-(hydroxymethyl)pterin, [ethyl-2H4]-6-[1 (RS)-hydroxyethyl]pterin, [methyl-2H3]-6- (hydroxymethyl)-7-methylpterin, [ethyl-2H4, methyl-2H3]-6-[1 (RS)-hydroxyethyl]-7-methylpterin, and [1-ethyl-3H]-6-[1 (RS)-hydroxyethyl]-7-methylpterin showed that only the non-7-methylated pterins were incorporated into methanopterin. Cells extracts of M. formicicum readily condensed synthetic [methylene-3H]-7,8-H2-6-(hydroxymethyl)pterin-PP with methaniline to generate demethylated methanopterin, which is then methylated to methanopterin by the cell extract in the presence of S-adenosylmethionine. These observations indicate that the pterin portion of methanopterin is biosynthetically derived from 7,8-H2-6-(hydroxymethyl)pterin, which is coupled to methaniline by a pathway analogous to the biosynthesis of folic acid. This pathway for the biosynthesis of methanopterin represents the first example of the modification of the specificity of a coenzyme through a methylation reaction.
针对产甲烷细菌沃氏甲烷球菌（Methanococcus volta）和甲酸甲烷杆菌（Methanobacterium formicicum），确定了产甲烷蝶呤中甲基化蝶呤的生物合成途径。研究发现，沃氏甲烷球菌的提取物能够轻易地将L-7,8-二氢新蝶呤裂解为7,8-二氢-6-（羟甲基）蝶呤，已证实其为产甲烷蝶呤中蝶呤部分的前体。[亚甲基-2H]-6-（羟甲基）蝶呤被沃氏甲烷球菌的生长细胞整合到产甲烷蝶呤中的比例为30%。产甲烷蝶呤的C-11和C-12甲基均源自[甲基-2H3]甲硫氨酸，这一点通过两个C2H3基团整合到6-乙基-7-甲基蝶呤（一种源自产甲烷蝶呤的含蝶呤片段）得以证实。在[亚甲基-2H]-6-（羟甲基）蝶呤、[乙基-2H4]-6-[1（RS）-羟乙基]蝶呤、[甲基-2H3]-6-（羟甲基）-7-甲基蝶呤、[乙基-2H4，甲基-2H3]-6-[1（RS）-羟乙基]-7-甲基蝶呤以及[1-乙基-3H]-6-[1（RS）-羟乙基]-7-甲基蝶呤存在的条件下生长的细胞表明，只有未甲基化的蝶呤被整合到产甲烷蝶呤中。甲酸甲烷杆菌的细胞提取物能够轻易地将合成的[亚甲基-3H]-7,8-H2-6-（羟甲基）蝶呤-PP与甲胺缩合生成去甲基产甲烷蝶呤，然后在细胞提取物存在S-腺苷甲硫氨酸的情况下将其甲基化为产甲烷蝶呤。这些观察结果表明产甲烷蝶呤的蝶呤部分在生物合成上源自7,8-H2-6-（羟甲基）蝶呤，其通过与叶酸生物合成类似的途径与甲胺偶联。这种产甲烷蝶呤的生物合成途径代表了通过甲基化反应改变辅酶特异性的首个实例。
