Vitamin B9 (folate) biosynthesis pathway

Tetrahydrofolate (THF) acts as a carrier for one-carbon units and, less often, as an electron donor. THF contains pterin, p-aminobenzoate, and glutamate moieties. The pterin is made in the cytosol from GTP, p-aminobenzoate is made from chorismate in plastids, and the two are coupled together in mitochondria to give dihydropteroate. Glutamylation and reduction steps in mitochondria then yield THF (Hanson and Gregory, 2011; Ravanel et al., 2011). THF and its one-carbon derivatives (collectively termed folates) occur mainly as polyglutamates; these have a short polyglutamyl tail that can be added in mitochondria, plastids, or cytosol. Folate polyglutamates can be imported into vacuoles, where the polyglutamyl tail can be removed by γ-glutamylhydrolase. p-Aminobenzoate can be converted to its glucose ester in the cytosol, and imported into vacuoles.

四氢叶酸（THF）充当一碳单位的载体，偶尔也作为电子供体。THF包含蝶呤、对氨基苯甲酸和谷氨酸基团。蝶呤在细胞质中由GTP合成，对氨基苯甲酸在质体中由香豆酸合成，两者在细胞器中耦合，生成二氢蝶呤。随后，线粒体内的谷氨酰化和还原步骤产生THF（Hanson and Gregory, 2011；Ravanel et al., 2011）。THF及其一碳衍生物（统称为叶酸）主要以多谷氨酸形式存在；这些叶酸具有短的多谷氨酰基尾，该尾可在线粒体、质体或细胞质中添加。叶酸多谷氨酸可以被导入液泡中，在那里多谷氨酰基尾可以被γ-谷氨酰水解酶移除。对氨基苯甲酸可以在细胞质中转化为葡萄糖酯，并导入液泡。