Cybulski R L, Fisher R R
Biochemistry. 1976 Jul 27;15(15):3183-7. doi: 10.1021/bi00660a004.
Serine transhydroxymethylase is a latent enzyme of intact rat liver mitochondria. The enzyme is neither solubilized by the selective removal of the outer membrane with digitonin, nor inactivated by concentrations of diazobenzenesulfonate that do not penetrate the inner membrane, but that do inhibit solubilized serine transhydroxymethylase. Swelling of mitochondria was studied in isoosmotic solutions of substrates under conditions that would define transport as neutral uniport, anion-hydroxyl exchange, anion-anion exchange, or electrophoretic. L-Serine and glycine appear to be rapidly taken up by a nonelectrophoretic uniport mechanism, while folate and tetrahydrofolate are not tranported. The results localize the enzyme in the matrix and indicate that the latent activity results from a lack of tetrahydrofolate transport across the inner membrane. Based on these results, the dual localization of serine transhydroxymethylase in the mitochondria and the cytosol is proposed to provide a one-carbon shuttle system to link one-carbon metabolism in the two-cellular compartments.
丝氨酸转羟甲基酶是完整大鼠肝脏线粒体的一种潜在酶。该酶既不会因用洋地黄皂苷选择性去除外膜而溶解，也不会因不穿透内膜但能抑制溶解的丝氨酸转羟甲基酶的重氮苯磺酸盐浓度而失活。在将转运定义为中性单向转运、阴离子 - 羟基交换、阴离子 - 阴离子交换或电泳的条件下，研究了底物等渗溶液中线粒体的肿胀情况。L - 丝氨酸和甘氨酸似乎通过非电泳单向转运机制快速摄取，而叶酸和四氢叶酸则不被转运。结果将该酶定位在基质中，并表明潜在活性是由于四氢叶酸跨内膜转运缺乏所致。基于这些结果，有人提出丝氨酸转羟甲基酶在线粒体和胞质溶胶中的双重定位可提供一个一碳穿梭系统，以连接两个细胞区室中的一碳代谢。
