Kolhouse J F, Stabler S P, Allen R H
Department of Medicine, Biophysics and Genetics, University of Colorado Health Sciences Center, Denver 80262.
Arch Biochem Biophys. 1993 Jun;303(2):355-60. doi: 10.1006/abbi.1993.1295.
Human and mammalian cells contain two cobalamin-dependent enzymes. Methylmalonyl-CoA mutase isomerizes L-methylmalonyl-CoA to succinyl-CoA in the propionyl-CoA pathway while methionine synthase catalyzes the transfer of the methyl group of 5-methyltetrahydrofolate to homocysteine to form methionine. Decreased activity of mutase leads to an increased methylmalonic acid in the serum of humans while decreased activity of methionine synthase leads to increased homocysteine in the serum of humans. In current studies of cultured fibroblasts, methylmalonic acid levels were specifically increased in media of normal fibroblasts exposed to propionate or in fibroblasts with mutations involving mutase. Homocysteine levels were specifically increased in media of normal fibroblasts exposed to reduced folate concentrations or in fibroblasts involving mutations of methionine synthase. In addition, exposure of normal cells to inhibitory cobalamin analogues resulted in an increase of both methylmalonic acid and homocysteine in the media. This method of analysis appears to be both specific and sensitive for reduced activity of these two enzymes in tissue culture.
人类和哺乳动物细胞含有两种钴胺素依赖性酶。甲基丙二酰辅酶A变位酶在丙酰辅酶A途径中将L-甲基丙二酰辅酶A异构化为琥珀酰辅酶A，而甲硫氨酸合酶催化5-甲基四氢叶酸的甲基转移至同型半胱氨酸以形成甲硫氨酸。变位酶活性降低导致人类血清中甲基丙二酸增加，而甲硫氨酸合酶活性降低导致人类血清中同型半胱氨酸增加。在目前对培养的成纤维细胞的研究中，正常成纤维细胞暴露于丙酸盐时或涉及变位酶突变的成纤维细胞的培养基中，甲基丙二酸水平会特异性升高。正常成纤维细胞暴露于低叶酸浓度时或涉及甲硫氨酸合酶突变的成纤维细胞的培养基中，同型半胱氨酸水平会特异性升高。此外，正常细胞暴露于抑制性钴胺素类似物会导致培养基中甲基丙二酸和同型半胱氨酸均增加。这种分析方法似乎对组织培养中这两种酶活性降低具有特异性和敏感性。
