Johlin F C, Swain E, Smith C, Tephly T R
Department of Internal Medicine, University of Iowa, Iowa City 52242.
Mol Pharmacol. 1989 Jun;35(6):745-50.
Methanol poisoning in primates and humans is due to formate accumulation as a result of low rates of formate oxidation. This toxicity is not seen in rats, where formate oxidation rates are high. Formate oxidation in vivo is dependent on hepatic tetrahydrofolate levels and on the activity of the enzyme 10-formyl-tetrahydrofolate (10-formyl-H4folate) dehydrogenase (EC 1.5.1.6). Because hepatic 10-formyl-H4folate dehydrogenase activity is lower in human liver than in rat liver, studies were performed investigating the properties of this enzyme in rat and human liver. 10-Formyl-H4folate dehydrogenase was purified to homogeneity from rat and human liver and was found to possess similar subunit molecular weights on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (96,000). N-Terminal amino acid analysis of the pure proteins showed an identical sequence for the first 16 amino acids. Antibodies raised in rabbits against the rat liver enzyme were inhibitory toward the activity of both rat and human liver enzymes and appeared to recognize only the 10-formyl-H4folate dehydrogenase in cytosolic preparations of rat and human liver. Immunoblots of pure rat and human liver 10-formyl-H4folate dehydrogenase showed similar staining intensity. It is concluded that rat and human liver 10-formyl-H4folate dehydrogenase possess very similar properties and that the activity of the enzyme in human liver is lower than that of rat liver, due to a reduced amount of enzyme protein in human liver. This may be an important factor in regulating formate oxidation in humans and may explain, in part, the accumulation of formate and the mechanism of toxicity of methanol in humans.
灵长类动物和人类的甲醇中毒是由于甲酸氧化速率低导致甲酸积累所致。在大鼠中未观察到这种毒性，因为大鼠的甲酸氧化速率很高。体内甲酸氧化取决于肝脏四氢叶酸水平和10-甲酰四氢叶酸（10-formyl-H4folate）脱氢酶（EC 1.5.1.6）的活性。由于人类肝脏中10-甲酰-H4叶酸脱氢酶的活性低于大鼠肝脏，因此进行了研究以调查该酶在大鼠和人类肝脏中的特性。从大鼠和人类肝脏中纯化出均一的10-甲酰-H4叶酸脱氢酶，在十二烷基硫酸钠-聚丙烯酰胺凝胶电泳上发现其具有相似的亚基分子量（96,000）。对纯蛋白进行N端氨基酸分析，结果显示前16个氨基酸的序列相同。用兔抗大鼠肝脏酶产生的抗体对大鼠和人类肝脏酶的活性均有抑制作用，并且似乎仅识别大鼠和人类肝脏胞质制剂中的10-甲酰-H4叶酸脱氢酶。纯大鼠和人类肝脏10-甲酰-H4叶酸脱氢酶的免疫印迹显示出相似的染色强度。结论是，大鼠和人类肝脏的10-甲酰-H4叶酸脱氢酶具有非常相似的特性，并且人类肝脏中该酶的活性低于大鼠肝脏，这是由于人类肝脏中酶蛋白的量减少所致。这可能是调节人类甲酸氧化的一个重要因素，并且可能部分解释了甲酸的积累以及人类甲醇中毒的机制。
