Hopkins S, Schirch V
J Biol Chem. 1984 May 10;259(9):5618-22.
The enzyme 5,10-methenyltetrahydrofolate synthetase has been purified to homogeneity from rabbit liver. The substrates are MgATP and 5-formyltetrahydrofolate. The enzyme will accept as substrates a variety of divalent metal ions and trinucleotides. The products of the reaction are 5,10-methenyltetrahydrofolate, ADP, and inorganic phosphate. The enzyme is a monomeric protein with a molecular weight of about 28,000. The stability of the enzyme is unusually sensitive to pH and ionic strength. Initial velocity studies suggest that the enzyme catalyzes a sequential mechanism. The turnover number of the enzyme is 300/min at 30 degrees C. The Km values for MgATP and 5-formyltetrahydrofolate are 0.3 mM and 0.5 microM, respectively. Product and dead-end inhibition studies indicate that substrates bind to the enzyme by a random mechanism. Vmax and the Km for MgATP are essentially constant over the pH range of 5.0-7.5. The results suggest that the enzyme catalyzes a reaction which serves as a salvage pathway to generate metabolically active one-carbon units from 5-formyltetrahydrofolate.
已从兔肝中纯化出5,10-亚甲基四氢叶酸合成酶至均一状态。底物是MgATP和5-甲酰四氢叶酸。该酶可接受多种二价金属离子和三核苷酸作为底物。反应产物是5,10-亚甲基四氢叶酸、ADP和无机磷酸。该酶是一种分子量约为28,000的单体蛋白。酶的稳定性对pH和离子强度异常敏感。初始速度研究表明该酶催化一种顺序机制。在30℃时该酶的转换数为300/分钟。MgATP和5-甲酰四氢叶酸的Km值分别为0.3 mM和0.5 μM。产物和终产物抑制研究表明底物通过随机机制与酶结合。在5.0 - 7.5的pH范围内，Vmax和MgATP的Km基本恒定。结果表明该酶催化的反应是一条补救途径，可从5-甲酰四氢叶酸生成代谢活性的一碳单位。
