Speck E L, Affronti L F
J Bacteriol. 1969 Mar;97(3):1160-4. doi: 10.1128/jb.97.3.1160-1164.1969.
A strain of Streptococcus faecium (ATCC 8043) which is highly resistant to the antifolic acid compound, amethopterin, was gently ruptured by exposing protoplasts of the organism to a hypotonic solution. The crude lysate resulting there-from was treated by various chemical and physical techniques designed to separate folic acid reductase from dihydrofolic acid reductase. In the process, the enzyme was purified approximately 160-fold; however, throughout the process, the enzyme preparation maintained the ability to reduce folic acid to tetrahydrofolic acid. Attempts to isolate mutants showing a deficiency in either folic acid reductase or dihydrofolic acid reductase were unsuccessful. Based on these results, it is concluded that folic acid is reduced to tetrahydrofolic acid by one enzyme in S. faecium (ATCC 8043). The crude lysate was also subjected to ultracentrifugation. An analysis of the supernatant fluid and the sediment indicated that the reductive activity is located in the soluble fraction of the cell.
一株对抗叶酸化合物氨甲蝶呤高度耐药的粪肠球菌（ATCC 8043），通过将该生物体的原生质体暴露于低渗溶液而被轻柔破碎。由此产生的粗裂解物通过各种化学和物理技术进行处理，旨在将叶酸还原酶与二氢叶酸还原酶分离。在此过程中，该酶被纯化了约160倍；然而，在整个过程中，酶制剂保持了将叶酸还原为四氢叶酸的能力。分离显示叶酸还原酶或二氢叶酸还原酶缺陷的突变体的尝试未成功。基于这些结果，可以得出结论，粪肠球菌（ATCC 8043）中的一种酶将叶酸还原为四氢叶酸。粗裂解物也进行了超速离心。对上清液和沉淀物的分析表明，还原活性位于细胞的可溶部分。
