Lu N C, Hieb W F, Stokstad E L
Proc Soc Exp Biol Med. 1976 Apr;151(4):701-6. doi: 10.3181/00379727-151-39289.
(i) Omission of L-methionine from the medium resulted in an 80% population reduction. Substitution of D,L-homocysteine corrected methionine deficiency in C. briggsae in the presence of supraoptimal vitamin B12 and folic acid. (ii) An absolute vitamin B12 requirement in C. briggsae developed in the medium containing homocysteine at the second subculture. Concentration of 6 ng/ml of vitamin B12 (at 100 ng/ml of folic acid) was sufficient to support maximum growth of C. briggsae in the medium containing homocysteine. (iii) It was found that either supraoptimal folic acid (2000 ng/ml) or supraoptimal vitamin B12 (3750 ng/ml), with homocysteine, supported very little population growth of C. briggsae. However, supraoptimal folic acid and supraoptimal vitamin B12 together supported a maximum population growth. Therefore, it was concluded that both vitamin B12 and folic acid were required for the biosynthesis of methionine from homocysteine. Studies also showed that the two vitamins spared each other for population growth in the medium containing homocysteine.
(i) 培养基中缺少L-甲硫氨酸导致种群数量减少80%。在超最佳水平的维生素B12和叶酸存在的情况下，用D,L-高半胱氨酸替代可纠正秀丽隐杆线虫中的甲硫氨酸缺乏。(ii) 在第二次传代培养时，在含有高半胱氨酸的培养基中，秀丽隐杆线虫产生了对维生素B12的绝对需求。6 ng/ml的维生素B12浓度（在100 ng/ml的叶酸存在下）足以支持秀丽隐杆线虫在含有高半胱氨酸的培养基中实现最大生长。(iii) 研究发现，超最佳水平的叶酸（2000 ng/ml）或超最佳水平的维生素B12（3750 ng/ml）与高半胱氨酸一起，仅支持极少的秀丽隐杆线虫种群生长。然而，超最佳水平的叶酸和超最佳水平的维生素B12共同支持了最大种群生长。因此，得出结论，从高半胱氨酸生物合成甲硫氨酸需要维生素B12和叶酸两者。研究还表明，在含有高半胱氨酸的培养基中，这两种维生素在种群生长方面相互节省。
