Kumar P M, North J A, Mangum J H, Rao N A
Proc Natl Acad Sci U S A. 1976 Jun;73(6):1950-3. doi: 10.1073/pnas.73.6.1950.
Serine transhydroxymethylase (5,10-methylenetetrahydrofolate: glycine hydroxymethyl transferase, EC 2.1.2.1) purified 200-fold from pig kidneys showed cooperative interactions with tetrahydrofolate with a Hill coefficient (n value) of 3.9 and a substrate concentration at 50% of maximum velocity, the S(0.5) value, of 0.5 mM. The enzyme in mouse liver and kidney homogenates also showed cooperative interactions with tetrahydrofolate. However, the enzyme obtained from L1210 solid tumors of mice, and from livers and kidneys of mice inoculated with L1210 cells exhibited hyperbolic saturation kinetics and gave a Michaelis constant, Km, value of 0.5 mM for tetrahydrofolate. The interaction of serine with the enzyme from pig kidney, from tissues of normal or tumor-bearing mice, or from L1210 tumors was hyperbolic with a Km of 0.9 mM. The specific activities of the enzyme in the L1210 tumor and in mouse liver were 10-fold higher than in pig or mouse kidney. There was no significant change in the levels of the enzyme in mouse liver and kidney on inoculation with L1210 cells. These results suggest that a tumor can bring about biochemical changes in tissues that are distal to the tumor.
从猪肾中纯化200倍的丝氨酸转羟甲基酶（5,10-亚甲基四氢叶酸：甘氨酸羟甲基转移酶，EC 2.1.2.1）与四氢叶酸呈现协同相互作用，希尔系数（n值）为3.9，底物浓度为最大速度的50%时，即S(0.5)值为0.5 mM。小鼠肝脏和肾脏匀浆中的该酶也与四氢叶酸呈现协同相互作用。然而，从小鼠的L1210实体瘤以及接种L1210细胞的小鼠的肝脏和肾脏中获得的该酶表现出双曲线饱和动力学，四氢叶酸的米氏常数Km值为0.5 mM。丝氨酸与来自猪肾、正常或荷瘤小鼠组织或L1210肿瘤的酶的相互作用呈双曲线，Km为0.9 mM。L1210肿瘤和小鼠肝脏中该酶的比活性比猪或小鼠肾脏中的高10倍。接种L1210细胞后，小鼠肝脏和肾脏中该酶的水平没有显著变化。这些结果表明，肿瘤可导致肿瘤远端组织发生生化变化。
