Thorndike J, Kisliuk R L, Gaumont Y, Piper J R, Nair M G
Department of Biochemistry, Tufts University, Boston, Massachusetts 02111.
Arch Biochem Biophys. 1990 Mar;277(2):334-41. doi: 10.1016/0003-9861(90)90588-p.
In order to determine the mechanism for the effects of homofolates on growth of Lactobacillus casei, polyglutamated derivatives of homofolate (HPteGlu), dihydrohomofolate and tetrahydrohomofolate (H4HPteGlu) were synthesized and tested as inhibitors of folate-requiring enzymes. The following L. casei enzymes were examined: thymidylate synthase (TS), glycinamide ribonucleotide formyltransferase (GARFT), aminoimidazolecarboxamide ribonucleotide formyltransferase, serine hydroxymethyltransferase and dihydrofolate reductase. Polyglutamates of (6R,S)-H4HPteGlu are potent inhibitors of TS and GARFT. For example, the IC50 values of (6R,S)-H4HPteGlu6 are 0.7 microM for TS and 0.3 microM for GARFT. By contrast, the value for HPteGlu6 is greater than 10 microM for both TS and GARFT. Inhibition of TS and GARFT by (6R,S)-H4HPteGlu derivatives increases with polyglutamate chain length. For TS, the Glu5 and Glu6 derivatives of (6R,S)-H4HPteGlu are 20 and 30 times more potent than the monoglutamate, respectively. For GARFT, the Glu2-6 derivatives are 2-3 times more potent than Glu1. Inhibition of TS and GARFT by (6R,S)-H4HPteGlu polyglutamates is almost entirely due to the unnatural (6R) diastereomer at C-6. Homofolate derivatives are only weak inhibitors of aminoimidazolecarboxamide ribonucleotide formyltransferase, serine hydroxymethyltransferase, and dihydrofolate reductase. We conclude that both TS and GARFT are potential targets of (6R)-H4HPteGlu polyglutamates.
为了确定高叶酸盐对干酪乳杆菌生长影响的机制，合成了高叶酸盐（HPteGlu）、二氢高叶酸盐和四氢高叶酸盐（H4HPteGlu）的多聚谷氨酸化衍生物，并将其作为叶酸依赖性酶的抑制剂进行测试。检测了以下干酪乳杆菌酶：胸苷酸合成酶（TS）、甘氨酰胺核糖核苷酸甲酰基转移酶（GARFT）、氨基咪唑甲酰胺核糖核苷酸甲酰基转移酶、丝氨酸羟甲基转移酶和二氢叶酸还原酶。（6R，S）-H4HPteGlu的多聚谷氨酸是TS和GARFT的有效抑制剂。例如，（6R，S）-H4HPteGlu6对TS的IC50值为0.7微摩尔，对GARFT的IC50值为0.3微摩尔。相比之下，HPteGlu6对TS和GARFT的值均大于10微摩尔。（6R，S）-H4HPteGlu衍生物对TS和GARFT的抑制作用随多聚谷氨酸链长度的增加而增强。对于TS，（6R，S）-H4HPteGlu的Glu5和Glu6衍生物的效力分别比单谷氨酸高20倍和30倍。对于GARFT，Glu2-6衍生物的效力比Glu1高2-3倍。（6R，S）-H4HPteGlu多聚谷氨酸对TS和GARFT的抑制作用几乎完全归因于C-6处的非天然（6R）非对映异构体。高叶酸盐衍生物只是氨基咪唑甲酰胺核糖核苷酸甲酰基转移酶、丝氨酸羟甲基转移酶和二氢叶酸还原酶的弱抑制剂。我们得出结论，TS和GARFT都是（6R）-H4HPteGlu多聚谷氨酸的潜在靶点。
