Mouse folylpoly-γ-glutamate synthetase isoforms respond differently to feedback inhibition by folylpolyglutamate cofactors
Mouse folylpoly-γ-glutamate synthetase isoforms respond differently to feedback inhibition by folylpolyglutamate cofactors
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DOI：
10.1021/bi015644d
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发表时间：
2002-01-08
期刊：
影响因子：
2.9
通讯作者：
Moran, RG
中科院分区：
文献类型：
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作者：
Andreassi, JL;Moran, RG
叶酸聚-γ-谷氨酸合成酶（FPGS）是负责在细胞中代谢捕获用于核苷酸和氨基酸生物合成的还原叶酸辅因子的酶。在小鼠组织中表达的FPGS有两种亚型，一种在分化的组织中表达，主要是肝和肾，另一种在所有快速增殖的细胞类型中表达。本研究旨在寻找功能差异，以解释两种小鼠FPGS物种的进化。重组胞质小鼠同工酶进行了比较，相对于稳态动力学，形成的聚谷氨酸衍生物的链长，和主要减少folylpentaglutamate辅因子的终产物抑制。两种异构体在催化添加1摩尔谷氨酸至还原叶酸单谷氨酸底物中同样有效。每种同种型也能够形成模型叶酸的长链聚谷氨酸衍生物，5，10-二脱氮四氢叶酸。相比之下，与分化组织中表达的同种型相比，源自快速增殖组织的FPGS同种型对（6 R）-5，10-CH 2-H（4）PteGlu（5）和（6S）-H（4）PteGlu（5）的抑制更敏感，抑制常数（Ki）分别低13倍和6倍。有趣的是，每种同工酶对（6 R）-10-CHO-H（4）PteGlu（5）的抑制作用同样敏感。我们得出的结论是，小鼠肝脏和肾脏中表达的FPGS对5，10-CH 2-H（4）PteGlu（5-6）和H（4）PteGlu（5-6）反馈抑制的敏感性降低，可能已经演变为比快速增殖组织中发现的更大的叶酸辅因子池的pen-nit积累。
Folylpoly-gamma-glutamate synthetase (FPGS) is the enzyme responsible for metabolic trapping of reduced folate cofactors in cells for use in nucleotide and amino acid biosynthesis. There are two isoforms of FPGS expressed in mouse tissues, one is expressed in differentiated tissue, principally liver and kidney, and the other in all rapidly proliferating cell types. The present study sought the functional difference that would explain the evolution of two mouse FPGS species. Recombinant cytosolic mouse isozymes were compared with respect to steady state kinetics, chain length of polyglutamate derivatives formed, and end-product inhibition by the major reduced folylpentaglutamate cofactors. Both isoforms were equally effective in catalyzing the addition of a mole of glutamic acid to reduced folate monoglutamate substrates. Each isoform was also capable of forming long chain polyglutamate derivatives of the model folate, 5,10-dideazatetrahydrofolate. In contrast, the FPGS isoform derived from rapidly proliferating tissue was much more sensitive to inhibition by (6R)-5,10-CH2-H(4)PteGlu(5) and (6S)-H(4)PteGlu(5) than the isoform expressed in differentiated tissues, as demonstrated by 13- and 6-fold lower inhibition constants (K-i), respectively. Interestingly, each isozyme was equally sensitive to inhibition by (6R)-10-CHO-H(4)PteGlu(5). We drew the conclusion that the decreased sensitivity of the FPGS expressed in mouse liver and kidney to feedback inhibition by 5,10-CH2-H(4)PteGlu(5-6) and H(4)PteGlu(5-6) may have evolved to pen-nit accumulation of a larger folate cofactor pool than that found within rapidly proliferating tissue.