Mouse Folylpoly--glutamate Synthetase Isoforms Respond Differently to Feedback Inhibition by Folylpolyglutamate Cofactors
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- 作者：John L. Andreassi II and Richard G. Moran
- 刊名：Biochemistry
- 出版年：2002
- 出版时间：January 8, 2002
- 年：2002
- 卷：41
- 期：1
- 页码：226 - 235
- 全文大小：125K
- 年卷期：v.41,no.1(January 8, 2002)
- ISSN：1520-4995
文摘
Folylpoly-
-glutamate synthetase (FPGS) is the enzyme responsible for metabolic trapping ofreduced folate cofactors in cells for use in nucleotide and amino acid biosynthesis. There are two isoformsof 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 thatwould explain the evolution of two mouse FPGS species. Recombinant cytosolic mouse isozymes werecompared with respect to steady state kinetics, chain length of polyglutamate derivatives formed, andend-product inhibition by the major reduced folylpentaglutamate cofactors. Both isoforms were equallyeffective 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 wasmuch more sensitive to inhibition by (6R)-5,10-CH2-H4PteGlu5 and (6S)-H4PteGlu5 than the isoformexpressed in differentiated tissues, as demonstrated by 13- and 6-fold lower inhibition constants (Ki),respectively. Interestingly, each isozyme was equally sensitive to inhibition by (6R)-10-CHO-H4PteGlu5.We drew the conclusion that the decreased sensitivity of the FPGS expressed in mouse liver and kidneyto feedback inhibition by 5,10-CH2-H4PteGlu5-6 and H4PteGlu5-6 may have evolved to permit accumulationof a larger folate cofactor pool than that found within rapidly proliferating tissue.
-glutamate synthetase (FPGS) is the enzyme responsible for metabolic trapping ofreduced folate cofactors in cells for use in nucleotide and amino acid biosynthesis. There are two isoformsof 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 thatwould explain the evolution of two mouse FPGS species. Recombinant cytosolic mouse isozymes werecompared with respect to steady state kinetics, chain length of polyglutamate derivatives formed, andend-product inhibition by the major reduced folylpentaglutamate cofactors. Both isoforms were equallyeffective 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 wasmuch more sensitive to inhibition by (6R)-5,10-CH2-H4PteGlu5 and (6S)-H4PteGlu5 than the isoformexpressed in differentiated tissues, as demonstrated by 13- and 6-fold lower inhibition constants (Ki),respectively. Interestingly, each isozyme was equally sensitive to inhibition by (6R)-10-CHO-H4PteGlu5.We drew the conclusion that the decreased sensitivity of the FPGS expressed in mouse liver and kidneyto feedback inhibition by 5,10-CH2-H4PteGlu5-6 and H4PteGlu5-6 may have evolved to permit accumulationof a larger folate cofactor pool than that found within rapidly proliferating tissue.