Comprehensive Analysis of Cytosolic Nudix Hydrolases in Arabidopsis thaliana

Abstract

Nudix hydrolases are a family of proteins that catalyze the hydrolysis of a variety of nucleoside diphosphate derivatives. Twenty-four genes of the Nudix hydrolase homologues (AtNUDTs) with predicted localizations in the cytosol, chloroplasts, and mitochondria exist in Arabidopsis thaliana. Here, we demonstrated the comprehensive analysis of nine types of cytosolic AtNUDT proteins (AtNUDT1, -2, -4, -5, -6, -7, -9, -10, and -11). The recombinant proteins of AtNUDT2, -6, -7, and -10 showed both ADP-ribose and NADH pyrophosphatase activities with significantly high affinities compared with those of animal and yeast enzymes. The expression of each AtNUDT is individually regulated in different tissues. These findings suggest that most cytosolic AtNUDTs may substantially function in the sanitization of potentially hazardous ADP-ribose and the regulation of the cellular NADH/NAD+ ratio in plant cells. On the other hand, the AtNUDT1 protein had the ability to hydrolyze 8-oxo-dGTP with a Km value of 6.8 μm and completely suppress the increased frequency of spontaneous mutations in the Escherichia coli mutT- strain, indicating that AtNUDT1 is a functional homologue of E. coli MutT in A. thaliana and is involved in the prevention of spontaneous mutation. The results obtained here suggest that the plant Nudix family has evolved in a specific manner that differs from that of yeast and humans. Nudix hydrolases are a family of proteins that catalyze the hydrolysis of a variety of nucleoside diphosphate derivatives. Twenty-four genes of the Nudix hydrolase homologues (AtNUDTs) with predicted localizations in the cytosol, chloroplasts, and mitochondria exist in Arabidopsis thaliana. Here, we demonstrated the comprehensive analysis of nine types of cytosolic AtNUDT proteins (AtNUDT1, -2, -4, -5, -6, -7, -9, -10, and -11). The recombinant proteins of AtNUDT2, -6, -7, and -10 showed both ADP-ribose and NADH pyrophosphatase activities with significantly high affinities compared with those of animal and yeast enzymes. The expression of each AtNUDT is individually regulated in different tissues. These findings suggest that most cytosolic AtNUDTs may substantially function in the sanitization of potentially hazardous ADP-ribose and the regulation of the cellular NADH/NAD+ ratio in plant cells. On the other hand, the AtNUDT1 protein had the ability to hydrolyze 8-oxo-dGTP with a Km value of 6.8 μm and completely suppress the increased frequency of spontaneous mutations in the Escherichia coli mutT- strain, indicating that AtNUDT1 is a functional homologue of E. coli MutT in A. thaliana and is involved in the prevention of spontaneous mutation. The results obtained here suggest that the plant Nudix family has evolved in a specific manner that differs from that of yeast and humans. Nudix 1The abbreviations used are: Nudix, nucleoside diphosphates linked to some moiety X; hMTH1, human MutT. (nucleoside diphosphates linked to some moiety X) hydrolases, which are characterized by a conserved Nudix motif, GX5EX7REVXEEXGU, where U is usually Ile, Leu, or Val (1Bessman M.J. Frick D.N. O'Handley S.F. J. Biol. Chem. 1996; 271: 25059-25062Abstract Full Text Full Text PDF PubMed Scopus (593) Google Scholar), are widely distributed in over 120 species, ranging from viruses to humans (2Xu W. Shen J. Dunn C.A. Desai S. Bessman M.J. Mol. Microbiol. 2001; 39: 286-290Crossref PubMed Scopus (58) Google Scholar). It has been proposed that Nudix hydrolases may be divided into subfamilies based on their major substrates: dinucleoside polyphosphates, ADP-ribose, NADH, nucleotide sugars, or ribo- and deoxynucleoside triphosphates (3Dunn C.A. O'Handley S.F. Frick D.N. Bessman M.J. J. Biol. Chem. 1999; 274: 32318-32324Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar). Because the accumulations of their substrates are often toxic to the cell, their intracellular levels need to be precisely regulated by these enzymes (1Bessman M.J. Frick D.N. O'Handley S.F. J. Biol. Chem. 1996; 271: 25059-25062Abstract Full Text Full Text PDF PubMed Scopus (593) Google Scholar). Among the Nudix hydrolases, Escherichia coli MutT protein hydrolyzes all canonical nucleoside triphosphates with a preference for 8-oxo-dGTP and 8-oxo-GTP, the oxidized form of the free guanine nucleotide, by attacking an active oxygen species, such as a superoxide radical ( O2−˙), H2O2, or a hydroxyl radical (·OH), to the monophosphate form. Because 8-oxo-7,8-dihydroguanine can be incorporated into the nascent strand opposite the adenine and cytosine in the template with almost equal efficiency, resulting in an A:T to C:G transversion mutation (4Tajiri T. Maki H. Sekiguchi M. Mutat. Res. 1995; 336: 257-267Crossref PubMed Scopus (318) Google Scholar, 5Maki H. Sekiguchi M. Nature. 1992; 355: 273-275Crossref PubMed Scopus (792) Google Scholar), MutT functions in the prevention of the misincorporation of such mutagenic nucleotides into DNA or mRNA during DNA replication or transcription (5Maki H. Sekiguchi M. Nature. 1992; 355: 273-275Crossref PubMed Scopus (792) Google Scholar, 6Taddei F. Hayakawa H. Bouton M. Cirinesi A. Matie I. Sekiguchi M. Radman M. Science. 1997; 278: 128-130Crossref PubMed Scopus (250) Google Scholar). In human cells, the accumulation of 8-oxo-7,8-dihydroguanine may be responsible for a significant portion of spontaneous mutations that lead to the induction of cancer, as well as age-related disorders (7Ames B. Shigenaga M. Hagen T. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 7915-7922Crossref PubMed Scopus (5446) Google Scholar). Homologues of E. coli MutT in human (hMTH1) and rodent cells were identified, and they complement the function of MutT in E. coli (8Sakumi K. Furuichi M. Tsuzuki T. Kakuma T. Kawabata S. Maki H. Sekiguchi M. J. Biol. Chem. 1993; 268: 23524-23530Abstract Full Text PDF PubMed Google Scholar, 9Furuichi M. Yoshida M.C. Oda H. Tajiri T. Nakabeppu Y. Tsuzuki T. Sekiguchi M. Genomics. 1994; 24: 485-490Crossref PubMed Scopus (128) Google Scholar, 10Cai J.P. Kakuma T. Tsuzuki T. Sekiguchi M. Carcinogenesis. 1995; 16: 2343-2350Crossref PubMed Scopus (57) Google Scholar, 11Kakuma T. Nishida J. Tsuzuki T. Sekiguchi M. J. Biol. Chem. 1995; 270: 25942-25948Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar). In contrast to human and E. coli, little is known about the functions of Nudix hydrolases and defense systems toward oxidative damage of nucleotides by MutT proteins in higher plants (12Hays J.B. DNA Repair. 2002; 1: 579-600Crossref PubMed Scopus (90) Google Scholar). There are important differences between the life strategies of plants and most eukaryotes. Especially, even under optimal conditions, the photosynthetic electron transport in chloroplasts is inevitably accompanied by the reduction of O2 to O2−˙, which is followed by the production of other active oxygen species such as H2O2 and ·OH, on the reducing side of Photo-system I, although light, as the energy source for photosynthesis, is essential for plant life (13Asada K. Scandalios J.G. Oxidative Stress and the Molecular Biology of Antioxidant Defenses. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1997: 715-735Google Scholar, 14Foyer C.H. Descourvières P. Kunert K.J. Plant Cell Environ. 1994; 17: 507-523Crossref Scopus (1085) Google Scholar). Furthermore, a wide range of environmental stresses, such as drought, high salinity, and low temperature, result in the enhanced production of active oxygen species (14Foyer C.H. Descourvières P. Kunert K.J. Plant Cell Environ. 1994; 17: 507-523Crossref Scopus (1085) Google Scholar, 15Alscher R.G. Donahue J.L. Cramer C.L. Physiol. Plant. 1997; 100: 224-233Crossref Google Scholar, 16Asada K Annu. Rev. Plant Physiol. Plant Mol. Biol. 1999; 50: 601-639Crossref PubMed Scopus (3252) Google Scholar, 17Bowler C Montagu M.V. Inzé D. Annu. Rev. Plant Physiol. Plant Mol. Biol. 1992; 43: 83-116Crossref Scopus (2290) Google Scholar, 18Shigeoka S. Ishikawa T. Tamoi M. Miyagawa Y. Takeda T. Yabuta Y. Yoshimura K. J. Exp. Bot. 2002; 53: 1305-1319Crossref PubMed Google Scholar). Based on a BLAST search (19Altschul S.F. Gish W. Meyers E.W. Lipman D.J. J. Mol. Biol. 1990; 203: 403-410Crossref Scopus (71456) Google Scholar) of the DNA data base, it is likely that 24 open reading frames encoding potential homologues of Nudix hydrolases exist in Arabidopsis thaliana. Among them, AtNUDT1 (At1g68760) was initially characterized as a NADH pyrophosphatase (20Dobrzanska M. Szurmak B. Wyslouch-Cieszynska A. Kraszewska E. J. Biol. Chem. 2002; 277: 50482-50486Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar). In addition, Klaus et al. (21Klaus S.M. Wegkamp A. Sybesma W. Hugenholtz J. Gregory 3rd., J.F. Hanson A.D. J. Biol. Chem. 2005; 280: 5274-5280Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar) recently reported that AtNUDT1 was the closest homologue of Lactococcus lactis YlgG and showed activities toward both dihydroneopterin triphosphate, a precursor of folate, and (deoxy)nucleoside triphosphates, including 8-oxo-dGTP. However, little attention has been given to the effects of MutT-type proteins, including AtNUDT1, on the sanitization system of oxidized nucleotides. Furthermore, several members of the Nudix hydrolase family have recently been described as having either a high specificity for ADP-ribose or including ADP-ribose within their substrate specificity range (3Dunn C.A. O'Handley S.F. Frick D.N. Bessman M.J. J. Biol. Chem. 1999; 274: 32318-32324Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar). Although it is yet to be proven, it is assumed that these enzymes play an important role in maintaining the concentration of intracellular ADP-ribose at a sub-toxic level, because the accumulation of ADP-ribose can be potentially cytotoxic due to its ability to modify protein and to bind to ATP-activated K+ channels (22Kwak Y-G. Park S.-K. Kim U.-H. Han M.-K. Eun J.-S. Cho K.-P. Chae S.-W. Am. J. Physiol. 1996; 271: C464-C468Crossref PubMed Google Scholar). It has been demonstrated that the gene products from Methanococcus jannaschii MJ1149, E. coli orf186, and Saccharomyces cerevisiae YSA1, and the human and mouse Ysa1p homologues, NUDT5 and Nudt5, respectively, have activities toward ADP-ribose (3Dunn C.A. O'Handley S.F. Frick D.N. Bessman M.J. J. Biol. Chem. 1999; 274: 32318-32324Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar, 23Sheikh S. O'Handley S.F. Dunn C.A. Bessman M.J. J. Biol. Chem. 1998; 273: 20924-20928Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar, 24O'Handley S.F. Frick D.N. Dunn C.A. Bessman M.J. J. Biol. Chem. 1998; 273: 3192-3197Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, 25Yang H. Slupska M.M. Wei Y.F. Tai J.H. Luther W.M. Xia Y.R. Shih D.M. Chiang J.H. S. A. J.H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In we characterized the of cytosolic Nudix hydrolases in A. because the is the of their the we demonstrated that AtNUDT1 functions in the defense system of spontaneous the sanitization of oxidized nucleotides. Furthermore, of a of ADP-ribose in A. thaliana suggest that these play in the intracellular concentration of ADP-ribose in plant cells. and Plant thaliana plants were on and in at under at The E. coli strain, and the strain, were from Maki of and The for the was obtained from Nakabeppu The 8-oxo-dGTP was from enzymes and enzymes were from other and enzymes were of and were obtained from of of was from the of plants as described K. Yabuta Y. Tamoi M. Ishikawa T. S. J. 1999; PubMed Scopus Google Scholar). The strand was with an to the The open reading frames of were from the strand the as and The were to the of for the of the nucleotides that the The DNA were into DNA was the with an DNA The resulting were with for AtNUDT1, -2, -4, -5, -6, -7, and for and -10, and for and were into the expression or to The resulting -2, -5, -6, -7, and and -9, -10, and were into E. coli cells. and of AtNUDT coli with -2, -5, -6, -7, or or -9, -10, or was in of of and of an at the were to of the and to an of was to a concentration of and the cells were for at The cells were in and and were with and were at for The recombinant AtNUDT proteins were from the a to the were the of M. PubMed Scopus Google Scholar). and activities of AtNUDT proteins toward to ADP-ribose, and NADH were to the described in and J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar) with some of the μm and of recombinant proteins, was at for The was by of The was with a at a of for the which and The substrates and their products were to their as 8-oxo-dGTP ADP-ribose, NADH, and of the E. coli were with the the specific as and The DNA were with and respectively, and were into The was to the described in et al. (8Sakumi K. Furuichi M. Tsuzuki T. Kakuma T. Kawabata S. Maki H. Sekiguchi M. J. Biol. Chem. 1993; 268: 23524-23530Abstract Full Text PDF PubMed Google Scholar). E. coli or were with or the AtNUDT was in of at The were and of each was in of for toward were by of these on with or the of AtNUDT were from several and of A. thaliana plants of The encoding AtNUDT proteins were with the the and The was used as a was with of for for and for followed by for The products were on of each gene was with the Nudix in A. search for the Nudix hydrolase genes in the for showed that 24 genes encoding the Nudix in A. thaliana. The of the open reading frames of 24 genes are characterized by a of conserved a of the Nudix which as the and nucleotide Among them, AtNUDT1 has been characterized as an NADH, dihydroneopterin triphosphate, and (deoxy)nucleoside (20Dobrzanska M. Szurmak B. Wyslouch-Cieszynska A. Kraszewska E. J. Biol. Chem. 2002; 277: 50482-50486Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar, S.M. Wegkamp A. Sybesma W. Hugenholtz J. Gregory 3rd., J.F. Hanson A.D. J. Biol. Chem. 2005; 280: 5274-5280Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar). The of AtNUDTs showed low with those of E. coli MutT and human and their from to Furthermore, it was predicted that these AtNUDTs were into types by their in the as and Among them, the of is likely a Nudix hydrolase because its predicted an low to those of other and its is higher those of the enzymes in other such as E. coli and In cells, of their substrates are in the J. Biol. Chem. Full Text PDF PubMed Google Scholar), and human is in the cytosolic D. Nishida J. A. Nakabeppu Y. Furuichi M. T. Sekiguchi M. K. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). we on cytosolic types of AtNUDTs (AtNUDT1, -2, and and their and of the AtNUDT encoding cytosolic AtNUDTs were obtained from from of A. thaliana. The open reading of AtNUDT1, -2, and were into or for production of their recombinant proteins with a in E. The recombinant proteins of AtNUDT1, -2, -4, -5, -6, -7, -9, -10, and were with high in the The of each recombinant AtNUDT proteins with their predicted these recombinant proteins were a to as with The production of recombinant proteins of was in the because of the of of AtNUDT the of cytosolic AtNUDTs as Nudix hydrolases, we the activities of these enzymes in the of for triphosphates and types of nucleoside diphosphate with The results are in I. The recombinant proteins of AtNUDT2, -6, -7, and -10 both ADP-ribose and NADH to These proteins showed a high for ADP-ribose compared with the other ADP-ribose H. Slupska M.M. Wei Y.F. Tai J.H. Luther W.M. Xia Y.R. Shih D.M. Chiang J.H. S. A. J.H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), M. jannaschii ADP-ribose S. O'Handley S.F. Dunn C.A. Bessman M.J. J. Biol. Chem. 1998; 273: 20924-20928Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar), and ADP-ribose K. Y. H. PubMed Scopus Google Scholar) The AtNUDT2, -6, and proteins showed a high for of AtNUDT dinucleoside are in an dinucleoside are in an in a of ADP-ribose and NADH in A. M. and et al. et al. et al. et al. et al. et al. H. Slupska M.M. Wei Y.F. Tai J.H. Luther W.M. Xia Y.R. Shih D.M. Chiang J.H. S. A. J.H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google et al. S. O'Handley S.F. Dunn C.A. Bessman M.J. J. Biol. Chem. 1998; 273: 20924-20928Abstract Full Text Full Text PDF PubMed Scopus (51) Google et al. K. Y. H. PubMed Scopus Google et al. J.L. 2001; PubMed Scopus Google et al. J. PubMed Google Scholar). in a AtNUDT1 was reported to have toward NADH in the of (20Dobrzanska M. Szurmak B. Wyslouch-Cieszynska A. Kraszewska E. J. Biol. Chem. 2002; 277: 50482-50486Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar). However, was in the of In addition, AtNUDT1 showed hydrolysis with toward 8-oxo-dGTP to with a high Furthermore, the Km value for 8-oxo-dGTP was that of human K. H. H. Y. Nakabeppu Y. H. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar) and S. cerevisiae T. M. S. Nakabeppu Y. K. Res. PubMed Scopus Google Scholar), and we it the AtNUDT1 protein showed a high for and compared with other MutT-type enzymes of the of in A. thaliana with those of proteins in E. coli, and coli et al. et al. et al. Maki et al. (5Maki H. Sekiguchi M. Nature. 1992; 355: 273-275Crossref PubMed Scopus (792) Google et al. K. H. H. Y. Nakabeppu Y. H. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google et al. T. M. S. Nakabeppu Y. K. Res. PubMed Scopus Google Scholar). in a The protein showed toward mouse human and (2Xu W. Shen J. Dunn C.A. Desai S. Bessman M.J. Mol. Microbiol. 2001; 39: 286-290Crossref PubMed Scopus (58) Google Scholar, J. 2001; PubMed Scopus Google Scholar). to of the substrates was in the -5, and -9, of the characterized Nudix hydrolases the of to we the for of was the most The of in of the compared with the of Klaus et al. (21Klaus S.M. Wegkamp A. Sybesma W. Hugenholtz J. Gregory 3rd., J.F. Hanson A.D. J. Biol. Chem. 2005; 280: 5274-5280Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar) reported that the cytosolic levels of and were and respectively, in The activities toward both 8-oxo-dGTP and other in the of were to be of those in The activities in the of μm were of those in results were in all of the other AtNUDT These results that the essential for is of the E. coli by we the effects of the expression of on the ratio of spontaneous mutation frequency toward in the E. coli mutT- strain, which was of its M. Yoshida M.C. Oda H. Tajiri T. Nakabeppu Y. Tsuzuki T. Sekiguchi M. Genomics. 1994; 24: 485-490Crossref PubMed Scopus (128) Google Scholar). in the mutation frequency of was completely to the as that of the E. coli strain, However, the mutation frequency of cells and were almost the as those of the cells with an These results that the protein has the ability to mutation the sanitization of and as a functional homologue of E. coli MutT in A. of E. coli by the expression of coli with with with with in a of AtNUDT the expression of cytosolic we the levels of cytosolic AtNUDTs in with the in the of all cytosolic AtNUDTs were in and The levels of in the were those in and On the other hand, the levels of and -10 in were those in and These results suggest that the expression of each AtNUDT is individually regulated in different tissues. The Nudix hydrolases are widely distributed in over 120 species ranging from viruses to humans (2Xu W. Shen J. Dunn C.A. Desai S. Bessman M.J. Mol. Microbiol. 2001; 39: 286-290Crossref PubMed Scopus (58) Google Scholar). In A. were types of Nudix hydrolases that were potentially in the cytosol, chloroplasts, and mitochondria In cells, of their are in the J. Biol. Chem. Full Text PDF PubMed Google Scholar), and human is in the cytosolic D. Nishida J. A. Nakabeppu Y. Furuichi M. T. Sekiguchi M. K. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). we here the and of cytosolic Nudix was to that of E. coli MutT and had activities toward 8-oxo-dGTP with a higher those for other substrates and These results suggest that is involved in the prevention of spontaneous mutation. In a E. coli strain, the of spontaneous of A:T to C:G to that of the and F. Hayakawa H. Bouton M. Cirinesi A. Matie I. Sekiguchi M. Radman M. Science. 1997; 278: 128-130Crossref PubMed Scopus (250) Google Scholar). Furthermore, hMTH1, homologues of E. coli MutT in human and rodent cells, can complement the function of MutT in E. coli (8Sakumi K. Furuichi M. Tsuzuki T. Kakuma T. Kawabata S. Maki H. Sekiguchi M. J. Biol. Chem. 1993; 268: 23524-23530Abstract Full Text PDF PubMed Google Scholar, 9Furuichi M. Yoshida M.C. Oda H. Tajiri T. Nakabeppu Y. Tsuzuki T. Sekiguchi M. Genomics. 1994; 24: 485-490Crossref PubMed Scopus (128) Google Scholar, 10Cai J.P. Kakuma T. Tsuzuki T. Sekiguchi M. Carcinogenesis. 1995; 16: 2343-2350Crossref PubMed Scopus (57) Google Scholar, 11Kakuma T. Nishida J. Tsuzuki T. Sekiguchi M. J. Biol. Chem. 1995; 270: 25942-25948Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar). In addition, it has been reported that which has activities toward ADP-ribose, the mutations of the E. coli mutT- T. Hayakawa H. Sekiguchi M. PubMed Scopus Google Scholar). the mutation frequency of the E. coli mutT- to the as that in the E. coli Klaus et al. (21Klaus S.M. Wegkamp A. Sybesma W. Hugenholtz J. Gregory 3rd., J.F. Hanson A.D. J. Biol. Chem. 2005; 280: 5274-5280Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar) have recently that AtNUDT1 is likely to be a that may as a MutT-type Nudix hydrolase and a dihydroneopterin in the result that functions as an in A. thaliana 8-oxo-dGTP that in the nucleotide due to oxidative was in that sanitization of the oxidized nucleotide in the may be in photosynthetic in However, the of the ability of is that of that is higher that of A. thaliana different 8-oxo-7,8-dihydroguanine and by the genes of E. coli and yeast and human for the of 8-oxo-7,8-dihydroguanine from DNA T. K. I. Sekiguchi M. Nakabeppu Y. Mol. 1998; PubMed Scopus Google Scholar, M.V. T. Plant Mol. Biol. 2001; PubMed Scopus (58) Google Scholar). the low ability of AtNUDT1 may be substantially by the functions of and Furthermore, it is likely that some Nudix hydrolases in the chloroplasts and mitochondria may function as a MutT-type to the nucleotide in each On the other hand, AtNUDT2, -6, -7, and -10 had ADP-ribose pyrophosphatase activities with high and Furthermore, the of the ability of these proteins were almost equal to those of and ADP-ribose is during the of protein or or ADP-ribose and is by the of P. Google Scholar). is a of protein in which an ADP-ribose moiety in is to a specific of the protein by in to DNA strand and F. P. S. T. J. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar). The free ADP-ribose is a that of proteins D. Mol. 1994; PubMed Scopus Google Scholar). Furthermore, of the protein by to an cytotoxic J. 1994; PubMed Scopus Google Scholar). about the specific of free ADP-ribose in cellular it to that the of ADP-ribose in the be to the potential of the of free ADP-ribose (1Bessman M.J. Frick D.N. O'Handley S.F. J. Biol. Chem. 1996; 271: 25059-25062Abstract Full Text Full Text PDF PubMed Scopus (593) Google Scholar, 23Sheikh S. O'Handley S.F. Dunn C.A. Bessman M.J. J. Biol. Chem. 1998; 273: 20924-20928Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar). it is likely that the AtNUDTs -6, -7, and that have ADP-ribose pyrophosphatase can play in the free In addition, AtNUDT2, -6, -7, and -10 had NADH pyrophosphatase and It has been reported that NADH pyrophosphatase is involved in the regulation of the cellular NADH/NAD+ an important in maintaining the between the and in the D.N. Bessman M.J. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar), although the of these AtNUDT proteins to the regulation is was at a low in the and were in that the expression of these enzymes with substrate were individually regulated under different had toward although the function of the is yet it was reported that and its are the substrates for Nudix hydrolase in D. (2Xu W. Shen J. Dunn C.A. Desai S. Bessman M.J. Mol. Microbiol. 2001; 39: 286-290Crossref PubMed Scopus (58) Google Scholar), and humans J. 2001; PubMed Scopus Google Scholar). of have the conserved motif, which was to the Nudix was conserved in There was between the conserved and the of the AtNUDT proteins, although the enzymes the Nudix motif, which was Nudix hydrolases in and In addition, AtNUDT2, -6, -7, and -10 showed an as the ADP-ribose these proteins had at the or from the C of the Nudix motif, which is of the of ADP-ribose S. Y. K. S. H. Y. Y. 2002; PubMed Scopus Google Scholar). The results obtained here suggest that the plant Nudix family has evolved in a specific different from that of yeast and are to Maki and of and and Nakabeppu for of the E. coli mutT- and and for and