401
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Averett DR, Lubbers C, Elion GB, Spector T. Ribonucleotide reductase induced by herpes simplex type 1 virus. Characterization of a distinct enzyme. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(17)44573-x] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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402
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Spector T, Jones TE. Guanosine 5'-monophosphate reductase from Leishmania donovani. A possible chemotherapeutic target. Biochem Pharmacol 1982; 31:3891-7. [PMID: 7159467 DOI: 10.1016/0006-2952(82)90307-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
GMP reductase was highly purified from promastigotes of Leishmania donovani by chromatography on a single DEAE-cellulose column. Bimodal substrate saturation curves resulted in a 1/v versus 1/[GMP] plot that curved downward above 40 microM GMP. The kinetic constants were, therefore, obtained with GMP below this concentration. The K'm for GMP was 21 microM at pH 6.9. The enzyme was very sensitive to activation by GTP. At 20 microM GMP, a maximum of 600% activation occurred at 100 microM GTP. Half-maximal activation occurred at 8 microM GTP. GTP at 100 microM did not affect the K'm for GMP but did increase its V'max by 7-fold. Xanthosine monophosphate (XMP) and IMP analogs served equally well as competitive inhibitors versus GMP. The inhibition by the analogs and the activation by GTP were mutually antagonistic processes. The inhibition by the IMP analogs, allopurinol nucleotide and thiopurinol nucleotide is of chemotherapeutic interest because these compounds were shown previously to be produced in Leishmania from the anti-leishmanial agents allopurinol and thiopurinol. These nucleotides were 100- and 20-fold, respectively, more potent inhibitors of GMP reductase from L. donovani than of the corresponding enzyme from human erythrocytes.
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403
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Nelson DJ, Lafon SW, Jones TE, Spector T, Berens RL, Marr JJ. The metabolism of formycin B in Leishmania donovani. Biochem Biophys Res Commun 1982; 108:349-54. [PMID: 7150292 DOI: 10.1016/0006-291x(82)91873-3] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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404
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Marr JJ, Berens RL, Nelson DJ, Krenitsky TA, Spector T, LaFon SW, Elion GB. Antileishmanial action of 4-thiopyrazolo (3.4-d) pyrimidine and its ribonucleoside. Biological effects and metabolism. Biochem Pharmacol 1982; 31:143-8. [PMID: 7073876 DOI: 10.1016/0006-2952(82)90203-9] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Thiopurinol [4-thiopyrazolo(3.4-dyprimidine, TPP] and its ribonucleoside (TPPR) were effective in vitro against the intracellular and extracellular forms of L. braziliensis and L. mexicana. They also inhibited the transformation of the amastigote of L. donovani to the promastigote. These thio-analogues had about the same activity as allopurinol [4-hydroxypyrazolo(3.4-d)pyrimidine, HPP] and its ribonucleoside (HPPR). the thiopyrazolopyrimidines were converted primarily to the ribonucleoside-5' -phosphate (TPPR-MP) and to an unidentified metabolite, but not to any of the adenine ribonucleoside analogues previously shown to be formed from allopurinol and its ribonucleoside. There was an antagonism between the growth-inhibitory effects of allopurinol and thiopurinol. This is consistent with the findings that the intracellular concentrations of TPP and TPPR-MP are sufficient to inhibit the conversion of allopurinol to allopurinol ribonucleotide (HPPR-MP) by the hypoxanthine-guanine phosphoribosyltransferase by 30 per cent and the amination of HPPR-MP by adenylosuccinate synthetase by 50 per cent respectively. Consequently, the incorporation of the aminated product (aminopyrazolopyrimidine) into RNA was substantially decreased. The difference in metabolism between the thio- and hydroxypyrazolopyrimidines suggests a difference in their mechanisms of action against the pathogenic leishmania.
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405
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Spector T, Berens RL, Marr JJ. Adenylosuccinate synthetase and adenylosuccinate lyase from Trypanosoma cruzi, Specificity studies with potential chemotherapeutic agents. Biochem Pharmacol 1982; 31:225-9. [PMID: 7037007 DOI: 10.1016/0006-2952(82)90215-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Adenylosuccinate (succino-AMP) synthetase and succino-AMP lyase isolated from epimastigotes of Trypanosoma cruzi by chromatography on phosphocellulose. The synthetase was capable of catalyzing the condensation of aspartic acid with IMP and several IMP analogs. The reaction with allopurinol ribonucleotide is of potential chemotherapeutic interest. This analog was slowly converted to its corresponding succino-AMP analog with a Km' of 140 micrometers (cf. IMP at 10 micrometers) and a Vmax' of 0.3 per cent the rate with IMP. The comparable reaction with this analog does not occur with succino-AMP synthetase from a representative mammalian source [T. Spector and R. L. Miller, Biochim. biophys. Acta 455, 509 (1976)]. The protozoal succino-AMP lyase had a broad substrate which was characteristic of this enzyme from many sources. It catalyzed the rapid and efficient cleavage of all the succino-AMP analogs that were produced by succino-AMP synthetase. Thus, these two enzymes appear to be responsible for the selective amination of allopurinol ribonucleotide in T. cruzi. The metabolically produced AMP analog may be the agent or a precursor of the agent that accounts for the anti-growth activity of allopurinol in these organisms. Similar selective amination was observed previously with these enzymes from Leishmania donovani [T. Spector, T. E. Jones and G. B. Elion, J. biol. Chem. 254, 8422 (1979)]. Thiopurinol ribonucleotide was not a substrate of succino-AMP synthetase from T. cruzi, but it was an inhibitor with a K1 = 33 micrometers. Therefore, the weakness of thiopurinol's anti-growth activity with T. cruzi is not due to its inability to inhibit this enzyme.
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406
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407
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Spector T, Hajian G. Statistical methods to distinguish competitive, noncompetitive, and uncompetitive enzyme inhibitors. Anal Biochem 1981; 115:403-9. [PMID: 7304967 DOI: 10.1016/0003-2697(81)90025-7] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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408
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409
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410
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Spector T, Jones TE, Elion GB. Specificity of adenylosuccinate synthetase and adenylosuccinate lyase from Leishmania donovani. Selective amination of an antiprotozoal agent. J Biol Chem 1979; 254:8422-6. [PMID: 468834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
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411
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Spector T, Jones TE, Miller RL. Reaction mechanism and specificity of human GMP reductase. Substrates, inhibitors, activators, and inactivators. J Biol Chem 1979; 254:2308-15. [PMID: 218932] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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412
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Spector T. Precise temperature control of the Gilford spectrophotometer: a simple and inexpensive modification. Anal Biochem 1979; 93:171-3. [PMID: 434460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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413
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Spector T. Refinement of the coomassie blue method of protein quantitation. A simple and linear spectrophotometric assay for less than or equal to 0.5 to 50 microgram of protein. Anal Biochem 1978; 86:142-6. [PMID: 655375 DOI: 10.1016/0003-2697(78)90327-5] [Citation(s) in RCA: 1330] [Impact Index Per Article: 28.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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414
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415
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Miller RL, Adamczyk DL, Spector T. Reassessment of the interactions of guanylate kinase and 6-thioguanosine 5'-phosphate. Biochem Pharmacol 1977; 26:1573-6. [PMID: 197968 DOI: 10.1016/0006-2952(77)90071-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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416
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Spector T. Mammalian adenylosuccinate lyase. Participation in the conversion of 2'-dIMP and beta-D-arabinosyl-IMP to adenine nucleotides. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 481:741-5. [PMID: 300632 DOI: 10.1016/0005-2744(77)90308-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Adenylosuccinate synthetase (EC 6.3.4.4) from rabbit muscle efficiently catalyzes the formation of 2'-deoxyadenylosuccinate and beta-D-arabinosylade-nylosuccinate from 2'-dIMP and beta-D-arabinosylIMP (Spector, T. and Miller, RL. (1976) Biochim. Biophys. Acta 445, 509-517). These novel analogs of adenylosuccinate were synthesized with this enzyme and their kinetic constants were determined with adenylosuccinate lyase purified from Ehrlich ascites cells. 2'-Deoxyadenylosuccinate and beta-D-arabinosyladenylosuccinate were readily cleaved to 2'-dAMP and beta-D-arabinosylAMP, respectively. Their Km values were similar to that of adenylosuccinate (3-6 micronM) and their substrate efficiencies (V/Km) were 120 for 2-deoxyadenylosuccinate and 32 for beta-D-arabinosyl-adenylosuccinate, compared to a value of 100 for adenylosuccinate. The products of the reactions, 2'-dAMP and beta-D-arabinosylAMP, were competitive inhibitors with Ki values of 5 and 87 micronM, respectively. ATP and ADP were considerably weaker competitive inhibitors with Ki values of 200-300 micronM. IMP, GMP, xanthosine 5'-monophosphate, 6-thioIMP and 6-thioGMP had Ki values greater than 200 micronM.
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417
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418
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Agarwal RP, Spector T, Parks RE. Tight-binding inhibitors--IV. Inhibition of adenosine deaminases by various inhibitors. Biochem Pharmacol 1977; 26:359-67. [PMID: 849330 DOI: 10.1016/0006-2952(77)90192-7] [Citation(s) in RCA: 307] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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419
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Spector T, Jones TE, Krenitsky TA, Harvey RJ. Guanosine monophosphate synthetase from Ehrlich ascites cells. Multiple inhibition by pyrophosphate and nucleosides. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 452:597-607. [PMID: 188467 DOI: 10.1016/0005-2744(76)90210-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
GMP synthetase (xanthosine-5'-phosphate: ammonia ligase (AMP-forming), EC 6.3.4.1) from Ehrlich ascites cells was found to be subject to multiple inhibition by its reaction product, PPi, and some analogs of adenosine. PPi and the nucleoside (N) inhibitors were also capable of individually inhibiting this enzyme. Under no conditions did the inhibition appear to be irreversible or "pseudoinactivating" in nature. The individual inhibition by PPi was competitive with respect to ATP (KI = 0.42 mM). Conversely, in the absence of PPi, the binding of N was noncompetitive with ATP, but shifted to a competitive pattern when PPi was present. Furthermore, with the inhibitors in concert, there was an apparent lowering of the KI values for both inhibitors. This data was consistent with either PPi functioning to tighten the binding of N at a noncatalytic site (positive cooperativity) or with PPi actually opening a second binding site for N in addition to the non-catalytic site. Although this study did not distinguish which of these events was occurring, it did reveal that the intensity of the effect of PPi appeared to be constant. That is, for various N inhibitors with a range of independently determined KI values from 26 to 1650 muM, the ratio of their KI values determined in the absence of PPi to the values determined in the presence of PPi was always 38 +/- 1.
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420
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Spector T, Miller RL. Mammalian adenylosuccinate synthetase. Nucleotide monophosphate substrates and inhibitors. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 445:509-17. [PMID: 953040 DOI: 10.1016/0005-2744(76)90104-2] [Citation(s) in RCA: 45] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Guanylate cyclase (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2) activity was examined in preparations from normal rat liver and a series of Morris hepatomas...
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421
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Spector T. Studies with GMP synthetase from Ehrlich ascites cells. Purification, properties, and interactions with nucleotide analogs. J Biol Chem 1975; 250:7372-6. [PMID: 240826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
GMP synthetase has been purified 57-fold from Ehrlich ascites cells. The enzyme was found to be stable and to have an approximate molecular weight of 85,000 (determined by gel filtration). Its activity was stimulated by dithiothreitol and inhibited by 2-mercaptoethanol, p-chloromercuribenzoate, and hydroxylamine. Both ammonia and glutamine could serve as amino group donors. While none of the 10 triphosphate purine and pyrimidine nucleotides studied were able to substitute for ATP as the energy donor for the reaction, all of these compounds were able to bind to the ATP site. The Ki values for CTP, beta-D-arabinofuranosyl-ATP, and 1-N6-ethenoATP were slightly lower than the Km of ATP (0.28 mM). Six monophosphate nucleotides were aminated by this enzyme. Listed in order of their substrate efficiency (Vmax/Km), they are: xanthosine 5'-phosphate(XMP) (28,000); 2'-dXMP (1,200); 8-azaXMP (320); 6-thioXMP (200); beta-D-arabinofuranosyl-XMP (72); 1-ribosyloxipurinol 5'-phosphate (0.5). 6-ThioXMP was a strong alternative substrate inhibitor with a Ki of 5 muM. The aminated products of the reaction (four studied) were competitive inhibitors with respect to XMP.
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422
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Spector T. Studies with GMP synthetase from Ehrlich ascites cells. Purification, properties, and interactions with nucleotide analogs. J Biol Chem 1975. [DOI: 10.1016/s0021-9258(19)40954-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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423
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Spector T, Beacham LM. Guanosine monophosphate synthetase from Escherichia coli B-96. Inhibition by nucleosides. J Biol Chem 1975; 250:3101-7. [PMID: 164459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mechanism of inhibition of GMP synthetase by purine and purine-analog nucleosides was investigated. It was found that in addition to allowing the nucleoside to bind to the enzyme (Udaka, S., and Moyed, H. S. (1963) J. Biol. Chem. 238, 2797)PPi was also a competitive inhibitor with respect to ATP. A rate equation was derived to describe this inhibitory model for two competitive inhibitors where the binding of one inhibitor is contingent upon the binding of the other. The inhibition constants for a large number of nucleosides were then determined. It was found that the initial enzyme-inhibitor complex (of all nucleoside inhibitors) was slowly (0.2 min-1) transformed into a secondary (nondissociating) complex. The two inhibitory complexes appeared to exist in equilibrium. While decoyenine, N6-allyladenosine, and adenosine had similar inhibition constants for the initial complex (0.7 to 1.0 muM), their apparent inhibition constants for the secondary complex were 0.004, 0.06, and 0.5 muM respectively. These differences in the apparent dissociation constants from the secondary complexes are due to different equilibria between the initial and the secondary complexes. The ratios of the secondary complex to the initial complex at equilibrium were 3,250, 290, and 11 for decovenine, N6-allyladenosine, and adenosine, respectively.
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424
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Spector T, Beacham LM. Guanosine monophosphate synthetase from Escherichia coli B-96. Inhibition by nucleosides. J Biol Chem 1975. [DOI: 10.1016/s0021-9258(19)41600-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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425
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Spector T, Miller RL, Fyfe JA, Krenitsky TA. GMP synthetase from Escherichia coli B-96. Interactions with substrate analogs. BIOCHIMICA ET BIOPHYSICA ACTA 1974; 370:585-91. [PMID: 4613384 DOI: 10.1016/0005-2744(74)90120-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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