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Effects of high hydrostatic pressure or hydrophobic modification on thermal stability of xanthine oxidase. Enzyme Microb Technol 2017; 103:18-24. [DOI: 10.1016/j.enzmictec.2017.04.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 04/15/2017] [Accepted: 04/21/2017] [Indexed: 11/22/2022]
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Some Recent Developments in the Study of Paramagnetic Species of Biological Interest. ADVANCES IN CHEMICAL PHYSICS 2007. [DOI: 10.1002/9780470143537.ch16] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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Bray RC. The reactions and the structures of molybdenum centers in enzymes. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2006; 51:107-65. [PMID: 6255771 DOI: 10.1002/9780470122969.ch3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Beinert H, Palmer G. Contributions of EPR spectroscopy to our knowledge of oxidative enzymes. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2006; 27:105-98. [PMID: 4303031 DOI: 10.1002/9780470122723.ch3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Kenner GH, Brik AB, Liu G, Haskell EH, Hayes RB, Knight JA, Vajda EG, Miller SC, Jee WSS, Barrus JK. Variation of long-lived free radicals responsible for the EPR native signal in bone of aged or diseased human females and ovariectomized adult rats. RADIAT MEAS 2005; 39:255-62. [PMID: 15884170 DOI: 10.1016/j.radmeas.2004.01.040] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The purpose of this study was to gain insights into the variations seen in the electron paramagnetic resonance (EPR) spectroscopy of the native signals of teeth and bones used for retrospective dosimetry measurements. We determined that changes occur in the long-lived free radicals responsible for the native signal of cortical bone in aging or diseased human females and aged ovariectomized rats. This was done by measuring the magnitude of the broad (BC) and narrow (NC) components of the native EPR signal of bone following chemical extraction, aging, crushing and thermal annealing. Bone from the upper midshaft of femora of young (17-34 years old, n=5) and elderly (70-92 years old, n=18) females was examined. The results showed that the elderly women had significantly higher BC than the younger women (P<0.01). A similar interpretation was made of the data from an aging female rat osteoporosis model. The results for the NC signals were similar. Finally, dramatic decreases in both NC and BC signals were seen in HIV positive and uncontrolled diabetic (one each) patients indicating the need for studying this signal for a broad spectrum of metabolic disorders. Experiments were performed which strongly indicate that iron liganded with organic molecules is the source of the BC signal. Finally, the accuracy achieved in this study indicates that resolving the dosimetric signal (g=2.0018) should be improved by subtraction of the deconvoluted NC and BC signals from the original spectrum.
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Affiliation(s)
- G H Kenner
- Division of Radiobiology, School of Medicine, University of Utah, Salt Lake City, UT 84112, USA.
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RAJAGOPALAN KV, ALEMAN V, HANDLER P, HEINEN W, PALMER G, BEINERT H. Electron paramagnetic resonance studies of iron reduction and semiquinone formation in metalloflavoproteins. Biochem Biophys Res Commun 1998; 8:220-6. [PMID: 14489969 DOI: 10.1016/0006-291x(62)90267-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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BRAY RC. The chemistry of xanthine oxidase. 8. Electronspin-resonance measurements during the enzymic reaction. Biochem J 1998; 81:196-9. [PMID: 13872670 PMCID: PMC1243317 DOI: 10.1042/bj0810196] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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SHETHNA YI, WILSON PW, HANSEN RE, BEINERT H. IDENTIFICATION BY ISOTOPIC SUBSTITUTION OF THE EPR SIGNAL AT G = 1.94 IN A NON-HEME IRON PROTEIN FROM AZOTOBACTER. Proc Natl Acad Sci U S A 1996; 52:1263-71. [PMID: 14231451 PMCID: PMC300434 DOI: 10.1073/pnas.52.5.1263] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Abstract
It was deduced many years ago from indirect evidence that demolybdo xanthine oxidase is present in normal bovine milk. This has now been confirmed by isolation of this enzyme form by a method based on the folate-gel affinity-chromatography procedure described Nishino & Tsushima [(1986) J. Biol. Chem. 261, 11242-11246]. Enzymic and spectroscopic properties of demolybdo xanthine oxidase, which retains flavin and iron-sulphur centres, are generally in accordance with expectations. Like the normal enzyme, it yields on denaturation material fluorescing at 460 nm. Molybdenum cofactor activity measured by the Neurospora crassa nit-1 assay in the presence of added molybdate was 33% of that of the normal enzyme. The absorption spectrum in the near-u.v. region differs slightly, but significantly, from that of the active and desulpho forms of the enzyme. It is concluded that the molybdenum cofactor site contains a pterin-like material not identical with that in the normal enzyme. The significance of the occurrence of demolybdo xanthine oxidase in milk is discussed, and evidence in the literature for demolybdo forms of other molybdoenzymes is briefly reviewed. Additional studies on the use of the affinity procedure for large-scale preparation of high-activity xanthine oxidase are described. In agreement with our ability to isolate the demolybdo enzyme, the procedure appears less effective in eliminating the demolybdo than the desulpho enzyme.
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Affiliation(s)
- A M Ventom
- School of Chemistry and Molecular Sciences, University of Sussex, Falmer, Brighton, U.K
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Barber MJ, Bray RC, Cammack R, Coughlan MP. Oxidation--reduction potentials of turkey liver xanthine dehydrogenase and the origins of oxidase and dehydrogenase behaviour in molybdenum-containing hydroxylases. Biochem J 1977; 163:279-89. [PMID: 869927 PMCID: PMC1164694 DOI: 10.1042/bj1630279] [Citation(s) in RCA: 44] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Redox potentials for the various centres in the enzyme xanthine dehydrogenase (EC 1.2.1.37) from turkey liver determined by potentiometric titration in the presence of mediator dyes, with low-temperature electron-paramagnetic-resonance spectroscopy. Values at 25 degrees C in pyrophosphate buffer, pH 8.2, are: Mo(VI)/Mo(V)(Rapid),-350 +/- 20mV; Mo(V) (Rapid)/Mo(IV), -362 +/- 20mV; Fe-S Iox./Fe-S Ired., -295 +/- 15mV; Fe-S IIox./Fe-S IIred., -292 +/- 15mV; FAD/FADH,-359+-20mV; FADH/FADH2, -366 +/- 20mV. This value of the FADH/FADH2 potential, which is 130mV lower than the corresponding one for milk xanthine oxidase [Cammack, Barber & Bray (1976) Biochem. J. 157, 469-478], accounts for many of the differences between the two enzymes. When allowance is made for some interference by desulpho enzyme, then differences in the enzymes' behaviour in titration with xanthine [Barber, Bray, Lowe & Coughlan (1976) Biochem. J. 153, 297-307] are accounted for by the potentials. Increases in the molybdenum potentials of the enzymes caused by the binding of uric acid are discussed. Though the potential of uric acid/xanthine (-440mV) is favourable for full reduction of the dehydrogenase, nevertheless, during turnover, for kinetic reasons, only FADH and very little FADH2 is produced from it. Since only FADH2 is expected to react with O2, lack of oxidase activity by the dehydrogenase is explained. Reactivity of the two enzymes with NAD+ as electron acceptor is discussed in relation to the potentials.
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Barber MJ, Bray RC, Lowe DJ, Coughlan MP. Studies by electron-paramagnetic-resonance spectroscopy and stopped-flow spectrophotometry on the mechanism of action of turkey liver xanthine dehydrogenase. Biochem J 1976; 153:297-307. [PMID: 179533 PMCID: PMC1172575 DOI: 10.1042/bj1530297] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Studies by e.p.r. (electron-paramagnetic-resonance) spectroscopy and by stopped-flow spectrophotometry on turkey liver xanthine dehydrogenase revealed strong similarities to as well as important differences from the Veillonella alcalescens xanthine dehydrogenase and milk xanthine oxidase. The turkey enzyme is contaminated by up to three non-functional forms, giving molybdenum e.p.r. signals designated Resting I, Resting II and Slow. Slow and to a lesser extent Resting I signals are like those from the Veillonella enzyme, whereas Resting II is very like a resting signal described by K. V. Rajagopolan, P. Handler, G. Palmer & H. Beinert (1968) (J. Biol. Chem. 243, 3784-3796) for aldehyde oxidase. Another non-functional form that gives the Inhibited signal is produced on treatment of the enzyme with formaldehyde. Stopped-flow measurements at 450 nm show that, as for the milk enzyme, reduction by xanthine is rate-limiting in enzyme turnover. The active enzyme gives rise to Very Rapid and Rapid molybdenum(V) e.p.r. signals, as well as to an FADH signal. That these signals are almost indistinguishable from those of the milk enzyme, confirms the similarities between the active sites. There are two types of iron-sulphur centres that give signals like those in the milk enzyme, though with slightly different parameters. Quantitative reduction titration of the functional enzyme with xanthine revealed two important differences between the turkey and the milk enzymes. First, the turkey enzyme FADH/FADH2 system has a redox potential sufficiently low that xanthine is incapable of reducing the flavin completely. This finding presumably explains the very low oxidase activity. Secondly, whereas the Fe/S II chromophore in the milk enzyme has a relatively high redox potential, for the turkey enzyme the value of this potential is lower and similar to that of its Fe/S I chromophore.
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Blumberg WE, Peisach J. On the interpretation of electron paramagnetic resonance spectra of binuclear iron-sulfur proteins. Arch Biochem Biophys 1974; 162:502-12. [PMID: 4366147 DOI: 10.1016/0003-9861(74)90210-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Lowe DJ, Lynden-Bell RM, Bray RC. Spin-spin interaction between molybdenum and one of the iron-sulphur systems of xanthine oxidase and its relevance to the enzymic mechanism. Biochem J 1972; 130:239-49. [PMID: 4347785 PMCID: PMC1174321 DOI: 10.1042/bj1300239] [Citation(s) in RCA: 99] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
1. Electron-paramagnetic-resonance (e.p.r.) studies at 9 and 35GHz at helium temperatures have given new information relating to the structure and mechanism of action of xanthine oxidase. 2. As reported by others, the enzyme gives two types of e.p.r. signal attributed to iron-sulphur systems. The first has g(av.)=1.95. Parameters of the second are determined as g(1) 2.12, g(2) 2.007 and g(3) 1.91, with g(av.)=2.01. This species seems to have a slightly higher redox potential than the former one. 3. Temperature-dependent changes in the form of Mo(v) e.p.r. signals from the enzyme, observed under certain conditions, are shown to be due to weak spin-spin interaction between Mo(v) and g(av.)=1.95 Fe/S. The phenomenon has been studied most fully for the Slow Mo(v) signal. Here, the spectral change takes the form of an additional approximately isotropic 11G splitting, detected below about 45 degrees K only. Samples without Fe/S reduced showed no such changes of spectrum. 4. Similar spectral changes were observed in the Rapid Mo(v) signals, obtained in rapid-freezing experiments, but only in samples corresponding to relatively long reaction times with the substrate. It is suggested therefore that the phenomenon may provide a means of distinguishing enzyme centres with Mo only reduced from those in which both Mo and Fe/S are reduced. 5. Additional rapid-freezing data tending to support a two- rather than a one-electron transfer of reducing equivalents from substrates to xanthine oxidase are reported.
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Swann JC, Bray RC. Multiple phases in the reduction of xanthine oxidase by substrates. EUROPEAN JOURNAL OF BIOCHEMISTRY 1972; 26:407-15. [PMID: 4338679 DOI: 10.1111/j.1432-1033.1972.tb01781.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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18
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Massey V, Edmondson D, Palmer G, Beacham LM, Elion GB. The separation of functional and non-functional xanthine oxidase by affinity chromatography. Biochem J 1972; 127:10P-11P. [PMID: 4672853 PMCID: PMC1178622 DOI: 10.1042/bj1270010p] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Hollocher TC, Ehrenberg A. Magnetic susceptibility of succinate dehydrogenase: the 4-iron preparation. BIOCHIMICA ET BIOPHYSICA ACTA 1971; 253:346-51. [PMID: 4332304 DOI: 10.1016/0005-2728(71)90038-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Massey V, Komai H, Palmer G, Elion GB. The existence of nonfunctional active sites in milk xanthine oxidase: reaction with functional active site inhibitors. VITAMINS AND HORMONES 1971; 28:505-31. [PMID: 4335890 DOI: 10.1016/s0083-6729(08)60909-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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[136] Polarography of flavins. Methods Enzymol 1971. [DOI: 10.1016/s0076-6879(71)18093-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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22
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Pick FM, McGartoll MA, Bray RC. Reaction of formaldehyde and of methanol with xanthine oxidase. EUROPEAN JOURNAL OF BIOCHEMISTRY 1971; 18:65-72. [PMID: 4322209 DOI: 10.1111/j.1432-1033.1971.tb01215.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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McGartoll MA, Pick FM, Swann JC, Bray RC. Properties of xanthine oxidase preparations dependent on the proportions of active and inactivated enzyme. BIOCHIMICA ET BIOPHYSICA ACTA 1970; 212:523-6. [PMID: 4318599 DOI: 10.1016/0005-2744(70)90264-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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25
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On the Mechanism of Inactivation of Xanthine Oxidase by Allopurinol and Other Pyrazolo[3,4-d]pyrimidines. J Biol Chem 1970. [DOI: 10.1016/s0021-9258(18)63065-0] [Citation(s) in RCA: 301] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Abstract
The composition of milk xanthine oxidase has been reinvestigated. When the enzyme is prepared by methods that include a selective denaturation step in the presence of sodium salicylate the product is obtained very conveniently and in high yield, and is homogeneous in the ultracentrifuge and in recycling gel filtration. It has specific activity higher than previously reported preparations of the enzyme and its composition approximates closely to 2mol of FAD, 2g-atoms of Mo and 8g-atoms of Fe/mol of protein (molecular weight about 275000). In contrast, when purely conventional preparative methods are used the product is also homogeneous by the above criteria but has a lower specific activity and is generally comparable to the crystallized enzyme described previously. Such samples also contain 2mol of FAD/mol of protein but they have lower contents of Mo (e.g. 1.2g-atom/mol). Amino acid compositions for the two types of preparation are indistinguishable. These results confirm the previous conclusion that conventional methods give mixtures of xanthine oxidase with an inactive modification of the enzyme now termed ;de-molybdo-xanthine oxidase', and show that salicylate can selectively denature the latter. The origin of de-molybdo-xanthine oxidase was investigated. FAD/Mo ratios show that it is present not only in enzyme purified by conventional methods but also in ;milk microsomes' (Bailie & Morton, 1958) and in enzyme samples prepared without proteolytic digestion. We conclude that it is secreted by cows together with the active enzyme and we discuss its occurrence in the preparations of other workers. Studies on the milks of individual cows show that nutritional rather than genetic factors determine the relative amounts of xanthine oxidase and de-molybdo-xanthine oxidase. A second inactive modification of the enzyme, now termed ;inactivated xanthine oxidase', causes variability in activity relative to E(450) or to Mo content and formation of it decreases these ratios during storage of enzyme samples including samples free from demolybdo-xanthine oxidase. We conclude that even the best purified xanthine oxidase samples described here and by other workers are contaminated by significant amounts of the inactivated form. This may complicate the interpretation of changes in the enzyme taking place during the slow phase of reduction by substrates. Attempts to remove iron from the enzyme by published methods were not successful.
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Palmer G, Massey V. Electron Paramagnetic Resonance and Circular Dichroism Studies on Milk Xanthine Oxidase. J Biol Chem 1969. [DOI: 10.1016/s0021-9258(18)83444-5] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Rajagopalan KV, Handler P, Palmer G, Beinert H. Studies of Aldehyde Oxidase by Electron Paramagnetic Resonance Spectroscopy. J Biol Chem 1968. [DOI: 10.1016/s0021-9258(18)92014-4] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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32
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Rajagopalan KV, Handler P, Palmer G, Beinert H. Studies of Aldehyde Oxidase by Electron Paramagnetic Resonance Spectroscopy. J Biol Chem 1968. [DOI: 10.1016/s0021-9258(18)92015-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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33
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Aleman V, Handler P, Palmer G, Beinert H. Studies on Dihydroorotate Dehydrogenase by Electron Paramagnetic Resonance Spectroscopy. J Biol Chem 1968. [DOI: 10.1016/s0021-9258(18)93411-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Gibson JF, Bray RC. Electron spin resonance of non-haem iron in xanthine oxidase. BIOCHIMICA ET BIOPHYSICA ACTA 1968; 153:721-3. [PMID: 4297065 DOI: 10.1016/0005-2728(68)90201-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Hart LI, Owen EC, Proudfoot R. The influence of dietary molybdenum on the xanthine oxidase activity of the milk of ruminants. Br J Nutr 1967; 21:617-30. [PMID: 6052879 DOI: 10.1079/bjn19670065] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
1.The oral administration of sodium molybdate caused a rapid rise of molybdenum in the milk of cows and goats fed on a low-molybdenum diet, but did not affect the xanthine oxidase activities of the milk of either species.2.In the milks of cows not dosed with sodium molybdate, the regression of the xanthin oxidase activity (y) on the molybdenum content (x) was found to be y = 170.7x+43.86 (r = +0.9386; P < 0.0001), suggesting that all the molybdenum of such milk is bound to enzymically active xanthine oxidase.3.The molybdenum contents of the milk of goats not does with sodium molybdate varied from animal to anumal and the xanthine oxidase activites were much lower than those of cow' milk. there was no correlation between xanthine oxidase activity and the molybdenum contend of the milks of the goats.4. These results are discussed in relation to previous work of the authors and others.
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Johnson CE, Knowles PF, Bray RC. Mössbauer evidence on the form of iron in xanthine oxidase. Biochem J 1967; 103:10contd-12c. [PMID: 6033752 PMCID: PMC1270403 DOI: 10.1042/bj1030010c] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Meriwether LS, Marzluff WF, Hodgson WG. Molybdenum-thiol complexes as models for molybdenum bound in enzymes. Nature 1966; 212:465-7. [PMID: 4291150 DOI: 10.1038/212465a0] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Bray RC, Meriwether LS. Electron spin resonance of xanthine oxidase substituted with molybdenum-95. Nature 1966; 212:467-9. [PMID: 4291151 DOI: 10.1038/212467a0] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Abstract
1. The reaction of milk xanthine oxidase with iodoacetamide has been studied with the silver-silver iodide electrode. 2. The reaction proceeds considerably faster in the presence of xanthine than in its absence. Anaerobically, with excess of xanthine, the reaction takes place as a rapid phase in which the enzyme is inactivated and in which approx. 1 thiol group/mol. of enzyme reacts and as a slower phase in which about 12 groups/mol. react. 3. The rapid reaction appears to be first-order with respect to xanthine oxidase and iodoacetamide and independent of the xanthine concentration with more than about 3mol. of xanthine/mol. of enzyme. 4. The velocity constant of the rapid phase is 0.26min.(-1) at 25 degrees and pH7.0, with 1mm-iodoacetamide and 17mum-xanthine oxidase. The velocity constant for the slower phase is about one-hundredth of this value. 5. The velocities of both phases increase with increasing pH in the range 5.0-9.6. 6. Xanthine may be replaced by salicylaldehyde without affecting the rate of loss of enzymic activity. With sodium dithionite as reducing agent, the reaction is slightly faster. 7. The possible function of thiol groups in the reaction mechanism of the enzyme is discussed.
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Brumby PE, Miller RW, Massey V. The Content and Possible Catalytic Significance of Labile Sulfide in Some Metalloflavoproteins. J Biol Chem 1965. [DOI: 10.1016/s0021-9258(18)97450-8] [Citation(s) in RCA: 120] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Tavlitzki J. [Molybdenum in biology. I. Role of molybdenum in metabolic processes]. EXPERIENTIA 1965; 21:177-88. [PMID: 5320883 DOI: 10.1007/bf02141875] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Kinetic Studies on Reduced Diphosphopyridine Nucleotide Dehydrogenase by Electron Paramagnetic Resonance Spectroscopy. J Biol Chem 1965. [DOI: 10.1016/s0021-9258(18)97675-1] [Citation(s) in RCA: 71] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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EHRENBERG A, BRAY RC. Magnetic susceptibility changes and electron spin resonance signals related to the iron of xanthine oxidase. Arch Biochem Biophys 1965; 109:199-202. [PMID: 14281948 DOI: 10.1016/0003-9861(65)90309-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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46
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Andrews P, Bray RC, Edwards P, Shooter KV. The chemistry of xanthine oxidase. 11. Ultracentrifuge and gel-filtration studies on the milk enzyme. Biochem J 1964; 93:627-32. [PMID: 5839197 PMCID: PMC1214020 DOI: 10.1042/bj0930627] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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Totter JR. THE QUANTUM YIELD OF THE CHEMILUMINESCENCE OF DIMETHYLBIACRIDYLIUM NITRATE AND THE MECHANISM OF ITS ENZYMICALLY INDUCED CHEMILUMINESCENCE*. Photochem Photobiol 1964. [DOI: 10.1111/j.1751-1097.1964.tb08779.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Bray RC, Palmer G, Beinert H. Direct Studies on the Electron Transfer Sequence in Xanthine Oxidase by Electron Paramagnetic Resonance Spectroscopy. J Biol Chem 1964. [DOI: 10.1016/s0021-9258(18)93903-7] [Citation(s) in RCA: 83] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Direct Studies on the Electron Transfer Sequence in Xanthine Oxidase by Electron Paramagnetic Resonance Spectroscopy. J Biol Chem 1964. [DOI: 10.1016/s0021-9258(18)93902-5] [Citation(s) in RCA: 106] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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