scholarly journals The molybdenum centre of native xanthine oxidase. Evidence for proton transfer from substrates to the centre and for existence of an anion-binding site

1978 ◽  
Vol 175 (3) ◽  
pp. 869-878 ◽  
Author(s):  
S Gutteridge ◽  
S J Tanner ◽  
R C Bray
Keyword(s):  
Xanthine Oxidase ◽  
Anion Binding ◽  
Hydrogen Atoms ◽  
Substrate Molecule ◽  
Strongly Coupled ◽  
Exchange Processes ◽  
Turnover Process ◽  
Anion Site ◽  
A Site

The observation by Bray & Knowles [Proc. R. Soc. London Ser. A (1968) 302, 351–353] of direct transfer, during the catalytic reaction, of hydrogen atoms from substrate molecules to the enzyme xanthine oxidase was reinvestigated. The experimental phenomenon and its basic interpretation were confirmed and extended. In the reduced functional enzyme, molybdenum(V) interacts with two enzyme-bound protons, which are exchangeable with solvent protons. One of these is coupled to the metal with AHav. 1.4mT and the other with AHav. 0.3mT. The molecule also contains a site for the binding of anions, presumably as ligands of molybdenum. This is shown by effects of nitrate ions on the e.p.r. spectra. The spectra of the nitrate and 1-methylxanthine complexes of the reduced enzyme are very similar to one another, and are designated Rapid type-1 spectra. It is concluded that, in the Michaelis complex, the substrate molecule occupies the anion site, probably being bound to molybdenum via the nitrogen in its 9-position. During the turnover process, hydrogen from the substrate C-8 position, after transfer to the enzyme, appears as the proton more strongly coupled to molybdenum. This proton then exchanges with solvent deuterium with a rate constant of 27s-1, at pH 8.2 and 12 degrees C. It has been confirmed that substrate molecules occupying the anion site do not interfere with observation of the transfer and exchange processes.

scholarly journals Comparison of the molybdenum centres of native and desulpho xanthine oxidase. The nature of the cyanide-labile sulphur atom and the nature of the proton-accepting group

1978 ◽  
Vol 175 (3) ◽  
pp. 887-897 ◽  
Author(s):  
S Gutteridge ◽  
S J Tanner ◽  
R C Bray
Keyword(s):  
Exchange Rate ◽  
Xanthine Oxidase ◽  
Catalytic Reaction ◽  
Functional Form ◽  
Great Majority ◽  
Sulphur Atom ◽  
Strongly Coupled ◽  
Weakly Coupled ◽  
Exchange Rate Constant ◽  
A Site

The non-functional form of xanthine oxidase known as the desulpho enzyme was compared with the functional enzyme in various ways, to obtain information on the structure of the molybdenum centre and the mechanism of the catalytic reaction. The desulpho enzyme, like the functional one, possesses a site for the binding of anions, presumably as ligands of molybdenum. Evidence is presented that in the Mo(V) e.p.r. signal from the desulpho-enzyme, as in that from the functional enzyme, a weakly coupled proton, in addition to a strongly coupled proton, interacts with the metal. Measurements were carried out by e.p.r. on the rate at which the proton strongly coupled to molybdenum exchanged, on diluting enzyme samples with 2H2O. For the desulpho enzyme the exchange rate constant was 0.40s-1, at pH 8.2 and 12 degrees C, and for the functional enzyme it was 85 s-1. It is shown that the great majority of reported differences between the enzyme forms are consistent with functional enzyme containing an (Enzyme)-Mo=S grouping, replaced in the desulpho form by (Enzyme)-Mo=O. Protonation of these groups, with pK values of about 8 and 10 respectively, would give (Enzyme)-Mo-SH and (Enzyme)-Mo-OH, these being the forms observed by e.p.r. The accepting group in the functional enzyme, for the proton transferred from the substrate while molybdenum is reduced in the catalytic reaction [Gutteridge, Tanner & Bray (1978) Biochem J. 175 869-878], is thus taken to be Mo=S.

scholarly journals Na2MoO2−δF4+δ – a perovskite with a unique combination of atomic orderings and octahedral tilts

2015 ◽  
Vol 51 (84) ◽  
pp. 15469-15471 ◽  
Author(s):  
Hajime Ishikawa ◽  
Irene Munaò ◽  
Bela E. Bode ◽  
Zenji Hiroi ◽  
Philip Lightfoot
Keyword(s):  
Unique Combination ◽  
System P ◽  
Anion Site ◽  
A Site

Na2MoO2−δF4+δ represents the first example of a perovskite exhibiting simultaneous A-site, B-site and anion site order, together with a complex tilt system.

scholarly journals Changes of LISM Characteristics in the Heliospheric Interface

1984 ◽  
Vol 81 ◽  
pp. 28-31 ◽  
Author(s):  
Hartmut W. Ripken ◽  
Hans J. Fahr
Keyword(s):  
Solar System ◽  
Neutral Hydrogen ◽  
Solar Wind Plasma ◽  
Wind Vector ◽  
Hydrogen Atoms ◽  
Direct Inference ◽  
Degree Of Ionization ◽  
System Parameters ◽  
Exchange Processes ◽  
Heliospheric Interface

AbstractIt is possible to deduce LISM properties from observations of interstellar neutral gases in the inner solar system. Parameters accessible by this method are the interstellar wind vector and the densities and temperatures of hydrogen and helium, implying also the deduction of the relative abundance ratios and the degree of ionization in the LISM. Direct inference from observations, for example resonance luminescence measurements of Ly-alpha and He-58.4 nm radiation, yields values appropriate only for the inner solar system, i.e. for the regions within the heliopause dominated by the solar wind plasma.Particularly the subsonic LISM plasma interface ahead of the heliopause causes profound changes in the properties of the neutral LISM gas traversing this region. Mainly p-H charge exchange processes give rise to the destruction of primary hydrogen and the production of secondary hydrogen atoms, the net effect being a depletion of the neutral hydrogen component of the LISM by about 50%.Details on the depletion mechanisms, the hydrogen and oxygen extinctions, and the consequences for the Ly-alpha resonance luminescence intensity interpretations are presented.

Derangements and Laguerre polynomials

1976 ◽  
Vol 79 (1) ◽  
pp. 135-143 ◽  
Author(s):  
S. Even ◽  
J. Gillis
Keyword(s):  
Laguerre Polynomials ◽  
Type A ◽  
A Site

AbstractGiven a set consisting of n1, objects of type 1, n2 of type 2, …, nk of type k, we denote by the number of possible derangements of the set i.e. permutations in which no object occupies a site originally occupied by an object of the same type. A formula is found for in terms of Laguerre polynomials, and some of its implications are considered.

scholarly journals Relative roles of signals upstream of AAUAAA and promoter proximity in regulation of human immunodeficiency virus type 1 mRNA 3' end formation.

1992 ◽  
Vol 12 (12) ◽  
pp. 5555-5562 ◽  
Author(s):  
J D DeZazzo ◽  
J M Scott ◽  
M J Imperiale
Keyword(s):  
Human Immunodeficiency Virus ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Dependent Manner ◽  
Immunodeficiency Virus ◽  
A Site ◽  
The Impact ◽  
Hiv 1 ◽  
Rna Levels

At least two mechanisms have been implicated in regulating poly(A) site use in human immunodeficiency virus type 1 (HIV-1): inhibition of basal signals within 500 nucleotides (nt) of the cap site, leading to specific suppression of the 5' poly(A) site, and stimulation of basal signals by long terminal repeat U3 sequences, leading to specific activation of the 3' poly(A) site. We determined the relative contributions of these mechanisms in a HeLa cell transcription/processing reaction and by transient transfection analysis. In vitro, the efficiency of basal signals is equivalent close to (270 nt) and far from (1,080 nt) the promoter and is stimulated at least 30-fold in both positions by upstream U3 sequences. In vivo, U3 sequences also enhance processing at both positions. There are two additional effects when the poly(A) site is close to the cap site: at least a 15-fold reduction in total RNA levels and a 5-fold decrease in relative levels of RNA processed at the HIV-1 site in constructs containing U3. Both effects are overcome by insertion of upstream splicing signals in an orientation-dependent manner. Splicing appears to influence poly(A)+ RNA levels by two distinct mechanisms: stabilizing nuclear transcripts and directly stimulating 3' end formation. It is proposed that upstream elements play major roles in regulating poly(A) site choice and in controlling the subsequent fate of polyadenylated RNA. The impact of these findings on mechanisms of mRNA biogenesis in the HIV-1 provirus is discussed.

scholarly journals Description of a Nonlethal Herpes Simplex Virus Type 1 Glycoprotein D Deletion Mutant Affecting a Site Frequently Used for PCR

2000 ◽  
Vol 7 (2) ◽  
pp. 322-324 ◽  
Author(s):  
P. V. Coyle ◽  
S. Jain ◽  
D. Wyatt ◽  
C. McCaughey ◽  
H. J. O'Neill
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Virus Type ◽  
Herpes Simplex Virus Type ◽  
Deletion Mutant ◽  
Glycoprotein D ◽  
Nontranslated Region ◽  
Simplex Virus ◽  
A Site

ABSTRACT We report a herpes simplex virus type 1 mutant which failed to amplify with a commonly used glycoprotein D primer set. The virus contained a nine-base deletion in the gene's 5′ nontranslated region. The altered amplicon was clearly distinguishable on a 4% high-resolution agarose gel.

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