Sulfur isotope effects in the hydrogen ion decomposition of polythionates

1967 ◽  
Vol 45 (2) ◽  
pp. 181-187 ◽  
Author(s):  
U. Agarwala ◽  
C. E. Rees ◽  
H. G. Thode
Keyword(s):  
Sulfur Isotope ◽  
Isotope Effects ◽  
Experimental Results ◽  
Hydrogen Ion ◽  
Rate Controlling Step ◽  
Sulfur Bond

The sulfur isotope effects in the decomposition of tri-, tetra-, and penta-thionate have been studied. There are three distinct intermolecular and three distinct intramolecular isotope effects. The experimental results show that the decomposition of these polythionates may be described in terms of a model where the rate-controlling step is the cleavage of a sulfur–sulfur bond, and that the appropriate cleavage forms are (S2O32−) (SO3), (S3O3) (SO32−), and (S4O3) (SO32−) for tri-, tetra-, and penta-thionate, respectively.

SULFUR ISOTOPE EFFECTS IN THE HYDROGEN ION DECOMPOSITION OF THIOSULFATE

1965 ◽  
Vol 43 (10) ◽  
pp. 2802-2811 ◽  
Author(s):  
U. Agarwala ◽  
C. E. Rees ◽  
H. G. Thode
Keyword(s):  
Sulfur Isotope ◽  
Isotope Effects ◽  
Hydrogen Ion ◽  
Decomposition Mechanisms ◽  
Good Agreement

Sulfur isotope effects in the decomposition of thiosulfate have been studied. There are two distinct intermolecular isotope effects and these have been used to examine various mechanisms for the reaction. By use of the theory of competing isotope reactions the thiosulfate decomposition mechanisms of La Mer and Davis have been shown to predict isotope effects not in accord with experiment, while a simple bimolecular three-centered reaction has been shown to predict sulfur and sulfite isotope effects in good agreement with the experimentally determined values of 1.9% and 0.9%.

Untersuchungen zur Reaktion der Alkoholdehydrogenase mit Tritium-markierten Substraten

1966 ◽  
Vol 21 (6) ◽  
pp. 540-546 ◽  
Author(s):  
Dieter Palm
Keyword(s):  
Alcohol Dehydrogenase ◽  
Temperature Dependence ◽  
Isotope Effect ◽  
Substrate Binding ◽  
Isotope Effects ◽  
Direct Interaction ◽  
Enzyme Complex ◽  
Temperature Range ◽  
Yeast Alcohol Dehydrogenase ◽  
Rate Controlling Step

Unexpectedly, the isotope effect of ethanol-1-Τ as a substrate of yeast alcohol dehydrogenase, increases with rising temperature from kH/kT = 3.2 at 5 —15°C to 3.8—4.7 at 20 —35 °C. This suggests a change of the rate controlling step as proposed by MÜLLER-HILL and WALLENFELS, who investigated the temperature dependence of the activation energies in this temperature range. A comparison of the affinities of propanol and butanol with the isotope effects of the corresponding tritium labelled compounds (propanol-1-Τ 6.7 at 25 °C, butanol-1-Τ 6.8 at 25 °C) supports the proposal, that during substrate binding, there must be a direct interaction between the enzyme complex and hydrogen which is removed in the reaction. These influences are less pronounced for the ethanol homologues which are bound less tightly to the enzyme. Therefore the H transfering step proper gives a greater contribution to the overall experimental isotope effect.

Model calculations of isotope effects. VII. Deprotonation of 2-nitropropane by oxy anion bases

1983 ◽  
Vol 36 (8) ◽  
pp. 1503
Author(s):  
DJ McLennan
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Isotope Effects ◽  
Experimental Results ◽  
Electron Delocalization ◽  
Model Calculations ◽  
Charge Delocalization ◽  
Successful Model ◽  
Deuterium Isotope Effects ◽  
State Models

Model calculations of primary and secondary deuterium isotope effects for the hydroxide-induced deprotonation of 2-nitropropane are reported. Various transition-state models have been examined in an effort to reproduce experimental results. A purely pyramidal transition state in which proton transfer has run far ahead of carbon rehybridization and charge delocalization is a successful model as far as isotope effects are concerned, but may fail on other counts. Three incipient trigonal models for the transition state have been tested, and, although none can be firmly eliminated by the resultant isotope effects, those involving the proton transfer's running ahead of electron delocalization and perhaps carbon rehybridization are favoured.

Stable isotope fractionation by Clostridium pasteurianum. 4. Sulfur isotope fractionation during enzymatic S3O62−, S2O32−, and SO32− reductions

1981 ◽  
Vol 27 (8) ◽  
pp. 824-834
Author(s):  
G. I. Harrison ◽  
E. J. Laishley ◽  
H. R. Krouse
Keyword(s):  
Stable Isotope ◽  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Isotope Effects ◽  
Growth Conditions ◽  
Enzyme Concentration ◽  
Clostridium Pasteurianum ◽  
Relative Reduction ◽  
Stable Isotope Fractionation ◽  
Sulfur Isotope Fractionation

Cell-free extracts from Clostridium pasteurianum grown on SO32− utilize H2 to reduce S3O62−, S2O32−, and SO32− to H2S at a much faster rate than extracts from SO42−-grown cells. This further supports the concept of an inducible dissimilatory type SO32− reductive pathway in this organism. 35S dilution experiments further support the concept that S3O62− and S2O32− are pathway intermediates. The inducible SO32− reductase is ferredoxin linked and the kinetics of the reduction and the sulfur isotope fractionation of the product can be altered by altering the growth conditions. The attending sulfur isotope fractionations are similar to those observed during the chemical decomposition of these compounds. In the case of S2O32−, 35S labelling experiments verified the conclusions derived from the stable isotope fractionation data concerning the relative reduction rates of the sulfane and sulfonate sulfurs. The reduction rates were also affected by enzyme concentration. The integrity of the whole cell is a necessary requirement for the large inverse isotope effects previously reported.

Thiosulfate formation and associated isotope effects during sulfite reduction by Clostridium pasteurianum

1979 ◽  
Vol 25 (6) ◽  
pp. 719-721 ◽  
Author(s):  
L. A. Chambers ◽  
P. A. Trudinger
Keyword(s):  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Isotope Effects ◽  
Clostridium Pasteurianum ◽  
Stages Of Growth ◽  
Bacterial Cultures ◽  
Sulfur Isotope Fractionation ◽  
Secondary Chemical Reaction ◽  
Secondary Chemical ◽  
Isotopic Effects

During growth of Clostridium pasteurianum on sulfite, approximately half the sulfite was reduced to sulfide and half to thiosulfate. Sulfide was enriched in 32S or 34S at different stages of growth and thiosulfate was enriched in 32S, particularly in the sulfane atom.It is suggested that thiosulfate in these bacterial cultures arose from a secondary chemical reaction. The chemical formation of thiosulfate from sulfide and sulfite was also accompanied by sulfur isotope fractionation. The implications of these results with respect to 'inverse' isotopic effects are discussed.

scholarly journals Effects of Iron and Nitrogen Limitation on Sulfur Isotope Fractionation during Microbial Sulfate Reduction

2012 ◽  
Vol 78 (23) ◽  
pp. 8368-8376 ◽  
Author(s):  
Min Sub Sim ◽  
Shuhei Ono ◽  
Tanja Bosak
Keyword(s):  
Nitrogen Fixation ◽  
Sulfate Reduction ◽  
Isotope Fractionation ◽  
Sulfur Isotope ◽  
Isotope Effects ◽  
Reducing Power ◽  
Sulfate Reducing ◽  
Microbial Sulfate Reduction ◽  
Sulfur Isotope Fractionation ◽  
S Isotope

ABSTRACTSulfate-reducing microbes utilize sulfate as an electron acceptor and produce sulfide that is depleted in heavy isotopes of sulfur relative to sulfate. Thus, the distribution of sulfur isotopes in sediments can trace microbial sulfate reduction (MSR), and it also has the potential to reflect the physiology of sulfate-reducing microbes. This study investigates the relationship between the availability of iron and reduced nitrogen and the magnitude of S-isotope fractionation during MSR by a marine sulfate-reducing bacterium, DMSS-1, aDesulfovibriospecies, isolated from salt marsh in Cape Cod, MA. Submicromolar levels of iron increase sulfur isotope fractionation by about 50% relative to iron-replete cultures of DMSS-1. Iron-limited cultures also exhibit decreased cytochromec-to-total protein ratios and cell-specific sulfate reduction rates (csSRR), implying changes in the electron transport chain that couples carbon and sulfur metabolisms. When DMSS-1 fixes nitrogen in ammonium-deficient medium, it also produces larger fractionation, but it occurs at faster csSRRs than in the ammonium-replete control cultures. The energy and reducing power required for nitrogen fixation may be responsible for the reverse trend between S-isotope fractionation and csSRR in this case. Iron deficiency and nitrogen fixation by sulfate-reducing microbes may lead to the large observed S-isotope effects in some euxinic basins and various anoxic sediments.

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