A structural study of sodium dithionite and its ephemeral dihydrate: A new conformation for the dithionite ion

The kinetics of reduction of indigocarmine-dye-oxidized Fe protein of nitrogenase from Klebsiella pneumoniae (Kp2ox) by sodium dithionite in the presence and absence of MgADP were studied by stopped-flow spectrophotometry at 23 degrees C and at pH 7.4. Highly co-operative binding of 2MgADP (composite K greater than 4 × 10(10) M-2) to Kp2ox induced a rapid conformation change which caused the redox-active 4Fe-4S centre to be reduced by SO2-.(formed by the predissociation of dithionite ion) with k = 3 × 10(6) M-1.s-1. This rate constant is at least 30 times lower than that for the reduction of free Kp2ox (k greater than 10(8) M-1.s-1). Two mechanisms have been considered and limits obtained for the rate constants for MgADP binding/dissociation and a protein conformation change. Both mechanisms give rate constants (e.g. MgADP binding 3 × 10(5) less than k less than 3 × 10(6) M-1.s-1 and protein conformation change 6 × 10(2) less than k less than 6 × 10(3) s-1) that are similar to those reported for creatine kinase (EC 2.7.3.2). The kinetics also show that in the catalytic cycle of nitrogenase with sodium dithionite as reductant replacement of 2MgADP by 2MgATP occurs on reduced and not oxidized Kp2. Although the Kp2ox was reduced stoichiometrically by SO2-. and bound two equivalents of MgADP with complete conversion into the less-reactive conformation, it was only 45% active with respect to its ability to effect MgATP-dependent electron transfer to the MoFe protein.

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The structure of sodium dithionite and the nature of the dithionite ion

Acta Crystallographica ◽

10.1107/s0365110x56001601 ◽

1956 ◽

Vol 9 (7) ◽

pp. 579-586 ◽

Cited By ~ 66

Author(s):

J. D. Dunitz

Keyword(s):

Sodium Dithionite ◽

Dithionite Ion

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Comment: On the Decomposition of Aqueous Sodium Dithionite

Canadian Journal of Chemistry ◽

10.1139/v71-186 ◽

1971 ◽

Vol 49 (7) ◽

pp. 1139-1140 ◽

Cited By ~ 4

Author(s):

L. Burlamacchi ◽

G. Guarini ◽

E. Tiezzi

Keyword(s):

Aqueous Solution ◽

Sodium Dithionite ◽

Aqueous Sodium ◽

Work Done ◽

Dithionite Ion

The mechanism proposed by M. Wayman and W. J. Lem for the decomposition of dithionite ion in aqueous solution is reconsidered in the light of previous work done by the authors.

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Rate of reaction of dithionite ion with oxygen in aqueous solution

Journal of Applied Physiology ◽

10.1152/jappl.1964.19.3.522 ◽

1964 ◽

Vol 19 (3) ◽

pp. 522-525 ◽

Cited By ~ 17

Author(s):

J. A. Morello ◽

Margot R. Craw ◽

H. P. Constantine ◽

R. E. Forster

Keyword(s):

Aqueous Solution ◽

Reaction Rate ◽

Initial Rate ◽

Sodium Dithionite ◽

Zero Order ◽

Flowing Liquid ◽

First Order ◽

Rate Of Reaction ◽

Dithionite Ion ◽

Kinetics Of

The rate of removal of oxygen from aqueous solution by sodium dithionite in 0.1 m sodium hydroxide was studied in a rapid-reaction apparatus using a membrane-covered polarographic cell to determine Po2 in the flowing liquid. The measurements were made at 37 C, so that the data would be applicable in studies of the kinetics of oxyhemoglobin in blood. The initial concentrations in the mixed reacting solution were between 8 x 10-5 m and 47.5 x 10-5 m for dithionite, and either 10 x 10-5 m or 47.8 x 10-5 m for O2. The reaction over the first 40 msec was found to be first order with respect to dithionite and zero order with respect to molecular oxygen. The initial rate constant was 42.5 ± sd 3.6 sec-1. oxygen reduction by dithionite; hemoglobin; deoxygenation rate; dithionite-oxygen reaction rate Submitted on June 17, 1963

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The vanadium- and molybdenum-containing nitrogenases of Azotobacter chroococcum. Comparison of mid-point potentials and kinetics of reduction by sodium dithionite of the iron proteins with bound magnesium adenosine 5′-diphosphate

Biochemical Journal ◽

10.1042/bj2510165 ◽

1988 ◽

Vol 251 (1) ◽

pp. 165-169 ◽

Cited By ~ 22

Author(s):

J Bergström ◽

R R Eady ◽

R N F Thorneley

Keyword(s):

Sodium Dithionite ◽

Azotobacter Chroococcum ◽

Effective Electron ◽

Iron Proteins ◽

Fe Protein ◽

Protein Components ◽

Dithionite Ion ◽

Kinetics Of ◽

Kinetics Of Reduction

The mid-point potentials of the Fe protein components (Ac2 and Ac2* respectively) of the Mo nitrogenase and V nitrogenase from Azotobacter chroococcum were determined in the presence of MgADP to be −450 mV (NHE) [Ac2(MgADP)2-Ac2*ox.(MgADP)2 couple] and −463 mV (NHE) [Ac2* (MgADP)2-Ac2*ox.(ADP)2 couple] at 23 degrees C at pH 7.2. These values are consistent with a flavodoxin characterized by Deistung & Thorneley [(1986) Biochem. J. 239, 69-75] with Em = −522 mV (NHE) being an effective electron donor to both the Mo nitrogenase and the V nitrogenase in vivo. Ac2*ox.(MgADP)2 and Ac2*ox.(MgADP)2 were reduced by SO2.- (formed by the predissociation of dithionite ion, S2O4(2-)) at similar rates, k = 4.7 × 10(6) +/- 0.5 × 10(6) M-1.s-1 and 3.2 × 10(6) +/- 0.2 × 10(6) M-1.s-1 respectively, indicating structural homology at the electron-transfer site associated with the [4Fe-4S] centre in these proteins.

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An Ultra-Structural Study of Human Melanoma in Vivo and Vitro

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100091275 ◽

1976 ◽

Vol 34 ◽

pp. 258-259

Author(s):

James R. Gaylor ◽

Fredda Schafer ◽

Robert E. Nordquist

Keyword(s):

Endoplasmic Reticulum ◽

Golgi Apparatus ◽

Protein Aggregation ◽

Structural Study ◽

Human Melanoma ◽

Protein Matrix ◽

Early Form ◽

Endoplasmic Reticulum Protein ◽

Mitochondrial Origin

Several theories on the origin of the melanosome exist. These include the Golgi origin theory, in which a tyrosinase-rich protein is "packaged" by the Golgi apparatus, thus forming the early form of the melanosome. A second theory postulates a mitochondrial origin of melanosomes. Its author contends that the melanosome is a modified mitochondria which acquires melanin during its development. A third theory states that a pre-melanosome is formed in the smooth or rough endoplasmic reticulum. Protein aggregation is suggested by one author as a possible source of the melanosome. This fourth theory postulates that the melanosome originates when the protein products of several genetic loci aggregate in the cytoplasm of the melanocyte. It is this protein matrix on which the melanin is deposited. It was with these theories in mind that this project was undertaken.

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