scholarly journals A pulse-radiolysis study of the manganese-containing superoxide dismutase from Bacillus stearothermophilus. A kinetic model for the enzyme action

1977 ◽  
Vol 165 (1) ◽  
pp. 71-79 ◽  
Author(s):  
M E McAdam ◽  
R A Fox ◽  
F Lavelle ◽  
E M Fielden
Keyword(s):  
Superoxide Dismutase ◽  
Pulse Radiolysis ◽  
Bacillus Stearothermophilus ◽  
Enzyme Concentration ◽  
Native Enzyme ◽  
Visible Absorption ◽  
Oxidation Reduction ◽  
Reduction Cycle ◽  
Computer Calculations ◽  
Kinetics Of

The enzymic reaction mechanism of a manganese-containing superoxide dismutase from Bacillus stearothermophilus was studied by using pulse radiolysis. During catalysis (pH 8.9; 25 degrees C), changes occurring in the kinetics of substrate disappearance and in the visible absorption of the enzyme at 480 nm established that the simple two-step mechanism found for copper- and iron-containing superoxide dismutases is not involved. At a low ratio (less than 15) of substrate concentration to enzyme concentration the decay of O2–is close to exponetial, whereas at much higher ratios (greater than 100) the observed decay is predominantly zero-order. The simplest interpretation of the results invokes a rapid one-electron oxidation-reduction cycle (‘the fast cycle’) and, concurrently, a slower reaction giving a form of the enzyme that is essentially unreactive towards O2– but which undergoes a first-order decay to yield fully active native enzyme (‘the slow cycle’). The fast cycle involves the native enzyme EA and a form of the enzyme EB which can be obtained also by treating the form EA with H2O2. Computer calculations made with such a simple model predict behaviour in excellent agreement with the observed results.

scholarly journals A pulse-radiolysis study of the manganese-containing superoxide dismutase from Bacillus stearothermophilus

1977 ◽  
Vol 165 (1) ◽  
pp. 81-87 ◽  
Author(s):  
M E McAdam ◽  
F Levelle ◽  
R A Fox ◽  
E M Fielden
Keyword(s):  
Superoxide Dismutase ◽  
Enzyme Activity ◽  
Substrate Concentration ◽  
Radical Anion ◽  
Pulse Radiolysis ◽  
Bacillus Stearothermophilus ◽  
Preceding Paper ◽  
Native Enzyme ◽  
Arrhenius Parameters ◽  
Mechanism Of Catalysis

In the preceding paper the mechanism of catalysis of the manganese-containing superoxide dismutase from Bacillus stearothermophilus was shown to involve a ‘fast cycle’ and a ‘slow cycle’ [McAdam, Fox, Lavelle & Fielden, 1977 (Biochem. J. 165, 71-79)]. Further properties of the enzyme was considered in the present paper. Pulse-radiolysis studies, under conditions of low substrate concentration to (i.e. when the fast cycle predominates), showed that enzyme activity decreases as pH increases (6.5-10.2). Activity was unaffected by the addition of H2O2 or NaN3 but slightly decreased by KCN. Both H2O2 and the reducing radical anion CO2– caused a decrease in A480 of the native enzyme. The rate of the fast catalytic cycle was independent of temperature (5-55 degrees C), and as temperature increases the slow cycle becomes relatively more important. Arrhenius parameters of the rate contants were estimated. The possible identity of the various forms of the enzyme is considered.

scholarly journals Studies of the limited degradation of mucus glycoproteins. The mechanism of the peroxide reaction

1985 ◽  
Vol 228 (3) ◽  
pp. 615-626 ◽  
Author(s):  
B Cooper ◽  
J M Creeth ◽  
A S Donald
Keyword(s):  
Superoxide Dismutase ◽  
Acetic Acid ◽  
Metal Ion ◽  
Histidine Residues ◽  
Essential Step ◽  
Oxidation Reduction ◽  
Reduction Cycle ◽  
Metal Ion Catalysis ◽  
Chelex Resin ◽  
Mucus Glycoproteins

The reaction between ovarian-cyst glycoproteins and H2O2 was investigated in the presence of a number of inhibitors and catalysts. Azide and 2H2O were separately found to have little effect, implying that singlet oxygen was not involved. Superoxide dismutase was destroyed by H2O2, but mannitol had no effect: thus generalized attack by OH., whether originating from HO2.- or more directly, is not indicated. The glycoproteins contained trace quantities of Cu and Fe, amounting to about 2 atoms of metal per glycoprotein molecule. Treatment of the glycoproteins with the strong chelator DETAPAC (diethylenetriaminepenta-acetic acid) or Chelex resin eliminated the reaction with H2O2; activity could be restored by addition of Cu2+ or Fe2+ in millimolar quantities. It was concluded that metal-ion catalysis is an essential step in the attack of H2O2 on glycoproteins. Spectroscopic and other evidence showed that Cu2+ (and probably Fe2+) complexes strongly with poly-L-histidine, and implies that the Cu2+ or Fe2+ in the glycoproteins is complexed with some of the histidine residues in the glycosylated backbone. Neither polyhistidine nor polyproline reacted with H2O2 in the absence of metal ions, but small quantities of Cu2+ or Fe3+ caused degradation. This was rapid with polyhistidine, which was converted largely into aspartic acid, but slower with polyproline, where limited conversion into glutamic acid occurs. These findings confirm the original hypothesis that peroxide attack on glycoproteins occurs largely at the histidine residues, with simultaneous peptidolysis. The mechanism most probably involves the liberation of OH. by an oxidation-reduction cycle involving, e.g. Cu+/Cu2+: specificity of attack at histidine is due to the location of the metal at these residues only.

Kinetics and mechanism of oxidation of DL-α-alanine by permanganate ion in acid perchlorate media

1991 ◽  
Vol 69 (12) ◽  
pp. 2018-2023 ◽  
Author(s):  
Refat M. Hassan
Keyword(s):  
Amino Acids ◽  
Ionic Strength ◽  
Acid Solution ◽  
Second Order ◽  
Perchloric Acid Solution ◽  
Oxidation Reduction ◽  
Initial Stage ◽  
Aqueous Perchloric Acid ◽  
Mechanism Of Oxidation ◽  
Kinetics Of

The kinetics of permanganate oxidation of DL-α-alanine in aqueous perchloric acid solution at a constant ionic strength of 2.0 mol dm−3 has been investigated spectrophotometrically. The reaction was found to show second-order kinetics overall with respect to each of the reactants in the slow initial stage; the second-order kinetics are not, however, maintained throughout the relatively fast final stage of reaction. The added salts lead to the prediction that Mn(III) and (or) Mn(IV) play a very important role in the reaction kinetics. A tentative mechanism consistent with the kinetics is discussed. Key words: kinetics, oxidation, reduction, amino acids, permanganate.

scholarly journals Kinetics of iron oxidation-reduction in hydrous silicic melts

2002 ◽  
Vol 87 (7) ◽  
pp. 829-837 ◽  
Author(s):  
Fabrice Gaillard ◽  
Bruno Scaillet ◽  
Michel Pichavant
Keyword(s):  
Iron Oxidation ◽  
Oxidation Reduction ◽  
Kinetics Of
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