Condensation of dichlorodimethylsilane in silent discharges

Andreev, D. N.

doi:10.1007/bf00942893

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“…The values obtained for Km (17.5 and 12.4 mM evaluated from the 418and 428-nm data, respectively) are in good agreement with previously reported values, e.g., 5 -10 mM at pH 7.4 with Tween 80 as the solubilizing detergent (Van Buuren et al, 1972;Andreev & Konstantinov, 1983). Our values for the apparent second-order rate constant of the fast k' reaction also agree with the average value of 2.5 M-1 s-1 that Naqui et al (1984) obtained for seven different preparations of oxidase (evaluated at pH = 7.4 in 0.1 M phosphate buffer at 21 °C).…”

Section: Discussionsupporting

confidence: 91%

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Kinetics and mechanism for the binding of HCN to cytochrome c oxidase

Panda¹,

Robinson²

1995

Biochemistry

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The kinetics of cyanide binding to cytochrome c oxidase were systematically studied as a function of [HCN], [oxidase], pH, ionic strength, temperature, type and concentration of solubilizing detergent, and monomer-dimer content of oxidase. On the basis of these results a minimum reaction mechanism is proposed in which the spectrally visible rapid and slow cyanide binding reactions are two consecutive first-order reactions, not parallel reactions with different conformers of cytochrome c oxidase. The fast reaction (k'obs) follows saturation type kinetics to form an HCN complex that subsequently undergoes a slow reaction (k'obs). The fast k'obs reaction is independent of ionic strength but is strongly dependent upon pH. Two pK values were evaluated from the bell-shaped rate versus pH profile; one is due to an ionizable group on the protein (pKa = 7.45), while the other is that of HCN (pKHCN = 9.15). Therefore, oxidase is reactive toward HCN only when the group on the protein is unprotonated. The slow k'obs reaction is not a reaction of oxidase with either CN- or HCN; in fact, the product formed by the fast k'obs reaction, the oxidase-HCN complex, still undergoes the slow k" process even if all of the excess KCN is removed. The apparent rate constant of the slower phase (k"obs) is independent of all the variations done in this study, and it probably corresponds to either a slow conformational change in the protein or a change in ligand coordination at one of the metal centers after HCN binds to the bimetallic center of oxidase. Based upon the bell-shaped pH dependence of the fast phase and the pH independence of the slow phase, the mechanism also predicts that a single conformer of cytochrome c oxidase can exhibit either monophasic or biphasic cyanide binding kinetics depending upon the pH. At either very low or very high pH, the two rates become comparable in magnitude, which makes the reaction appear to be monophasic even though both reactions still occur. The amount of monomeric or dimeric oxidase only slightly affects the magnitude of k'obs and k"obs values, and both processes are clearly present in both types of oxidase.

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Section: Discussionsupporting

confidence: 91%

“…[KCN] dependence of the reaction at only a single pH (Van Buuren et al, 1972a,b;Mus ato v & Konstantinov, 1988; Andreev & Konstantinov, 1983). These values should not be interpreted as intrinsic constants until a complete study of all factors that influence the kinetics is performed (Malmstrom, 1990a,b).…”

mentioning

confidence: 99%

Kinetics and mechanism for the binding of HCN to cytochrome c oxidase

Panda¹,

Robinson²

1995

Biochemistry

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show abstract

Condensation of dichlorodimethylsilane in silent discharges

Cited by 1 publication

References 4 publications

Kinetics and mechanism for the binding of HCN to cytochrome c oxidase

Kinetics and mechanism for the binding of HCN to cytochrome c oxidase

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