The pre-steady state reaction of ferrocytochrome c with the cytochrome c-cytochrome aa3 complex

Veerman, E.C.I.; Wilms, J.; Casteleijn, G.; Gelder, B.F. Van

doi:10.1016/0005-2728(80)90151-6

Cited by 43 publications

(14 citation statements)

References 17 publications

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“…Several studies have concluded that the rate constant for the dissociation of the high-affinity cytochrome c-cytochrome oxidase complex is small under low-ionic-strength conditions (<25 mM), with values ranging from 2 to 10 s-1 (24,25). The reaction of a second molecule of cytochrome c with the high-affinity cytochrome c-cytochrome oxidase complex is much faster under most conditions than the rate of dissociation of this complex, consistent with the proposed existence of a second catalytic site for cytochrome c on the enzyme (23).…”

supporting

confidence: 63%

“…As previously mentioned, the rate-limiting step, under low-ionic-strength conditions, in the steady-state oxidation of ferrocytochrome c by cytochrome oxidase is the rate of dissociation of the ferricytochrome c-cytochrome oxidase complex (24,25). The most definitive evidence in this regard is that the presteadystate reaction of purified ferrocytochrome cl with the ferricytochrome c-cytochrome oxidase complex is first order, yielding a rate constant of 2.5 s-1 in 5 mM phosphate (pH 7.0) (25), which is at least 2 orders of magnitude slower than the pseudo-first-order rate constant for the reaction of purified ferrocytochrome cl with ferricytochrome c under the same conditions (23 and also an increase in the turnover rate, constituting a lower-affinity kinetic phase, unless the decrease in binding affinity is so large as to lead to an overwhelming decrease in the concentration of the enzyme-substrate complex.…”

mentioning

confidence: 99%

“…That a second molecule of cytochrome c can react with the high-affinity cytochrome c-cytochrome oxidase complex has been further substantiated by analysis of the presteady-state kinetics (23). The time course of the rapid kinetic oxidation of ferrocytochrome c by purified cytochrome oxidase does not fit a single exponential when cytochrome c is in slight excess.…”

mentioning

confidence: 99%

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Single catalytic site model for the oxidation of ferrocytochrome c by mitochondrial cytochrome c oxidase.

Speck¹,

Dye²,

Margoliash³

1984

Proc. Natl. Acad. Sci. U.S.A.

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A single catalytic site model is proposed to account for the multiphasic kinetics of oxidation of ferrocytochrome c by cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1). This model involves nonproductive binding of substrate .to sites near the catalytic site on cytochrome c oxidase for cytochrome c, decreasing the binding constant for cytochrome c at the catalytic site. This substrate inhibition results in an increase.in the first-order rate constant for the dissociation of the ferricytochrome c-cytochrome c oxidase complex, the rate-limiting step in the steady-state turnover of electrons between cytochrome c and cytochrome c oxidase in the spectrophotometric assay, yielding increases in the initial rate as well as the Michaelis constant-namely, multiple kinetic phases. (2) and Borei (3) proposed that the reaction involved the formation of an enzyme-substrate complex. In 1949, Slater (4) confirmed and extended the observations of these authors, demonstrating that at any single concentration of enzyme [provided in the form of a KeilinHartree heart muscle particle preparation (5)], the kinetics indeed fit the Michaelis-Menten relation. However, the oxidation of ferrocytochrome c monitored spectrophotometrically (namely, in the absence of any added reducing agent) was generally observed to follow a first-order time course (6-13). Because the observed first-order rate constants decrease with increasing cytochrome c concentration rather than remaining unchanged, as one would expect for a simple bimolecular collisional mechanism with no precursor-pair formation, Smith and Conrad (13) suggested that the hyperbolic dependence of the initial velocity on cytochrome c concentration was due to inhibition of the reaction by cytochrome c itself.That this was not the only possible explanation of these kinetics followed from Minnaert's (14) elegant analysis, in which it was shown that a first-order time course could arise from equal binding of ferro-and ferricytochromes c to cytochrome oxidase, with ferrocytochrome c forming a productive complex while ferricytochrome c acted as a competitive inhibitor. This hypothesis was supported by Yonetani and Ray (15), who demonstrated that (i) under conditions in which first-order kinetics are observed, the K1 for ferricytochrome c is the same as the apparent Michaelis constant for ferrocytochrome c and (ii) at more alkaline pH values, where the kinetics deviate from a first-order time course, the K1 for ferricytochrome c is no longer equal to the apparent Km for the reaction.Indeed, inspection of the Michaelis-Menten equation, which takes into account binding of product to the enzyme, leads to the expression: dp _ Vmax 15= kobS, dt LKm + (s + P)when Km is a good approximation of Ks, the equilibrium substrate binding constant, and the binding of substrate and product are equivalent, namely K, = Kp (16). Thus, kobs is a first-order rate constant that is distinguishable from an ordinary first-order rate constant because it is a function of s + p, the tot...

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supporting

confidence: 63%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Single catalytic site model for the oxidation of ferrocytochrome c by mitochondrial cytochrome c oxidase.

Speck¹,

Dye²,

Margoliash³

1984

Proc. Natl. Acad. Sci. U.S.A.

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“…[cyt c2 'I. Therefore, the apparent second-order rate constant determined in our experiments will, for this combination, decrease from k l , which is the actual second-order rate constant normally observed [20], to…”

Section: Purification Of Native Human Cytochrome C Oxidasementioning

confidence: 52%

“…At low ionic strength ( I = 18 mM), a fast reduction of heme a was observed for the presteady-state reaction between horse cytochrome c and human cytochrome c oxidase, although still considerably slower than the reaction of the human oxidase with its own cytochrome c. The observed reduction of heme a most probably reflects the 'low-affinity' reaction of a second molecule of cytochrome c with the 1 : 1 cytochrome c/cytochrome-c-oxidase complex [20]. Our results showed this 'low-affinity' reaction to be little affected by the absence of the proper conformations in the 'high-affinity' complex of horse cytochrome c with human cytochrome c oxidase.…”

Section: Purification Of Native Human Cytochrome C Oxidasementioning

confidence: 90%

Presteady‐state and steady‐state kinetic properties of human cytochrome c oxidase

Kuilenburg

Gorren²,

Dekker

et al. 1992

European Journal of Biochemistry

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Human cytochrome c oxidase was purified in a fully active form from heart and skeletal muscle. The enzyme was selectively solubilised with octylglucoside and KCl from submitochondrial particles followed by ammonium sulphate fractionation. The presteady‐state and steady‐state kinetic properties of the human cytochrome c oxidase preparations with either human cytochrome c or horse cytochrome c were studied spectrophotometrically and compared with those of bovine heart cytochrome c oxidase. The interaction between human cytochrome c and human cytochrome c oxidase proved to be highly specific. It is proposed that for efficient electron transfer to occur, a conformational change in the complex is required, thereby shifting the initially unfavourable redox equilibrium. The very slow presteady‐state reaction between human cytochrome c oxidase and horse cytochrome c suggests that, in this case, the conformational change does not occur. The proposed model was also used to explain the steady‐state kinetic parameters under various conditions. At high ionic strength (I= 200 mM, pH 7.4), the kcat was highly dependent on the type of oxidase and it is proposed that the internal electron transfer is the rate‐limiting step. The kcat value of the ‘high‐affinity’ phase, observed at low ionic strength (I= 18 mM, pH 7.4), was determined by the cytochrome c/cytochrome c oxidase combination applied, whereas the Km was highly dependent only on the type of cytochrome c used. Our results suggest that, depending on the cytochrome c/cytochrome c oxidase combination, either the dissociation of ferricytochrome c or the internal electron transfer is the rate‐limiting step in the ‘high‐affinity’ phase at low ionic strength. The ‘low‐affinity’kcat value was not only determined by the type of oxidase used, but also by the type of cytochrome c. It is proposed that the internal electron‐transfer rate of the ‘low‐affinity’ reaction is enhanced by the binding of a second molecule of cytochrome c.

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Cytochrome c Function

Margoliash¹

1982

Electron Transport and Oxygen Utilization

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The pre-steady state reaction of ferrocytochrome c with the cytochrome c-cytochrome aa3 complex

Cited by 43 publications

References 17 publications

Single catalytic site model for the oxidation of ferrocytochrome c by mitochondrial cytochrome c oxidase.

Single catalytic site model for the oxidation of ferrocytochrome c by mitochondrial cytochrome c oxidase.

Presteady‐state and steady‐state kinetic properties of human cytochrome c oxidase

Cytochrome c Function

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