Oxidation of ferrocytochrome c by mitochondrial cytochrome c oxidase.

Errede, Beverly; Haight, G. P.; Kamen, Martin D.

doi:10.1073/pnas.73.1.113

Cited by 64 publications

(30 citation statements)

References 14 publications

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“…When data were analyzed in a Lineweaver-Burk plot, two phases could be distinguished, each characterized by a K M and a k cat value resulting in a high and a low affinity phase as observed earlier (5, 20). The parameters for the high affinity phase are presented in Table II The K M can be taken as an apparent dissociation constant under certain conditions, and the work of several groups during the last few years has shown that K M is equivalent to K D for oxidase (21,22). We suppose from our earlier investigations that this holds at least for the condition of I ϭ 56 mM (6).…”

Section: Resultsmentioning

confidence: 91%

Tryptophan 121 of Subunit II Is the Electron Entry Site to Cytochrome-c Oxidase in Paracoccus denitrificans

Witt¹,

Malatesta²,

Nicoletti³

et al. 1998

Journal of Biological Chemistry

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To investigate the contribution of hydrophobic residues to the molecular recognition of cytochrome c with cytochrome oxidase, we mutated several hydrophobic amino acids exposed on subunit II of the Paracoccus denitrificans oxidase. K M and k cat values and the bimolecular rate constant were determined under steady-or presteady-state conditions, respectively. We present evidence that Trp-121 which is surrounded by a hydrophobic patch is the electron entry site to oxidase. Mutations in this cluster do not affect the binding of cytochrome c as the K M remains largely unchanged. Rather, the k cat is reduced, proposing that these hydrophobic residues are required for a fine tuning of the redox partners in the initial collisional complex to obtain a configuration optimal for electron transfer.Electron transfer between redox proteins has been under extensive investigation during the last years. The protein surfaces involved in complex formation have been of particular interest as it became clear that electron transfer depends on specific recognition with an affinity low enough to allow rapid dissociation. Several studies with cytochrome c and its different redox partners demonstrated the involvement of electrostatic interactions mediated by lysines surrounding the heme edge on cytochrome c and acidic residues on the counterpart (1-6). Nevertheless, it became obvious from ionic strength dependence measurements that electrostatic interactions are not the only criterion governing optimal electron transfer (2). The bell-shaped dependence of activity on ionic strength lead to the proposal that at low ionic strength the redox partners lack the conformational flexibility to achieve a configuration optimal for electron transfer (7,8) besides the fact that product dissociation becomes rate-limiting. At high ionic strength the rate of non-productive collisions increases due to the shielding of charges. Around the ionic strength optimum, when long range electrostatic forces have roughly aligned the reacting proteins, configurational freedom still prevails for short range forces such as hydrophobic interaction to contribute significantly to a configuration optimal for electron transfer.Cytochrome-c oxidase (cytochrome aa 3 ; EC 1.9.3.1) (for reviews see Refs. 9 -11) is one of the terminal enzymes in the respiratory chain of Paracoccus denitrificans besides a quinol oxidase (cytochrome ba 3 (12)) and an alternative cytochrome oxidase (cytochrome cbb 3 (11)). The three main subunits of cytochrome aa 3 show significant homology to the mitochondrially encoded subunits of the eukaryotic cytochrome oxidase. Heme a and the binuclear center (heme a 3 ⅐Cu B ) are located in subunit I, whereas the Cu A center which is the primary electron acceptor resides in subunit II. As stated above, the involvement of electrostatic interactions in the reaction between cytochrome c and cytochrome-c oxidase mediated by acidic residues predominantly located on subunit II of the P. denitrificans oxidase has already been demonstrated (6).To investigate the c...

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Section: Resultsmentioning

confidence: 91%

Tryptophan 121 of Subunit II Is the Electron Entry Site to Cytochrome-c Oxidase in Paracoccus denitrificans

Witt¹,

Malatesta²,

Nicoletti³

et al. 1998

Journal of Biological Chemistry

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“…1 also shows that cytochrome c, equimolar to the oxidase, is very effective in protecting the enzyme from carbodiimide modification and inhibition particularly with CMC. It is noteworthy that under these conditions only the high affinity cytochrome c binding site is occupied [20,21]. Higher temperatures increase the rate of reaction without changing the inhibition patterns and the extent of cytochrome c protection (see below).…”

Section: Resultsmentioning

confidence: 99%

“…Similar patterns were found at higher temperatures except for a greater efficiency of cross-linking in the presence of CMC with respect to EDC (not shown). On the base of kinetic studies it has been suggested that more than one binding site for cytochrome c exist on isolated cytochrome c oxidase [20,21]. Only the so-called 'high affinity binding site' is involved in these experiments.…”

Section: Resultsmentioning

confidence: 99%

Different polypeptides of bovine heart cytochrome c oxidase are in contact with cytochrome c

Bisson¹,

Montecucco²

1982

FEBS Letters

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Two water‐soluble carbodiimides, differing in molecular dimensions, have been used to characterize the cytochrome c binding site of bovine heart cytochrome c oxidase. Several polypeptide components of the enzyme contain acidic residues which are modified by these reagents. Carboxyl groups present in subunit II, VII and polypeptide c, are protected from modification when cytochrome c, equimolar to oxidase, is added and they can cross‐link to the substrate once activated by the carbodiimide. Comparison of the modification patterns suggest that the most reactive residues are located on subunit II and VII, the former being also more exposed. The data obtained indicate that eventhough subunit II plays the major role in binding cytochrome c, at least two other lower M r polypeptides contribute to the cytochrome c binding domain.

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“…Errede et al 10 have published a detailed study of CCO kinetics, with an analysis of the results in light of several proposed mechanisms. The deduced rate equation for the reaction is complex, and includes many parameters relating to various steps in the proposed mechanism.…”

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confidence: 99%