In cytochrome

Figure C3.2.5. Strongest tunnelling patliways between surface histidines and tire iron atom in cytochrome c. Steps in patliways are denoted by solid lines (covalent bonds), dashed lines (hydrogen bonds), and tlirough-space contacts (dotted lines). Electron transfer distance to His 72 is 5 A shorter tlian in His 66, yet tire two rates are approximately...

Hofacker, I., Schulten, K. Oxygen and proton pathways in cytochrome-c oxidase. Proteins Str. Funct. Genet. 29 (1998) 100-107... 

Fig. 4. The cycle of events involved in cytochrome (Cyt) P q (Cyt P450 Fe + ) mediated dmg metaboHsm where NADP is nicotinamide disphosphate and...

In cytochrome bs62 (a) adjacent helices are antiparallel, whereas the human growth hormone (b) has two pairs of parallel a helices joined in an antiparallel fashion. 

The Rieske clusters observed in cytochrome be complexes from traditional sources (i.e., mitochondria, proteobacteria, plastids, and cy-... 

Studies (see, e.g., (101)) indicate that photosynthesis originated after the development of respiratory electron transfer pathways (99, 143). The photosynthetic reaction center, in this scenario, would have been created in order to enhance the efficiency of the already existing electron transport chains, that is, by adding a light-driven cycle around the cytochrome be complex. The Rieske protein as the key subunit in cytochrome be complexes would in this picture have contributed the first iron-sulfur center involved in photosynthetic mechanisms (since on the basis of the present data, it seems likely to us that the first photosynthetic RC resembled RCII, i.e., was devoid of iron—sulfur clusters). 

Narhi LO, AJ Fulco (1987) Identification and characterization of two functional domains in cytochrome P-450g, j.3, a catalytically self-sufficient monooxygenase induced by barbiturates in Bacillus megaterium. J Biol Chem 262 6683-6690. 

Harder PA, DP O Keefe, JA Romesser, KJ Leto, CA Omer (1991) Isolation and characterization of Strepto-myces griseolus deletion mutants affected in cytochrome P-450-mediated herbicide metabolism. Mol Gen Genet 227 238-244. 

Only three steps of the proposed mechanism (Fig. 18.20) could not be carried out individually under stoichiometric conditions. At pH 7 and the potential-dependent part of the catalytic wave (>150 mV vs. NHE), the —30 mV/pH dependence of the turnover frequency was observed for both Ee/Cu and Cu-free (Fe-only) forms of catalysts 2, and therefore it requires two reversible electron transfer steps prior to the turnover-determining step (TDS) and one proton transfer step either prior to the TDS or as the TDS. Under these conditions, the resting state of the catalyst was determined to be ferric-aqua/Cu which was in a rapid equilibrium with the fully reduced ferrous-aqua/Cu form (the Fe - and potentials were measured to be within < 20 mV of each other, as they are in cytochrome c oxidase, resulting in a two-electron redox equilibrium). This first redox equilibrium is biased toward the catalytically inactive fully oxidized state at potentials >0.1 V, and therefore it controls the molar fraction of the catalytically active metalloporphyrin. The fully reduced ferrous-aqua/Cu form is also in a rapid equilibrium with the catalytically active 5-coordinate ferrous porphyrin. As a result of these two equilibria, at 150 mV (vs. NHE), only <0.1%... 

Mills DA, Florens L, Hiser C, Qian J, Ferguson-Miller S. 2000. Where is outside in cytochrome c oxidase and how and when do protons get there Biochimica et Biophysica Acta, Bioenergetics 1458, 180-187. 

Nicholls P, Peterson LC, Miller M, et al. 1976. Ligand-induced spectral changes in cytochrome c oxidase and their possible significance. Biochim Boughs 449 188-196. 

In cytochrome-c [PtCU]2- binds to methionine 65 on the outside of the protein (64). Again the chloride is probably displaced as the reagent is applied in phosphate buffer. Dickerson and co-workers consider that the platinum is oxidized to a Pt(IV) complex but this seems unlikely as it does not occur in the reaction of [PtClJ2- with simple amino-acids. 

Oya, H., Costello, L.C. and Smith, W.N. (1963) The comparative biochemistry of developing Ascaris eggs. II. Changes in cytochrome c oxidase activity during embryonation. Journal for Cellular and Comparative Physiology 62, 287—294. 

Figure 2.6 Chemical structures (a) and axial ligands (b) to the haem groups in cytochromes a, b and c. From Voet and Voet, 1995. Reproduced by permission of John Wiley Sons, Inc.

---