Cytochrome oxidase oxygen binding

Wilson MT, Antonini G, Malatesta F, et al. 1994. Probing the oxygen binding site of cytochrome c oxidase by cyanide. J Biol Chem 269(39) 24114-24119. 

A). Cyanide ions (CN ) enter the organism in the form of hydrocyanic acid (HCN) the latter can be inhaled, released from cyanide salts in the acidic stomach juice, or enzymatically liberated from bitter almonds in the gastrointestinal tract The lethal dose of HCN can be as low as 50 mg. CN binds with high affinity to trivalent iron and thereby arrests utilization of oxygen via mitochondrial cytochrome oxidases of the respiratory chain An internal asphyxiation (histotoxic hypoxia) ensues while erythrocytes remain charged with O2 (venous blood colored bright red). 

Putidaredoxin. Cushman et al. (36) isolated a low molecular iron-sulfur protein from camphor-grown Pseudomonas putida. This protein, putidaredoxin, is similar to the plant type ferredoxins with two irons attached to two acid-labile sulfur atoms (37). It has a molecular weight of 12,000 and shows absorption maxima at 327, 425 and 455 nm. Putidaredoxin functions as an electron transfer component of a methylene hydroxylase system involved in camphor hydroxylation by P. putida. This enzyme system consists of putidaredoxin, flavoprotein and cytochrome P.cQ (38). The electron transport from flavoprotein to cytochrome P.cq is Smilar to that of the mammalian mixed-function oxidase, but requires NADH as a primary electron donor as shown in Fig. 4. In this bacterial mixed-function oxidase system, reduced putidaredoxin donates an electron to substrate-bound cytochrome P. g, and the reduced cytochrome P. g binds to molecular oxygen. One oxygen atom is then used for substrate oxidation, and the other one is reduced to water (39, 40). 

The reaction of 02 with cytochrome c oxidase to form the oxygenated species A (Fig. 18-11) is very rapid, occurring with apparent lifetime T (Eq. 9-5) of -8-10 is.139 Study of such rapid reactions has depended upon a flow-flash technique developed by Greenwood and Gibson.136/140/141 Fully reduced cytochrome oxidase is allowed to react with carbon monoxide, which binds to the iron in cytochrome a3 just as does 02. In fact, it was the spectroscopic observation that only half of the... 

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