Heme proteins catalase

This is accelerated by the iron heme protein catalase, a particularly efficient enzyme with one of the highest turnover numbers of all known enzymes (at 4x 107 molecules per second). This high rate reflects the important role for the enzyme, and its capacity for detoxifying hydrogen peroxide. 

Catalase is a heme protein belonging to the class of oxidoreductases with ferripro-toporphyrin-IX at the redox center, and it catalyzes the disproportionation of hydrogen peroxide into oxygen and water without the formation of free radicals. 

How does nature prevent the release of hydrogen peroxide during the cytochrome oxidase-mediated four-electron reduction of dioxygen It would appear that cytochrome oxidase behaves in the same manner as other heme proteins which utilize hydrogen peroxide, such as catalase and peroxidase (vide infra), in that once a ferric peroxide complex is formed the oxygen-oxygen bond is broken with the release of water and the formation of an oxo iron(IV) complex which is subsequently reduced to the ferrous aquo state (12). Indeed, this same sequence of events accounts for the means by which oxygen is activated by cytochromes P-450. 

Fig. 3.1 The molecular structure of heme b (also called protoporphyrin IX), the active center of myoglobin, hemoglobin, catalases, and peroxidases, among other heme proteins. 

The kinetics of reactions of NO with ferri- and ferro-heme proteins and models under ambient conditions have been studied by time-resolved spectroscopic techniques. Representative results are summarized in Table I (22-28). Equilibrium constants determined for the formation of nitrosyl complexes of met-myoglobin (metMb), ferri-cytochrome-c (Cyt111) and catalase (Cat) are in reasonable agreement when measured both by flash photolysis techniques (K= konlkQff) and by spectroscopic titration in aqueous media (22). Table I summarizes the several orders of magnitude range of kon and kQs values obtained for ferri- and ferro-heme proteins. Many k0f[ values were too small to determine by flash photolysis methods and were determined by other means. The small values of kQ result in very large equilibrium constants K for the... 

Craven, P. A., DeRuberts, F. R., and Pratt, D. W. (1979). Electron spin resonance study of the role of NO catalase in the activation of guanylate cyclase by NaN, and NH2OH. Modulation of enzyme responses by heme proteins and their nitrosyl derivatives.). Biol. Chem. 254, 8213-8222. 

As in myoglobin, hemoglobin (Fig. 7-23), and cytochrome c (see Fig 16-8), one axial coordination position on the iron of most heme proteins (customarily called the proximal position) is occupied by an imidazole group of a histidine side chain. However, in cytochrome P450 and chloroperoxidase a thiolate (-S ) group from a cysteinyl side chain, and in catalase a phenolate anion from a tyrosyl side chain, occupies the proximal position. The sixth or distal coordination position is occupied by the sulfur atom of methionine in cytochrome c and most other cytochromes with low-spin iron but cytochromes b5 and c3 have histidine. The high-spin heme proteins, such as cytochromes c, ... 

Metalloenzymes of at least three different types catalyze the destruction of superoxide radicals that arise from reactions of oxygen with heme proteins, reduced flavoproteins, and other metalloenzymes. These superoxide dismutases (SODs) convert superoxide anion radicals 02 into H202 and 02 (Eq. 16-26). The H202 can then be destroyed by catalase (Eq. 16-8). 

The mechanism of CPO-induced halogenation has been of interest since the discovery of this extraordinary set of heme proteins, which exhibit catalase, peroxidase, and cytochrome P450 activities in addition to biohalogenation (2159-2171). A general consensus mechanism has been proposed that does not involve free... 

Fascinated by the oxygen turnover processes catalyzed by heme proteins, namely the peroxidases, cytochromes P-450, and catalase, thousands of researchers appear be looking for active and robust metalloporphyrin catalysts. 

Halophilic proteins whose solution structures are currently under study include glyceraldehyde-3-phosphate dehydrogenase from Hal-oarcula vallismortis (Krishnan and Altekar, 1990) and a heme-binding catalase-peroxidase from H.marismortui (F. Cendrin, H. Jouvre, and G. Zaccai, private communication). 

How can a simple cofactor, such as heme, give rise to a wide spectrum of protein functionalities While the Fe(III)/Fe(II) couple has a standard redox potential of 0.77 V, when complexed with a protoporphyrin to form free heme, it may decrease to —0.115 V [3-5]. When heme is introduced into a protein matrix, redox potential shows an impressive variation of around 1 V. The electrochemical data for structurally characterized heme proteins involved in electron transfer and redox catalysis has been compiled at the Heme Protein Database (HPD, http //heme.chem. columbia.edu/heme) [6]. The database comprises not only peroxidases but also catalases, oxidases, monooxygenases, and cytochromes. From b-type heme with histidine-tyrosine ligation (E° = 0.55 V) to c-type heme with histidine-methionine... 

Suarez J, Ranguelova K, Jarzecki AA et al (2009) An oxyferrous heme/protein-based radical intermediate is catalytically competent in the catalase reaction of Mycobacterium tuberculosis catalase-peroxidase (KatG). J Biol Chem 284 7017-7029... 

Dioxygen Related Ligands Iron Heme Proteins Dioxygen Transport Storage Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases Iron Porphyrin Chemistry Long-range Electron Transfer in Biology. 

Myoglobin has the same prosthetic group as some peroxidases, such as horseradish peroxidase (HRP) or cytochrome c peroxidase, and reacts with H2O2 to produce a ferryl species, PFe(IV)=0, observed in the native peroxidase (see Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases). However, the catalytic activity of myoglobin toward substrate oxidation is very low, because... 

The b cytochromes contain noncovalently-attached protoheme in which the cysteine bridges are replaced by vinyl groups. The iron atom in most b cytochromes is ligated by two histidine nitrogen atoms, and has a redox potential of about 0 V. The 604 nm absorption band in reduced mitochondria is due to two a-type cytochromes, cyt a and cyt a, which are components of cytochrome oxidase (CcO) see Cytochrome Oxidase). A number of other classes of cytochromes have been discovered, including cytochrome peroxidases (CcP) (see Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases), cytochrome P-450, and cytochrome o see Iron Heme Proteins, Mono- Dioxygenases). 

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