Catalase cyanide complex

The inhibition of catalase by cyanide shows none of the characteristics of the azide or hydroxylamine inhibition as is to be expected if cyanide combines with the ferric form. At low peroxide concentrations about 10-3 M the equilibrium constant for the formation of the cyan-catalase complex (Ki) determined from kinetic data using the expression... 

Table V summarizes some of the classic measurements of magnetic susceptibility on heme compounds. The compounds fall into two classes high spin (H 0) and low spin (CN, Os), in agreement with the measurements on simpler complexes mentioned above in the discussion on ligand field theory. The hydroxide complex of heme 195) with hemoglobin has been shown to exist in at least two forms. The catalase complexes are peculiar in that an intermediate magnetic moment is foimd even for the cyanide complex. The ease of oxidation of the heme in this compound may account for part of this aberancy. Another possibility is the assumption of a peculiar (or absent) fifth ligand.

Thiosulfate cyanide sulfurtransferase symmetry in 78 TTiiouridine 234 Three-dimensional structures of aconitase 689 adenylate kinase 655 aldehyde oxido-reductase 891 D-amino acid oxidase 791 a-amylase, pancreatic 607 aspartate aminotransferase 57,135 catalytic intermediates 752 aspartate carbamyltransferase 348 aspartate chemoreceptor 562 bacteriophage P22 66 cadherin 408 calmodulin 317 carbonic acid anhydrase I 679 carboxypeptidase A 64 catalase 853 cholera toxin 333, 546 chymotrypsin 611 citrate synthase 702, 703 cutinase 134 cyclosporin 488 cytochrome c 847 cytochrome c peroxidase 849 dihydrofolate reductase 807 DNA 214, 223,228,229, 241 DNA complex... 

The bacterium Lactobacillus plantarum and its closest allies are unusual in that they are aerobic organisms but do not produce a superoxide dismutase. This bacterium instead accumulates Mn(II) to an intramolecular level on the order of 25 mM (150-152). In vitro studies indicated that Mn(II) formed a complex with lactate which possessed significant superoxide activity (153). These bacteria are additionally unable to produce heme and, consequently, when grown in the absence of heme, produce a hemeless catalase, or pseudocatalase (154-158). Unlike heme-containing catalases, the enzyme is not inhibited by cyanide or azide, and the addition of either Mn or Fe into the growth medium increased the amount of the pseudocatalase present. However, neither of the metals could be detected in partially purified enzyme assays (157). 

Catalase reacts reversibly with some weak acids forming spectroscopically and magnetically distinct noncovalent derivatives. Of these, catalase-cyanide, -azide, -fluoride, -formate, and -acetate complexes have been extensively studied (37, 135, 136) and reviewed in some detail (16-18). Briefly, there is a consensus that such reactions do not involve heme-heme interaction and, with the possible exception of carboxylate ligands (102), all presumably result in replacement of the proximal aquo ligand at Ls in a stoichiometric reaction shown in Eq. (11) ... 

Thus, Brill and Sandberg pointed out that whenever imidazole is coordinated to the ferriprotoporphyrin (H, 79, 82) the difference spectra of low-spin vs. high-spin complexes are characterized by an absorption band below 250 nm (A 236-23s approximately 6-12 X 10 M cm" ). Such a diagnostic band, attributable to charge transfer transitions from L5 to porphyrin orbitals, was noted in the difference spectrum of ferricata-lase cyanide (low spin) vs. catalase (high spin) 74), thereby favoring L5 = His. 

Inhibition of Catalase Activity of Azide, Hydroxylamine, and Cyanide, the Relative Affinity of These Substances for the Enzyme and the Corresponding Dissociation Constants for the Complexes... 

The noncompetitive inhibition of the decomposition of hydrogen peroxide by cyanide is not immediately obvious from the above reaction mechanism for if cyanide can compete in the formation of the peroxide complex which is responsible for the oxygen evolution in step IV, competitive inhibition might be expected. However, under the experimental conditions necessary to observe peroxide decomposition, an excess of peroxide is required and this is sufficient to give the maximal concentration of the peroxide complex, 1.2 or 1.6 moles of bound peroxide for each erythrocyte or bacterial catalase molecule respectively, i.e., the peroxide complex concentration is independent of the peroxide concentration. Analysis of the system under these conditions shows noncompetitive inhibition to hold. 

In a more general context of hemoproteins some further studies appear worth mentioning. A coral allene oxide synthase has been characterized which employs a heme in the conversion of 8R-hydroperoxyeicosatetraenoic acid into the corresponding allene oxide. EPR of the ferric enzyme and its cyanide and azide complexes strongly suggested tyrosinate ligation, as in catalase, but the access of small molecules to the heme as well as the interaction with the protein environ-... 

Reactions of hemoglobin with cyanide and the magnetic properties of the cyanide complex. Equilibrium constant of the reaction. Reaction of cyanide with catalase and peroxidase. Magnetic properties of products. Reaction of hemoglobin with fluoride and its relation to the reaction with hydroxyl ion. Equilibrium constants for reactions of fluoride with cytochrome c, catalase, and peroxidase. Magnetic effects associated with these reactions. Velocity of reaction of ferrihemoglobin with hydro-sulfide. Magnetic properties of product. Reactions with azide. Reactions of hydroxyl ion with various heme proteins. Reconsideration of all the results in connection with possibility of interactions between hemes. 

Horse liver catalase, containing four iron atoms but supposedly only three unmodified hemes, unites with three cyanide ions. In this molecule the susceptibility of a single heme-cyanide complex is estimated as about 4000 X 10" cc. n = 3.1), which is interpreted to indicate covalent bonding, though it is higher than would be expected for this. 

At 4° C. peroxidase has little oxidase activity in the absence of Mn++, so that the influence of several variables can be studied easily. Catalase and cyanide are inhibitory, carbonmonoxide is not. Therefore it is reasonable to suppose that ferroperoxidase is not involved. Peroxidase should be present under the form of complex 2. The possible structures of the different complexes are shown in Table VIII. 

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