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PubMed1978

[Kinetics and mechanism of nucleophilic effect on the oxidation of o-dianisidine catalyzed by horseradish peroxidase].

The effects of benzimidazole and 4-nitroimidazole on the reaction of o-dianisidine peroxidase oxidation within the pH range of 3.7--9.0 were studied. Both substituted imidazoles activate the reaction at less than 0.6. In the presence of 4-nitroimidazole the activation is non-competitive, whereas in the presence of benzimidazole it is of a mixed type, which is close to the non-competitive one. The kinetic parameters (kAcat, alpha, KA) for the reaction activated by both imidazoles were determined. It was assumed that the activators interact with the protein group (pK approximately to 6.5), which limits the enzyme activity. This results in the increase of pKapp of the protein group in question, resulting in the appearance of the maximal peroxidase activity in the alkaline region of pH. It was shown that the intermolecular interactions involved in the peroxidase-induced oxidative catalysis are largely due to electrostatic rather than to hydrophobic factors.

Benzidines↗
PubMed1978

Acid and alkaline forms of the higher oxidation state of kangaroo, horse, and sperm whale myoglobin.

Myoglobin(IV), the derivative of myoglobin at the formal oxidation state IV, prepared from kangaroo (Megaleia rufa), horse, or sperm whale myoglobin, when cooled to liquid nitrogen temperature, assumes acid and alkaline forms with different optical spectra. The essential features of the optical spectra of the acid forms are the same as those of leghemoglobin(IV) and are very similar to those of optical spectra of the red higher oxidation states of catalases and peroxidases. This shows that the configuration of the heme iron is the same throughout these compounds. That configuration is believed to be Fe(IV) in a porphyrin environment. The optical spectra of alkaline mammalian myoglobin(IV), like that of alkaline leghemoglobin(IV), resemble those of the alkaline low spin ferric proteins. Kangaroo myoglobin(IV) may be prepared by reaction of ferrous myoglobin with hydrogen peroxide. The acid forms of myoglobin(IV) are conveniently prepared by cooling solutions in borate buffers, initially pH 8.3, to liquid nitrogen temperature. At this temperature borate buffers become acidic.

Animals↗
PubMed1978

Resonance Raman studies on the ligand-iron interactions in hemoproteins and metallo-porphyrins.

The resonance Raman spectra (RRS) were measured for various hemoproteins, as well as for free hemes, and analysed in terms of the interactions between the porphyrin ring and the heme iron and between the axial ligand and the heme iron. To establish vibrational assignments, the RRS of metallo-octae-thylporphyrin (M(OEP)), its 15N substituted and meso-deuterated derivatives were measured. It was found that the Raman line corresponding to the oxidation state marker of hemoproteins involves appreciable displacement of the pyrrolic nitrogen atoms toward metal ion but not that of methine bridges and that the frequencies of methine-bridge CC stretching vibrations are altered by the conjugation interaction between the porphyrin ring and the metal ion present. The prominent Raman lines of Ni(OEP) were assigned on the basis of the normal coordinate analysis. The Raman spectra of heme a bis-imidazole complex (Fe(A)(Im)2) in the presence of cyanide changed when pH was reduced to neutral. It implied formation of cyanhydrin at the peripheral formyl group of heme a. The Fe(A)(Im)2 formed an addition compound with NaHSO3 in a neutral solution but the added NaHSO3 was eliminated when the heme iron was reduced. The Raman spectra of hemoproteins were classified into four groups on the basis of the relative intensities and frequencies of the four key bands. It demonstrated the existence of two kinds of ferrous low-spin states. The difference between the two species was attributed to the difference in the nature of chemical bond between the heme iron and its sixth ligand (L). The Fe-L bonds of ferrous low-spin molecules in Groups A and C are mainly associated with the dz2(Fe)-lone pair and dz(Fe)-II(L) interactions, respectively. This interpretation of the Raman spectra appears consistent with the experimental facts that the ferrous low-spin molecules in Group C photodissociate upon illumination of light at the Soret band and also that the internal stretching frequencies of the sixth ligand are shifted to lower frequency upon coordination to the heme iron. The frequency of the oxidation state marker of reduced cytochrome P-450 (P-450cam) was unusually low in comparison with those of other hemoproteins. It was ascribed to delocalization of electrons from the thiolate anion to the porphyrin II*(ring) orbital through the pi-type molecular orbital (Eq.3). The RRS of reduced P-450cam.metyrapone adduct was quite close to that of reduced cytochrome b5. In conclusion, the Raman frequencies of hemoproteins may depend primarily upon the amount of electrons delocalized to the II* orbital of the porphyrin ring. The coordination of lone-pair electrons of the axial ligand to the iron dz2 orbital yields bond energy but scarcely affects the Raman frequencies. If the pi orbital of the axial ligand interacts with the iron dpi orbital, it perturbs the delocalization of the dpi(Fe) electrons to the II*(ring) orbital of porphyrin ring and thus affects the Raman frequencies.

Chemical Phenomena↗
PubMed1978

Analysis of acid-base properties of peroxidase and myoglobin.

Two heme-linked groups of horseradish peroxidases, characterized by pKa = 5.8 (isoenzyme A) and 7.3 (isoenzyme C), are believed to be distal amino acid residues and, judging by their acid-base properties in various derivatives, influence the functions of these isoenzymes. In contrast, in myoglobin ionization of the distal histidine does not influence its reactivity. Accordingly, we conclude that the interaction of the distal base with a 6th ligand is weak in myoglobin but very strong in peroxidases.

Hemoglobins↗
PubMedDate not supplied

Factors affecting in vitro lipid peroxidation of rat brain homogenate.

Peroxidation of the unsaturated lipid of tissue homogenates is an established method to assess the antioxidant or vitamin E status of animals. In the present study the spontaneous lipid peroxidation in air of rat brain homogenates is reported. The effects of various factors like pH, time, concentration of tissues, temperature, ferrocompounds and catalysis by added tissues like liver are described. Rat brain homogenates appear to be a suitable preparation for in vitro studies of lipid peroxidation.

Animals↗
PubMedDate not supplied

[Photoinduced reduction of NAD(P) in the cells of green sulfur bacteria].

The spectrum of a photoinduced increase in luminescence of the cells of the gree sulphur bacterium Chlorobium limicola f. thiosulfatophilum, within the range of 400 to 520 nm, was found to correspond to the spectrum of luminescence of NADH in the protein-bound form. Photoinduced reduction of NAD(P) in green bacteria, contrary to purple bacteria, is not susceptible to the action of p-chlorocarbonylcyanide phenlhydrazone which uncouples photophosphorylation. Therefore, in Chlorobium limicola f. thiosulfatophilum, NAD(P) is reduced by direct non-cyclic transport of electrons via the photosynthetic chain. NAD(P)H is utilized mainly in the system of CO2 fixation; the process is inhibited by fluoroacetate, and the inhibition is eliminated by substrates of the cycle of carboxylic acids.

Carbon Dioxide↗
PubMed1976

Dependence of starch synthase activity from maize leaves on light, pH and redox state.

The starch synthase activity of bundle sheath cells of maize leaves is very low in darkened plants and increases on illumination. In order to find an explanation of these facts we subjected leaf strips, isolated bundle sheath cells and enzymic preparations to pH-changes and to oxidizing or reducing substances. We found that the increase of the activity produced by light could also be caused in the leaf strips by adding malate to the suspending fluid in the dark. On the contrary, with isolated bundle sheath cells no increase with light or with the addition of malate could be observed. There was a decrease of activity due to acidification or to the addition of dichlorophenol-indophenol (DCPIP). The same effect could be observed with enzymic preparations as with the isolated bundle sheath cells, whereas the decrease of activity was higher by acidification of samples coming from darkened plants than for those enzymes prepared from illuminated plants. Also other substances inhibited the synthase activity: benzoquinone, DOPA, caffeic acid, TMPD or Fe (CN6) 3- and PCMB, while only DTE could increase it. After preincubation with PCMB the enzyme activity could be restored with DTE, not so for the preincubation with DCPIP. With an enzymic preparation that contained intact organelles the increase of activity could also be produced by NADH. Thus we follow that the decrease of synthase activity in the darkened plants is due to acidification and to the presence of oxidizing substances, too.

Glucosyltransferases↗
PubMedDate not supplied

Reductive metabolism of nitrofurantoin in the rat.

The reductive metabolism of nitrofurantoin under anaerobic conditions was characterized in various tissues from control, germ-free, and germ-free acclimatized rats. Nitrofurantoin metabolism was highest in homogenates of cecum and colon contents of germ-free acclimatized and control rats, but was absent from those of germ-free animals. Appreciable levels of activity were also present in homogenates of liver and of small intestine walls with lesser rates of metabolism observed in kidney homogenates. The major metabolite of nitrofurantoin, which was isolated and purified by high-pressure liquid chromatography, was identified as 1-[[(3-cyano-1-oxopropyl)-methylene]amino]-2,4-imidazolidinedione. A second, minor metabolite with high-pressure liquid chromatography and ultraviolet absorption characteristics similar to those of 1-[[(5-amino-2-furanyl)methylene]amino]-2,4-imidazolidinedione (aminofurantoin) was detected in cecum and colon contents.

Anaerobiosis↗
PubMed1978

Pyridine nucleotide interaction with rat liver dihydropteridine reductase.

The interactions of a homogeneous preparation of rat liver dihydropteridine reductase with NADH, NADPH, NAD+, NADP+, and the 1-N6-ethenoadenine derivative of NAD+ have been investigated by fluorescence titration, circular dichroism, equilibrium dialysis, Sephadex G-25 chromatography, and polyacrylamide gel electrophoresis. The procedures indicate that the dimeric enzyme has a definite preference for NADH, but binds only 1 mol of this nucleotide per mol of enzyme. The binary complex of enzyme with NADH is only partially stable to exhaustive dialysis and gel electrophoresis, where it shows greater mobility (0.26) than the free enzyme (0.21); however, the complex can be isolated by Sephadex G-25 chromatography, and characterized with respect to its absorbance spectrum. No ternary complexes are observed when samples of reductase, preincubated with excess NADH, and either the reaction product, 2-amino-4-hydroxy-6,7-dimethyl-5,6,7,8-tetrahydropteridine, or the inhibitor, methotrexate, are subjected to polyacrylamide gel electrophoresis.

Animals↗
PubMed1978

Subunit interactions of Glycera dibranchiata hemoglobin.

The coelomic cells of the polychaete annelid Glycera dibranchiata contain two hemoglobins. The monomer hemoglobin fraction is composed of one major component and two minor components as determined by starch gel electrophoresis and isoelectrofocusing, but is homogeneous as to subunit size as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The polymer hemoglobin fraction has and initial molecular weight of Mn = 125,000 as determined by osmometry, but exhibits an increased state of aggregation upon storage. The quaternary structure of the polymer is constituted of monomeric subunits in a non-covalent state of aggregation as demonstrated by its subunit dissociation inthe presence of propyl urea. The oxygen affinity of the polymer is lower than the monomer but increases with deaggregation. The Bohr effect is present only in the polymer. Cooperativity is also characteristic of the polymer and is pH-dependent. Interestingly, cooperativity increases with intermediate states of polymer deaggregation. By far, the main organic phosphate component of the coelomic red cells is ATP accompanied by small amounts of ADP and GTP. No modulating effect of ATP on the oxygen equilibrium of either polymer or total hemolysate was found.

Animals↗