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PubMed1979

Oxidation of horseradish peroxidase compound II to compound I.

In the reaction between equimolar amounts of horseradish peroxidase and chlorite, the native enzyme is oxidized directly to Compound II (Hewson, W.D., and Hager, L.P. (1979) J. Biol. Chem. 254, 3175-3181). At acidic pH but not at alkaline values, this initial reaction is followed by oxidation of Compound II to Compound I. The highly pH-dependent chemistry of Compound II can be readily demonstrated by the reduction of Compound I, with ferrocyanide at acidic, neutral, and alkaline pH values. Titration at low pH yields very little Compound II, whereas at high pH, the yield is quantitative. Similarly, the reaction of horseradish peroxidase and chlorite at low pH yields Compound I while only Compound II is formed at high pH. At intermediate pH values both the ferrocyanide reduction and the chlorite reaction produce intermediate yields of Compound II. This behavior is explained in terms of acidic and basic forms of Compound II. The acidic form is reactive and unstable relative to the basic form. Compound II can be readily oxidized to Compound I by either chloride or chlorine dioxide in acidic solution. The oxidation does not occur in alkaline solution, nor will hydrogen peroxide cause the oxidation of Compound II, even at low pH.

Ferrocyanides↗
PubMedDate not supplied

[NADPH-dependent oxidation in endoplasmic reticulum of rat liver after valexon administration].

Changes of different type are detected in components of NADPH-dependent oxidation. The changes begin in different periods (1, 5, 15 days) after administration of valexon to the animals. In the first day the hydroxylase activity is inhibited against a background of the uridine diphosphate glucuronyl transferase activity increase and intensification of ascorbic acid excretion with urine. Five days after the uridine diphosphate glucuronyl transferase activity becomes normal, the ascorbic acid excretion remains intensified and the demethylase and hydroxylase activities increase. Fifteen days later the hydroxylase activity becomes normal, but the demthylase activity and intensity of ascorbic acid excretion are still increased.

Aminopyrine N-Demethylase↗
PubMed1976

Hydrogen exchange at the amide group of reduced pyridine nucleotides and the inhibition of that reaction by dehydrogenases.

Stopped flow ultraviolet spectroscopy has been used to measure the rate of hydrogen exchange with solvent at the amide group of reduced nicotinamide nucleotide coenzymes. Several mechanisms for the exchange reaction are considered in the light of the kinetic data. Complex formation between the coenzyme and any of four dehydrogenases markedly slows the rate of hydrogen exchange. Hydrogen bond formation and/or hydrophobic interactions within these complexes are thought to be the reasons for the decreased rate of exchange.

Alcohol Oxidoreductases↗
PubMed1978

[Metabolic effects of barbiturates on the anoxic brain:free radical trapping].

Different mechanisms have been proposed to explain the protector effect of barbiturates in cerebral ischemia. Among these is the particularly attractive hypothesis that the protection is obtained by an inhibition of the oxydo-reduction process in the respiratory chain in the mitochondria upstream of the Q coenzyme. Keeping this enzyme in the quinone state prevents the formation of the three radical at the level of lipoid complexes of the cellular and sub-cellular membranes, thus assuring the upkeep of the integrity of these structures. The absence of the free radicals equally protects the morphology of the endothelium, in limiting the aggregation of platelets in the arterial vessel lumens. The existence of the three radicals in the organism and their noxious effects are well established, however, that the protection brought about by the barbiturates be the results of free radical trapping remains still an hypothesis.

Barbiturates↗
PubMed1979

[Cytochrome P-450 catalyzed oxidation of 1-piperidinoanthraquinone].

Oxidation of 1-piperidinoantraquinone (1-PA) in microsomal fractions of rat liver was studied. The only product of complete oxidation of 1-PA--(N-antraquinone-1)-delta-aminovaleric acid-was identified using paper and thin-layer chromatography. The participation of cytochrome P-450 in oxidation of 1-PA was demonstrated by sharp inhibition, involving blowing of the microsomes with CO and treatment with sodium deoxycholate. Studies of differential spectra of cytochrome P-450 in the presence of 1-PA are indicative of the first type of binding between 1-PA and cytochrome P-450. The binding constants (Ks) and the kinetic parameters (Km and V) for the above substrate in control microsomes and in those induced by phenobarbital and 3-methyl cholanthrene were determined. The results obtained suggest that cytochrome P-450 is involved in oxidation of a number of heterocyclic compounds resulting in the opening of the ring.

Animals↗
PubMed1979

[Effect of intersubunit interaction in horse liver alcohol dehydrogenase on the kinetics of ethanol oxidation].

The kinetics of enzymatic oxidation of ethanol in the presence of alcohol dehydrogenase within a wide range of ethanol and NAD concentrations (pH 6.0--11.5) were studied. It was shown that high concentrations of ethanol (greater than 0.7--5 mM, depending on pH) and NAD (greater than 0.4--0.8 mM) activate alcohol dehydrogenase from horse liver within the pH range of 6.0--7.9. A mechanism of activation based on negative cooperativity of ADH subunits for binding of ethanol and NAD was proposed. The catalytic and Michaelis constants for alcohol dehydrogenase were calculated from ethanol and NAD at all pH values studied. The changes resulting from the subunit cooperativity were revealed. The nature of ionogenic groups of alcohol dehydrogenase, which affect the formation of complexes between the enzyme and NAD and ethanol, and the rate constants for catalytic oxidation of ethanol was assumed. The biological significance of the enzyme capacity for activation by high concentrations of ethanol within the physiological range of pH in the blood under excessive use of alcohol is discussed.

Alcohol Oxidoreductases↗
PubMed1979

The effects of X-irradiation on lens reducing systems.

Studies have been made of the effects of X-ray on various lens reducing systems, including the levels of NADPH and glutathione (GSH), the activity of the hexose monophosphate shunt (HMS) and of certain enzymes, including GSH reductase, GSH peroxidase, and glucose-6-phosphate dehydrogenase (G-6-PG). It was found that during several weeks following X-irradiation but prior to cataract formation, there was very little change in the number of reduced -SH groups per unit weight of lens protein but that, with the appearance of cataract, there was a sudden loss of protein -SH groups. In contrast, the concentration of GSH in the X-rayed lens decreased throughout the experimental period. Similarly, the concentration of NADPH in the X-rayed lens was found to decrease significantly relative to controls 1 week prior to cataract formation, and the ratio of NADPH to NADP+ in the lens shifted at this time period from a value greater than 1.0 in the control lens to less than 1.0 in the X-rayed lens. A corresponding decrease occurred in the activity of the HMS in X-rayed lenses as measured by culture in the presence of 1-14C-labeled glucose, G-6-PD was partially inactivated in the X-rayed lens. Of the eight enzymes studied, G-6-PD appeared to be the most sensitive to X-irradiation. The data indicate that X-irradiation results in a steady decrease in the effectiveness of lens reducing systems and that when these systems reach a critically low point, sudden oxidation of protein -SH groups and formation of high-molecular-weight protein aggregates may be initiated.

Animals↗
PubMed1979

Dihydrofolate reductase from Lactobacillus casei. Stereochemistry of NADPH binding.

The NADPH molecule binds to dihydrofolate reductase in an extended conformation. Several of the individual dihedral angles, especially in the adenine mononucleotide portion of the coenzyme, differ from their minimum energy conformations. The ribose phosphate portions of the coenzyme are involved in numerous specific hydrogen-bonded and charge-charge interactions. The adenine ring resides in an apparently nonspecific hydrophobic cleft and the nicotinamide ring is bound within an intricately constructed cavity, one wall of which includes the pyrazine ring of bound methotrexate. Two rather extended loops (residues 10 to 24 and 117 to 135) connecting beta A to alpha B and beta F to beta G, respectively, move 2 to 3 A when NADPH binds to dihydrofolate reductase. No overall structural homology is evident between the dinucleotide binding domains of dihydrofolate reductase on the one hand and the four NAD+-dependent dehydrogenases of known structure on the other. However, binding does occur in both cases at the carboxyl edge of a region of parallel beta sheet flanked by a pair of alpha helices.

Binding Sites↗
PubMed1979

Effect of clofibrate treatment on acylcarnitine oxidation in isolated rat liver mitochondria.

The oxidation of palmitoyl- and octanoylcarnitine in liver mitochondria from normal and clofibrate-treated male rats was studied by measuring the ADP-stimulated oxygen consumption and acetyl group production (the sum of formed ketone bodies, acetylcarnitine and citrate). In the absence of malate the treatment approximately doubled the rate of acylcarnitine oxidation. In normal mitochondria the acetyl groups consisted almost totally of ketone bodies. The clofibrate-induced increase in acetyl group production was attributable to enhanced rates of ketone body and acetylcarnitine formation. The observed increase in acylcarnitine oxidation was associated with an elevated beta-hydroxybutyrate: acetoacetate ratio, reflecting an increased mitochondrial NADH:NAD+ ratio. In normal mitochondria the addition of malate in the presence of fluorocitrate doubled the rate of beta oxidation by forming citrate. The beta oxidation in mitochondria from clofibrate-treated rats was virtually unresponsive to added malate. The clofibrate-induced increase in ketogenesis was confirmed in disintegrated mitochondria. The treatment approximately doubled the rate of ketone body production from acetyl-CoA in disrupted organelles. The enhanced capacity of ketogenesis was accompanied by increased activity of the specific acetoacetyl-CoA thiolase (EC 2.3.1.8), which is the first step enzyme of the pathway. Clofibrate administration also increased the activities of general oxoacyl-CoA thiolase (EC 2.3.1.16), palmitoyl-CoA dehydrogenase (EC 1.3.99.3), and butyryl-CoA dehydrogenase (EC 1.3.99.2), which all take part in the beta oxidation of fatty acids.

Acetoacetates↗
PubMedDate not supplied

[Mathematical model of Thiobacillus ferrooxidans growth on a medium with ferrous iron].

A mathematical model is proposed for the growth of Thiobacillus ferrooxidans in the process of Fe2+ oxidation depending on the active acidity and temperature of the medium. The model was used to establish the correlation between the action of temperature and pH of the medium on the bacterial growth and oxidation of Fe2+. The range of pH values which had no effect on the bacterium is broader at 28 degrees C (from 2.5 to 2.8) than at 12 degrees C (from 2.3 to 2.4). Apparently, the growth of the bacterium and the enzymatic processes of Fe2+ oxidation are more susceptible to changes in the pH than in temperature, at least when it is lowered to 12 degrees C.

Culture Media↗
PubMed1978

Oxidation of hypotaurine to taurine by ultraviolet irradiation.

Oxidation of hypotaurine to taurine is known to occur in vivo. Search for an enzyme performing that oxidation has been unsuccessful. However, fast and quantitative oxidation of hypotaurine (and other sulfinates) by ultraviolet irradiation has now been observed. The reaction is first order and pH-dependent, and its rate depends strongly on the kind of sulfinate irradiated. Only the corresponding sulfonate is recovered as the product under the relatively mild conditions used. Catalase or superoxide dismutase does not affect the oxidation, which is oxygen-dependent. A simple reaction scheme is proposed to account for the findings.

Cysteine↗
PubMedDate not supplied

[Induction of ion transport coupled to oxidative reactions in the membranes of mitochondria and liposomes].

The mechanism of induction of potassium permeability for mitochondrial membranes under special conditions was under study. Conditions were such as: 1--incubation of mitochondria in medium with low meaning of pH (6,0--6,5), 2--incubation in preseace of electrophylic agent--p-(N,N-di-2-chloroethyl) aminophenylacetic acid, which is hydrolized to HCl and 3-lipidsoluble acid, 2,4-dinitrophenol. It is shown that the named mechanism in any case requires the oxidation of lipids of mitochondrial membranes.

Anaerobiosis↗