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Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 487 records · Page 27Linked to original sources
PubMed1975

Functional intermediates in the reaction of membrane-bound cytochrome oxidase with oxygen.

Flash photolysis of the membrane-bound cytochrome oxidase/carbon monoxide compound in the presence of oxygen at low temperatures and in the frozen state leads to the formation of three types of intermediates functional in electron transfer in cytochrome oxidase and reduction of oxygen by cytochrome oxidase. The first category (A) does not involve electron transfer to oxygen between -125 degrees and -105 degrees, and includes oxy compounds which are spectroscopically similar for the completely reduced oxidase (Cu1+alpha3(2+)-O2) or for the ferricyanide-pretreated oxidase (Cu2+alpha3(3+)-O2). Oxygen is readily dissociated from compounds of type A. The second category (B) involves oxidation of the heme and the copper moiety of the reduced oxidase to form a peroxy compound (Cu2+alpha 3(3+)-O2=or Cu2+alpha3(2+)-O2H2) in the temperature range from -105 degrees to -60 degrees. Above -60 degrees, compounds of type B serve as effective electron acceptors from cytochromes a, c, and c1. The third category (C) is formed above -100 degrees from mixed valency states of the oxidase obtained by ferricyanide pretreatment, and may involve higher valency states of the heme iron (Cu2+alpha3(4+)-O2=). These compounds act as electron acceptors for the respiratory chain and as functional intermediates in oxygen reduction. The remarkable features of cytochrome oxidase are its highly dissociable "oxy" compound and its extremely effective electron donor reaction which converts this rapidly to tightly bound reduced oxygen and oxidized oxidase.

Animals↗
PubMed1975

Metabolic responses of the awake cerebral cortex to anoxia hypoxia spreading depression and epileptiform activity.

Using the time sharing fluorometer/reflectometer the measurement of NADH fluorescence as well as the reflected light was obtained from the surface of the awake rat brain cortex. The light was transferred to and from the brain via a flexible light pipe (made of quartz fibers) connected to a cannula implanted permanently above the brain. Exposing the rat to pure nitrogen atmosphere increased the fluorescence (reduction of NADH) by 32.3 +/- 6.1% in comparison to the normoxic fluorescence level. During cortical spreading depression (SD) the NADH fluorescence decreased (oxidation of NADH) by 17.3 +/- 2.8%. Exposing the rat to nitrogen after SD was elicited blocked the oxidation cycle observed during SD. Exposing the awake ras to 10, 7.5 or 5% O2 did not block the response of the brain to spreading depression or to Metrazol applied locally to the cortex. Under hypoxic conditions the brain showed a typical response to SD, namely, an oxidation cycle of NADH except that the duration of the cycle was longer and the decrease in the NADH level was smaller. The EEG activity recovered to normal even under 5%. The same effect of hypoxia was found when Metrazol was applied and epileptic activity was developed.

Animals↗
PubMed1975

Optical and magnetic resonance studies of formate binding to horse liver catalase and sperm whale myoglobin.

The binding of formate ion, a substrate for the peroxidatic reaction of catalase, has been investigated by magnetic resonance techniques. Comparative studies of formate binding to ferric myoglobin have also been performed. The nuclear magnetic relaxation (NMR) rate of formate and water protons is enhanced by the presence of ferric horse liver catalase. The enhancement is not changed significantly by the addition of cyanide, indicating that water and formate are still bound in the presence of cyanide. Formate proton to heme iron distances determined by magnetic resonance techniques indicate that formate does not directly bind to the heme iron of catalase or myoglobin but to the globin, and NMR relaxation occurs as a result of outersphere mechanisms. Evidence that water forms an innersphere complex with the iron atom of the catalase heme is presented. In similar experiments with ferric myoglobin, the addition of cyanide caused a large decrease in the enhancement of the proton relaxation rate of both formate and water, indicating the displacement of water and formate from the heme and the vicinity of the heme, respectively. Broad, high-spin, ferric ion electron paramagnetic resonance absorptions of catalase and myoglobin at room temperature obtained in the presence and absence of formate show that formate does not alter appreciably the heme environment of catalase or myoglobin or the spin state of the heme iron. Studies on the binding of formate to catalase as monitored by changes in the heme absorption spectrum in the visible region show one-to-one stoichiometry with heme concentration. However, the small changes observed in the visible region of the optical spectrum on addition of formate ion are attributed to a secondary effect of formate on the heme environment, rather than direct binding of formate to the heme moiety.

Animals↗
PubMed1975

Isothiocyanates. A new class of uncouplers.

This paper describes the uncoupling effect of three isothiocyanates: p-bromophenylisothiocyanate, 4,4'-diisothiocyanatebiphenyl and beta-naphtylemthylisothiocyanate on the respiration of Ehrlich-Lettré cells and isolated mitochondria. The isothiocyanates are similar to other uncouplers (such as 2,4-dinitrophenol and carbonyl cyanide p-trifluoromethoxyphenylhydrazone) in that they: 1. stimulate respiration of state 4 mitochondria; 2. stimulate mitochondrial ATPase activity; 3. release the inhibition of mitochondrial respiration by oligomycin and 4. inhibit both mitochondrial respiration and mitochondrial ATPase activity at higher molar concentrations. The incoupling activity of these isothiocyanates correlates well with their biological activity. Maximal activation of a latent mitochondrial ATPase activity of rat liver mitochondria in the presence of p-bromophenylisothiocyanate was found at a concentration of 15 muM. The investigated isothiocyanates differ significantly in their solubility in organic solvents and their chemical reactivity. We assume that the greater the partition coefficient in a series of isothiocyanates grouped according to the increasing value of log P (partition coefficient for the system octanol/water, 25 degrees C), the greater will be their uncoupling activity, but only up to a certain degree. Any further increase of log P will be marked by a decrease of this activity.

Adenosine Triphosphatases↗
PubMed1975

The properties of hydrogen peroxide production under hyperoxic and hypoxic conditions of perfused rat liver.

The properties of H2O2 production in the "haemoglobin-free", "non-circulatory" perfused liver of rats were examined. The H2O2 production with 1 mM-lactate and 0.15 mM-pyruvate was 82nmol/min per g of liver or 333nmol/min per 100g body wt. in the liver of fed rats at 30 degrees C. This rate decreased to almost half in the livers of starved and phenobarbital-pretreated rats. When H2O2 production was stimulated by urate infusion, almost all of the H2O2 produced by the uricase reaction was decomposed by the catalase reaction. During the demethylation reaction of aminopyrine, no change in H2O2 production was detected by the present method; thus microsomal H2O2 production observed in isolated subcellular fractions appeared not to contribute significantly to the H2O2 production in the whole organ. Whereas the rate of the glycolate-dependent H2O2 production was halved at an intracellular O2 concentration that caused a 10 percent increase in the reduction state of cytochrome c, the half-maximal rate of H2O2 production with lactate and pyruvate was observed at an O2 concentration that caused a 40 percent increase in the reduction state of cytochrome c in the liver. No further increase in the rates of H2O2 production was obtained by increasing O2 pressure up to 5 times 10(5) Pa. The rate of ethanol oxidation through the catalase "peroxidatic" reaction varied, depending on the substrate availability. The maximal capability of this pathway in ethanol oxidation reached approx. 1.5 mumol/min per g of liver, when a mixture of urate, glycollate and octanoate was infused to enhance H2O2 production.

Aminopyrine↗
PubMed1975

Optical measurement of the catalase-hydrogen peroxide intermediate (Compound I) in the liver of anaesthetized rats and its implication to hydrogen peroxide production in situ.

The spectrophotometric determination of the catalase-H2O2 intermediate (Compound I) was extended to the liver in situ in anaesthetized rats. The rate of H2O2 production was determined for the liver in situ with endogenous substrates, and in the presence of excess of glycollate. Glycollate infusion doubled H2O2 production rate in the liver of air-breathing rats, and caused a fourfold increase when rats breathed O2 at 1 times 10(5) Pa. Hyperbaric O2 up to 6 times 10(5) Pa did not increase H2O2 generation supported by endogenous substrates, nor did it increase H2O2 production above that produced by 1 times 10(5) Pa O2 in glycollate-supplemented rats. The rates of ethanol oxidation via hepatic catalase and via alcohol dehydrogenase in the whole body were separately measured. The contribution of hepatic catalase to ethanol oxidation was found to be approx. 10 percent in endogenous conditions and increased to 30 percent or more of the total ethanol oxidation in rats supplemented with glycolate.

Alcohol Oxidoreductases↗
PubMed1975

Functional intermediates in reaction of cytochrome oxidase with oxygen.

The development of a low temperature kinetic method for the flash photolysis of the compounds of membrane-bound cytochrome a3 with carbon monoxide in the presence of oxygen affords evidence for three categories of functional intermediate compounds of cytochrome a3 and oxygen. The three classes are identified as follows: Compounds of Type A are considered to be "oxy" compounds of the ferrous heme. They have the composition a3-2+. O2. Compounds of Type B are considered to be peroxide compounds (CU-2+A3-3+ O-2= or CU-2+A3-3+ O2H2) or the equivalent heme Fe-Cu peroxide bridge structures. Compounds of Type C are formed from the ferricyanide pretreated oxidase and may involve higher oxidation states of the heme iron such as quadrivalent iron, and peroxide. Kinetic and equilibrium studies show these compounds to be functional in oxygen reduction in the sequence A yields B yield cytochromes a, c, c1, etc.

Animals↗
PubMed1975

12-(9-Anthroyl)stearic acid, a fluorescent probe for the ubiquinone region of the mitochondrial membrane.

1. 12-(9-Anthroyl)stearic acid can be incorporated into mitochondrial membranes. 2. The fluorescence properties of the membrane-bound probe are different from those of the free molecule. 3. The intensity of emission and fluorescence life-time of the probe is enhanced when, in the presence of substrate, the electron-transport chain is reduced. 4. This change in intensity has been demonstrated to be a result of collisional quenching by oxidised ubiquinone in the oxidised membrane but not when the respiratory chain is in the reduced state. 5. In pulsing anaerobic mitochondria with oxygen the rate of the fluorescence change is found to be slower than the rate of ubiquinone oxidation, suggesting that the probe detects a structural transition in the mitochondrial inner membrane. 6. This transition results in a constraint on ubiquinone motion in the reduced system. Model experiments, using lipid dispersions, have been carried out to test some of the interpretations.

Animals↗