Search PubMed⌕ Search

Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 379 records · Page 21Linked to original sources
PubMed1982

Optical measurements of oxygen delivery and consumption in gerbil cerebral cortex.

Oxygen metabolism of the cerebral cortex of anesthetized gerbils was monitored by surface fluorescence and reflectance spectrophotometry both in vivo and in specimens freeze-trapped by the surface-freezing technique. Fiber optic light guides were used for optical coupling for determining mitochondrial flavoprotein and pyridine nucleotide fluorescence and for recording dual-wavelength reflectance spectra that indicated the levels of ferrocytochromes aa3 and c + c1 in the cortex and the oxygen saturation of cortical hemoglobin. During anoxic episodes increases in ferrocytochromes aa3 and c + c1 and in reduced pyridine nucleotides and flavoproteins were observed only when the cortical hemoglobin was more than 85% disoxygenated. Indeed the steady-state levels of oxidation-reduction of mitochondrial respiratory-chain components remained constant over a wide range of oxygen delivery, increased reduction being observed only when the fraction of inspired oxygen fell below 6%; these properties of mitochondria in vivo resemble those found in vitro. However, in normoxic animals the absorbance at 605 nm that may arise from ferri- or ferrocytochrome aa3 is larger than would be expected of purified mitochondria and may represent a pool of mitochondria that remains reduced at all levels of tissue oxygenation or a pigment not involved in oxygen metabolism.

Animals↗
PubMed1981

Carbon monoxide- and oxygen-reacting haemoproteins in the mitochondrial fraction from the soil amoeba Acanthamoeba castellanii. Studies at subzero temperatures.

1. Mitochondria-enriched fractions of the soil amoeba Acanthamoeba castellanii contained four haemoproteins that in their reduced forms reacted with CO to give photodissociable CO complexes; these were cytochromes a 3, a 614, b- and c-type cytochromes. 2. Non-photodissociable oxygen-containing compounds were formed at temperatures between -130 and -150 degrees C after photodissociation of CO in the presence of 200 microM-O2, 3. Electron transport, indicated by the oxidation of cytochromes a + a3 and cytochrome c, did not occur until the temperature was raised to -80 degrees C.

Amoeba↗
PubMed1981

Oxygen- or organic hydroperoxide-induced chemiluminescence of brain and liver homogenates.

Oxygenation of anaerobically isolated brain and liver homogenates is associated with chemiluminescence and formation of lipid hydroperoxides, the latter determined by the thiobarbituric acid assay. Light emission and formation of malonaldehyde are 20-fold higher in the brain than in liver; chemiluminescence of both decays when accumulation of malonaldehyde ceases. Exogenous organic peroxides, such as t-butyl hydroperoxide, inhibit the light-emission response to oxygenation by brain homogenate, whereas they enhance that of liver homogenate. t-Butyl hydroperoxide-induced photoemission of liver homogenate shows a polyphasic kinetic pattern that is O2-dependent. The spectral analysis of chemiluminescence arising from brain and liver homogenates on oxygenation shows a spectrum with five emission bands at 420-450, 475-485, 510-540, 560-580 and 625-640 nm. These bands are subjected to intensity changes or shifts of the wavelength whenever t-butyl hydroperoxide is present, either inhibiting or stimulating light emission. The blue-band chemiluminescence, around 435 nm, is possibly due to the weak light emission arising from excited carbonyl compounds [Lloyd (1965) J. Chem. Soc. Faraday Trans. 61, 2182-2193; Vassil'ev (1965) Opt. Spectrosc. (USSR) 18, 131-135], whereas the presence of other bands suggests generation of singlet molecular oxygen either in the process triggered on oxygenation (lipid oxygenation) or after supplementation with organic hydroperoxides. We offer several explanations for the spectral analysis presented here.

Animals↗
PubMed1981

Structural features and the reaction mechanism of cytochrome oxidase: iron and copper X-ray absorption fine structure.

X-ray edge absorption of copper and extended fine structure studies of both copper and iron centers have been made of cytochrome oxidase from beef heart, Paracoccus dentrificans, and HB-8 thermophilic bacteria (1-2.5 mM in heme). The desired redox state (fully oxidized, reduced CO, mixed valence formate and CO) in the x-ray beam was controlled by low temperature (-140 degrees C) and was continuously monitored by simultaneous optical spectroscopy and by electron paramagnetic resonance (EPR) monitoring every 30 min of x-ray exposure. The structure of the active site, a cytochrome a3-copper pair in fully oxidized and in mixed valence formate states where they are spin coupled, contains a sulphur bridge with three ligands 2.60 +/- 0.03 A from Fea3 and 2.18 +/- 0.03 A from Cua3. The distance between Fea3 and Cua3 is 3.75 +/- 0.05 A, making the sulphur bond angle 103 degrees reasonable for sp3 sulphur bonding. The Fea3 first shell has four typical heme nitrogens (2.01 +/- 0.03 A) with a proximal nitrogen at 2.14 +/- 0.03 A. The sixth ligand is the bridging sulphur. The Cua3 first shell is identical to oxidized stellacyanin containing two nitrogens and a bridging sulphur. Upon reduction with CO, the active site is identical to reduced stellacyanin for the Cua3 first shell and contains the sulphur that forms the bridge in fully oxidized and mixed valence formate states. The Fea3 first shell is identical to oxyhemoglobin but has CO instead of O2. The other redox centers, Fea and the other "EPR detectable" Cu are not observed in higher shells of Fea3. Fea has six equidistant nitrogens and Cua has one (or two) nitrogens and three (or two) sulphurs with typical distances; these ligands change only slight on reduction. These structures afford the basis for an oxygen reduction mechanism involving oxy- and peroxy intermediates.

Animals↗
PubMed1981

Mitochondrial regulation of phosphocreatine/inorganic phosphate ratios in exercising human muscle: a gated 31P NMR study.

31P NMR is used to determine the relationship between work output in the exercising human forearm and the steady-state capability of oxidative phosphorylation as measured by the phosphocreatine/inorganic phosphate ratio (PCr/Pi). Exercise intensities (one contraction per 5 sec) permitting comfortable continuation of activity for greater than 1 hr produced PCr/Pi of about 1 for a subject of moderate training. Linear relationships between work rate per unit volume of muscle and the 5-min mean PCr/Pi were found for the subject's left and right arms. The protocol affords sensitive criteria of muscle performance in normal subjects and of biochemical or vascular disease in abnormal subjects. The Pi, PCr, and ATP levels found by 31P NMR represent the initial values in the cycle of contraction and relaxation which permit restitution of resting state 4 prior to the next contraction and the continuation of steady-state work performance.

Arm↗
PubMed1981

Respiratory biogenesis during the cell cycle of aerobically grown Escherichia coli K 12. The accumulation and ligand binding of cytochrome o.

A quantitative assay is described for the measurement of cytochrome o in intact cells of E. coli. The procedure involves flash photolysis of the CO-liganded, reduced enzyme in the absence of O2 at temperatures (approx. -100 degrees C) at which the rate of recombination of CO is immeasurably slow. Other CO-binding pigments known to be present, particularly cytochrome d, are excluded from the photodissociation spectrum under these conditions. Measurement of the content of cytochrome o in bacteria separated into size (and thus age) classes by zonal centrifugation shows that the cytochrome accumulates continuously, probably exponentially, throughout the cell cycle and thus constitutes a constant proportion of cell protein during the cycle. The velocity of recombination of CO with cytochrome o at -65 degrees C is invariant over the cell cycle.

Carbon Monoxide↗
PubMed1981

The light-reversible binding of carbon monoxide to cytochrome a1 in Escherichia coli K12.

Difference spectra at 77 K of intact Escherichia coli K 12 grown under oxygen-limited conditions revealed the presence of cytochrome a1. In the presence of CO, the band of the reduced form, observed in both the alpha and gamma regions of the spectrum, was decreased. Dual-wavelength scanning spectrophotometry at sub-zero temperatures revealed a flash-dissociable CO-binding pigment with a broad band around 595 nm, identified as cytochrome alpha 1. Photolysis in the presence of O2 revealed no such band in difference spectra where the reference spectrum was that of the CO-liganded form, a result consistent with the binding of O2 to cytochrome a1. Repeated cycles of photolysis and recombination of the cytochrome with CO were demonstrated at --46 degrees C. The apparent energy of activation for the reaction with CO was 10.9 kcal mol-1 (45.6 kJ mol-1). The results are discussed in relation to previous assumptions and results regarding ligand binding to cytochrome a1 and the function of this cytochrome in bacterial respiration.

Carbon Monoxide↗
PubMed1981

The reaction of cytochrome o in Escherichia coli K12 with oxygen. Evidence for a spectrally and kinetically distinct cytochrome o in cells from oxygen-limited cultures.

Intact cells harvested from O2-limited batch cultures of Escherichi coli K12 contained high levels of the CO-binding cytochromes d, o and a1. In photodissociation difference spectra (i.e. photolysed minus reduced + CO), a peak at 436 nm and a trough at 415 nm have been assigned to an 0-type cytochrome, and not cytochrome d, by photolysis with white light and an He-Ne laser. The reaction of reduced cytochrome o436 with O2 at sub-zero temperatures involved O2 binding to give intermediate(s) with spectral characteristics similar to those of the reduced oxidase-CO complex. The reaction with O2 at successively higher temperatures (range -98 to -59 degrees C) was accompanied by the formation of a trough (with reference to the CO-liganded state) at 436 nm which eventually shifted to 432 nm, indicative of the oxidized form. The apparent energy of activation at low temperatures was 44.6 kJ mol-1 (10.7 kcal mol-1). There was a linear relationship between the rate of formation of the oxygen compound and the O2 concentration up to about 0.5 mM. The second-order constant for this reaction was 10.9 M-1 s-1 at 100 degrees C, at least 10-fold greater than for the reaction of cytochrome o432 with O2 in cells from vigorously aerated cultures. The reaction of both types of cytochrome o with O2 was not readily reversible in the light or in the dark and was further distinguished from the reaction with CO by the markedly lower velocity of the CO reaction. Comparisons are drawn between the reactions with O2 of cytochrome(s) o in E. coli from O2-sufficient and O2-limited cultures and of mitochondrial cytochrome a3. It is proposed that, like the synthesis of cytochrome d, the formation of cytochrome o436 represents an adaptation of the organism to reduced O2 availability.

Carbon Monoxide↗
PubMed1981

Ultraweak chemiluminescence: a sensitive assay for oxidative radical reactions.

Application of chemiluminescence to the study of lipid peroxidation reactions is based on the occurence of short-lived free radicals and excited states derived from side reactions of the lipid peroxidation process. Thus, the light emission yield is extremely low: 10(-9)-10(15). Chemiluminescence is induced or enhanced by conditions that normally increase lipid peroxidation or that create a peroxidative stress, i.e., toxic effect of hyperbaric oxygen or infusion to the intact organ with organic hydroperoxides. The higher quantum yield of induced-light emission allows a better study of the photoemissive species occurring in the chemiluminescence system; in this regard, spectral analysis is the more accurate method for identifying the chemiluminescence species involved. Since chemiluminescence can monitor continuously the oxidative metabolism of exposed or fiberopatic organs in vivo, it constitutes an adequate tool for the noninvasive study of lipid peroxidation.

Animals↗
PubMed1980

Hydroperoxide-induced chemiluminescence of the perfused lung.

Light-emission of the perfused lung is induced by t-butyl hydroperoxide, giving chemiluminescence yields that oscillate between 800 and 1500 counts/s depending on the site and position of the lung. The response of the perfused lung to infusion with different hydroperoxides gives a pattern similar to that observed with the liver microsomal fraction; ethyl hydroperoxide shows a much higher chemiluminescence yield than the tertiary (t-butyl and cumene)hydroperoxides. Alveolar oedema affected the light-emission of the perfused lung depending on the time at which oedema developed, decreasing light emission on infusion of hydroperoxide in the oedematous lung and increasing it when oedema appeared after the maximal chemiluminescence yield was already achieved. Paraquat, administered in vivo, augmented light-emission by approximately 2-fold. The effect of paraquat was a time-dependent process. Lung chemiluminescence, compared with liver chemiluminescence, needed higher hydroperoxide concentration to induce light-emission.

Animals↗
PubMed1980

Low-temperature spectral and kinetic properties of cytochromes in Escherichia coli K-12 grown at lowered oxygen tension.

Escherichia coli K-12 was grown in batch culture in a medium containing succinate as carbon source, supplemented with casein hydrolysate, and with a rate of oxygen supply that resulted in dissolved O2 tension falling to 10% of saturation in the latter stages of growth. Cytochromes in such cells were qualitatively indistinguishable from those present in cells grown under conditions of vigorous aeration where dissolved O2 tensin remained greater than 80% saturation. Spectra recorded at 77 K and their fourth-order finite difference analyses revealed the absence of cytochrome b-558 and only low concentrations of cytochromes a1 and d(a2). At low temperatures, the reaction of cytochrome o with O2 in intact cells, grown under lowered O2 tension, proceeds through the same stage as observed previously in cells grown with vigorous aeration (Poole, R.K., Waring, A.J. and Chance, B. (1979) Biochem. J. 184, 379-389). However, much higher temperatures are required for comparable progress of the reaction in cells grown at lowered O2 tensions. AT 91 degrees C, the reaction with O2 involves ligand binding to give intermediate(s) with spectral characteristics similar to those of the reduced oxidase-CO complex. Temperatures of approx. -79 degrees C are required for the observation of biphasic kinetics and the attainment of an 'end point' in the reaction, features that are seen at temperatures below -98 degrees C in cells from vigorously-aerated cultures. At -32.5 degrees C, oxidation of cytochrome o is observed. The energy of activation for this reaction at low temperatures is 29.9 kJ x mol-1. Binding with CO, in contrast to binding with O2, is characterized by high photolytic reversibility and appears to be less affected by the degree of aeration of cells during growth.

Cold Temperature↗
PubMed1980

Chemiluminescence of lipid vesicles supplemented with cytochrome c and hydroperoxide.

The increase in light emission of hydroperoxide-supplemented cytochrome c observed on addition of lipid vesicles was related to the degree of unsaturation of the fatty acids of the phospholipids: dipalmitoyl phosphatidylcholine was without effect, whereas dioleoyl phosphatidylcholine and soya-bean phosphatidylcholine enhanced chemiluminescence 2- and 3-fold respectively. Effects on light-emission were similar to those on O2 uptake. The chemiluminescence of the present system was sensitive to cyanide and to the radical trap 2,5-di-t-butylquinol, indicating a catlytic activity of cytochrome c and the presence of free-radical species respectively. Lipid-vesicle enhanced chemiluminescence showed different kinetic behaviours, apparently depending on unsaturation: three phases are described for soya-bean phosphatidylcholine, whereas only one phase was present in mixtures containing dipalmitoyl and dioleoyl phospholipids. Chemiluminescence of lipid vesicles supplemented with cytochrome c and hydroperoxide showed similar kinetic patterns with H2O2 and primary (ethyl) and tertiary (t-butyl and cumene) hydroperoxides. Participation of singlet molecular oxygen, mainly on the phase III of chemiluminescence, is suggested by the increase of light-emission by 1,4-diazabicyclo[2.2.2]-octane as well as by data from spectral analysis.

Cyanides↗