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C E Swenberg

Publications and source records attributed to C E Swenberg.

34 records · Page 2Linked to original sources
PubMed1987

Kinetic flow dichroism study of conformational changes in supercoiled DNA induced by ethidium bromide and noncovalent and covalent binding of benz[a]pyrene diol epoxide.

The dynamic conformational changes due to the noncovalent intercalative binding of ethidium bromide and racemic trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), and the covalent binding of BPDE to supercoiled phi X174 DNA, have been studied by gel electrophoresis and a novel application of a kinetic flow linear dichroism technique. The magnitude of the linear dichroism (delta A) of the DNA oriented in the flow gradient is sensitive to the hydrodynamic shape of the DNA molecule which is affected by the binding of the drug or the carcinogen BPDE. While the linear dichroism of ethidium bromide supercoiled DNA is time independent, the delta A spectra of BPDE-DNA reaction mixtures vary on time scales of minutes, which correspond to the reaction rate constant of BPDE to form 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene hydrolysis products and covalent DNA adducts. The rapid noncovalent intercalation of BPDE causes an initial large increase in delta A (up to 250%, corresponding to the dichroism observed with relaxed circular DNA), followed by a slower decrease in the linear dichroism signal. This decrease in delta A is attributed to the removal of intercalated diol epoxide molecules and the resulting reversible increase in the number of superhelical turns. The kinetic flow dichroism spectra indicate that the noncovalent BPDE-DNA complexes are intercalative in nature, while the covalent adducts are characterized by a very different conformation in which the long axes of the pyrenyl residues are oriented at a large angle with respect to the average orientation of the planes of the DNA bases.(ABSTRACT TRUNCATED AT 250 WORDS)

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1986

Neutron-induced free radicals in oriented DNA.

Samples of oriented DNA containing 30 per cent water were irradiated with neutrons at 77 K. The electron spin resonance (e.s.r.) spectra obtained from these irradiated DNA samples show that the formation of radicals is different when the incident neutrons are parallel or perpendicular to the DNA helix. When the incident neutrons are perpendicular to the DNA helix the e.s.r. spectra of thymine and guanine ionic radicals (T-., G+.) are observed. An additional e.s.r. spectrum corresponding to the hydrogen addition radical on thymine (TH.) is observed when the incident neutrons are parallel to DNA helix. The TH. radical appears to be formed by protonation of T-. .

DNA↗
PubMed1986

In vivo dephosphorylation of WR-2721 monitored by 31P NMR spectroscopy.

The in vivo dephosphorylation of the radioprotective agent S-2-[3-(aminopropylamino)]ethylphosphorothioic acid (WR-2721) in male CD2F1 mice was measured by 31P NMR spectroscopy after i.p. injection. The disappearance of the WR-2721 phosphate NMR signal with time was concurrent with an increase and splitting of the inorganic phosphate NMR signal. The more acidic inorganic phosphate resonance is shown to be attributed to phosphate (inorganic phosphate) in the urine. Using regression first-order kinetic analysis of data, after i.p. injection of 600 mg/kg, the half-life of WR-2721 was determined to be 40.9 +/- 5.9 (S.D.) min (n = 10).

Amifostine↗
PubMed1985

Alteration in calcium-binding activity in synaptosomal membranes from rat brains in association with physical dependence upon ethanol.

The effects of ethanol treatment on calcium-binding activity in synaptosomal membrane fraction from rat brains were studied. The synaptosomal membrane fraction from the hippocampus, the cortex and the cerebellum from control, single dose (6 g/kg), dependent intoxicated (prodromal) and dependent withdrawing (ethanol withdrawal syndrome) rats were used. Two different methods were used for determining the calcium activity in these membrane preparations: the calcium chelator fluorescence probe, chlortetracycline (CTC), was used to measure Ca2+ binding sites in the membranes, and radioactive calcium (45Ca) was used to measure the calcium binding to the synaptosomal membranes. Both methods provided similar conclusions; the calcium activity was higher during the dependent intoxicated phase of the ethanol withdrawal period. The synaptosomal membranes from the hippocampus showed more drastic changes in calcium-binding activity than the cortex and the cerebellum. These results suggest that ethanol dependence is associated with changes in calcium-binding activity in certain areas of the rat brain.

Alcoholism↗
PubMed1985

Increase in phi X174 DNA radiation sensitivity due to electric fields.

The application of an external electric field simultaneously with gamma irradiation to an aqueous suspension of phi X174 DNA (in the RFI form) is shown to increase significantly the number of strand breaks. Tritiated DNA allowed the number of single-strand breaks to be estimated from changes in the scintillation of electrophoretic gel band associated with the fastest mobility moiety. At 400 V (approximately 2400 V cm-1) the corrected increase (corrected for phoresis of DNA on the stainless-steel plates) in the G-value yield is 38%. The increase in damage with field strength appears to follow the increase in reduced dichroism. Dichroism results correspond at 400 V to approximately 10% of the maximum orientation. Our results support the conjecture that this significant increase in DNA-radiation interaction with an electric field is due to field-induced conformation changes in the molecule.

Bacteriophage phi X 174↗
PubMed1979

Quenching of fluorescence by triplet excited states in chloroplasts.

The fluorescence quantum yield in spinach chloroplasts at room temperature has been studied utilizing a 0.5-4.0 mus duration dye laser flash of varying intensities as an excitation source. The yield (phi) and carotenoid triplet concentration were monitored both during and following the laser flash. The triplet concentration was monitored by transient absorption spectoscopy at 515 nm, while the yield phi following the laser was probed with a low intensity xenon flash. The fluorescence is quenched by factors of up to 10-12, depending on the intensity of the flash and the time interval following the onset of the flash. This quenching is attributed to a quencher Q whose concentration is denoted by Q. The relative instantaneous concentration of Q was calculated from phi utilizing the Stern-Volmer equation, and its buildup and decay kinetics were compared to those of carotenoid triplets. At high flash intensities (greater than 10(16) photon . cm-2) the decay kinetics of Q are slower than those of the carotenoid triplets, while at lower flash intensities they are similar. Q is sensitive to oxygen and it is proposed that Q, at the higher intensities, is a trapped chlorophyll triplet. This hypothesis accounts well for the continuing rise of the carotenoid triplet concentration for 1-2 mus after the cessation of the laser pulse by a slow detrapping mechanism, and the subsequent capture of the triplet energy by carotenoid molecules. At the maximum laser intensities, the carotenoid triplet concentration is about one per 100 chlorophyll molecules. The maximum chlorophyll ion concentration generated by the laser pulses was estimated to be below 0.8 ions/100 chlorophyll molecules. None of the observations described here were altered when a picosecond pulse laser train was substituted for the microsecond pulse. A simple kinetic model describing the generation of singlets and triplets (by intersystem crossing), and their subsequent interaction leading to fluorescence quenching, accounts well for the observations. The two coupled differential equations describing the time dependent evolution of singlet and triplet excited states are solved numerically. Using a single-triplet bimolecular rate constant of gammast = 10(-8) cm3 . s-1, the following observations can be accounted for: (1) the rapid initial drop in phi and its subsequent levelling off with increasing time during the laser pulse, (2) the buildup of the triplets during the pulse, and (3) the integrated yield of triplets per pulse as a function of the energy of the flash.

Carotenoids↗
PubMed1979

Analysis of picosecond laser induced fluorescence phenomena in photosynthetic membranes utilizing a master equation approach.

A Pauli master equation is formulated and solved to describe the fluorescence quantum yield, phi, and the fluorescence temporal decay curves. F(t), obtained in picosecond laser excitation experiments of photosynthetic systems. It is assumed that the lowering of phi with increasing pulse intensity is due to bimolecular singlet exciton annihilation processes which compete with the monomolecular exciton decay processes; Poisson statistics are taken into account. Calculated curves of phi as a function of the number of photon hits per domain are compared with experimental data, and it is concluded that these domains contain at least two to four connected photosynthetic units (depending on the temperature), where each photosynthetic unit is assumed to contain approximately 300 pigment molecules. It is shown that under conditions of high excitation intensities, the fluorescence decays approximately according to the (time)1/2 law.

Kinetics↗
PubMed1978

Photovoltages in suspensions of magnetically oriented chloroplasts.

The photovoltage of suspensions of magnetically oriented chloroplasts using polarized light of 680 nm has been measured. The magnitude of the photo e.m.f. depends on the polarization of the light and on its direction of propagation with respect to the oriented thylakoid planes. This photo e.m.f. is qualitatively attributed to the Dember effect which arises when inhomogeneous light absorption gives rise to a gradient of positive and negative charges along x , where x is the direction defined by the propagation vector of the light and which is also the direction joining the two electrodes. The photovoltage obtained with the planes of the oriented thylakoids parallel to x depends on the plane of polarization of the incident light and shows that (1) the magnitude of the photovoltage depends on the absorption coefficient (which itself is polarization dependent) and thus on the magnitude of the charge gradient produced by the inhomogeneously absorbed light, and (2) a charge gradient within the planes of the thylakoids can give rise to the macroscopic photovoltage. While our experimental observations are basically in agreement with those previously reported (Fowler, C.F. and Kok, B.(1974) Biochim. Biophys. Acta 357, 308-318 and Witt, H.T. and Zickler, A. (1973) FEBS Lett. 37, 307-310) for unoriented chloroplasts, their interpretation of the origin of this effect in terms of a transmembrane potential must be modified in view of our results obtained with oriented chloroplasts. The macroscopically observed photovoltage of oriented chloroplasts is due to the creation of charge gradients either parallel or perpendicular to the thylakoid planes by a flash of light, the diffusion of these charges and to differences in the mobilities of the negative and positive charges. This interpretation in terms of the Dember effect is completely consistent with the existence of a transmembrane electric field as proposed by Fowler and Kok, as well as by Witt and Zickler. However, macroscopic measurements of the photovoltage using either oriented or unoriented chloroplast suspensions cannot prove that a transmembrane voltage exists, as previously claimed.

Chloroplasts↗
PubMed1978

A picosecond pulse train study of exciton dynamics in photosynthetic membranes.

The fluorescence decay time of spinach chloroplasts at 77 degrees K was determined at 735 nm (corresponding to the photosystem I emission) using a train of 10-ps laser pulses spaced 10 ns apart. The fluorescence lifetime is constant at congruent to 1.5 ns for up to the fourth pulse, but then decreases with increasing pulse number within the pulse train. This quenching is attributed to triplet excited states, and it is concluded that triplet excitons exhibit a time lag of about 50 ns in diffusing from light harvesting antenna pigments to photosystem I pigments. The diffusion coefficient of triplet excitons is a least 300--400 times slower than the diffusion coefficient of singlet excitons in chloroplast membranes.

Chloroplasts↗
PubMed1975

Temperature and impulse velocity in giant axon of squid Loligo pealei.

Impulse propagation velocity as a function of temperature in the range 5--20degreesC was obtained by external recording from the giant axon of Loligo pealei. The stellar nerve was set into a chamber allowing continuous superfusion, temperature control, and double recording of the impulse. Velocity was calculated from the interval between the spike peaks. The Q10 of velocity was about 1.8. At all temperatures, the velocity increased with time so that only data obtained during the 1st h or 2 could be generally considered to be comparable. Impulse block occurred below --3.4degreesC, in contrast to the giant axon of L. vulgaris, which blocks at about 0degreeC, but at the higher range of temperatures, the velocity in the L. pealei axons was not as well sustained as in those of L. vulgaris. The expected impulse velocity was calculated from Huxley's stability function f(beta) by approximating that function to a fourth-order polynominal and by substituting into it suitable ratios of available Q10 values relating to membrane conductance, ionic current, capacitance, and axoplasmic resistance. The calculation provided an improved fit to published experimental data on L. vulgaris. The difference in slope of the log velocity versus temperature plots, between the presumably warm acclimatized L. vulgaris and the cold-acclimatized L. pealei, was present in both experimental and calculated curves.

Animals↗
PubMedDate not supplied

Dynamics of excitions created by a single picosecond pulse.

A theoretical analysis of bimolecular annihilation in finite domains is presented. A Pauli master equation is formulated for the case of varying incident delta function excitation sources. Expressions for the quantum fluorescence yield and its time dependence are derived. The relationship between the fluorescence yield and the number of hits per domain depends on two parameters: the rate constant of bimolecular exciton annihilation and the dimension of the domain in which this annihilation occurs. Recent experimental results imply that the exciton diffusion constant (D) is large (D approximately to greater than 10(-3) cm2 S-1) and that the photosystem II domains may contain as many as five photosynthetic units. An analysis of the time decay of the fluorescence indicates that, for a few hits per domain, the decay may be considered as exponential but for many hits it becomes non-exponential. Thus the fluorescence decay depends on the intensity of the excitation source and/or on the dimension of the domains. Conditions which change the effective size of the domain may change the shape of the fluorescence decay. Some biological consequences and experimental applications of this theory are presented.

Kinetics↗
PubMedDate not supplied

Unwinding and hydrodynamic flow linear dichroism characteristics of supercoiled DNA covalently modified with two isomeric methylchrysene diol epoxides of different biological activities.

Adducts derived from the covalent binding of two positional monomethyl-substituted isomers of a bay region chrysene diol epoxide to supercoiled pIBI30 DNA (2926 base pairs/genome) were prepared, and their characteristics were investigated by a combination of gel electrophoresis and flow linear dichroism techniques. The 5- and 6-methyl derivatives of trans-1,2-dihydroxy-anti-3,4-epoxy-1,2,3,4-tetrahydrochrysene [(+)-5- and (+)-6-MeCDE, respectively], both with 1R,2S,3S,4R stereochemistry, are characterized by significant differences in their biological activities [Melikian et al. (1988) Cancer Res. 48, 1781-1787]. When covalently bound to plasmid DNA, these two molecules give rise to striking differences in the gel electrophoretic and flow hydrodynamic characteristics of the modified supercoiled DNA. The hydrodynamic flow linear dichroism of linearized DNA molecules (obtained by EcoRI enzyme digestion of covalently closed supercoiled pIBI30 DNA), modified covalently with the highly tumorigenic and mutagenic (+)-5-MeCDE derivative, indicates that flexible joints, bends, or kinks are formed at the site of binding of (+)-5-MeCDE. Slab gel data, as well as ethidium bromide-titration tube agarose gel electrophoresis data, indicate that the formation of (+)-5-MeCDE-DNA lesions causes the removal of superhelical turns with an unwinding angle of 13 +/- 3 degrees per covalently bound polycyclic aromatic residue. In contrast, the biological inactive (+)-6-MeCDE does not significantly alter the characteristics of supercoiled DNA, the unwinding angle is only 2.7 +/- 1 degrees, and the changes in persistence lengths detected by the flow linear dichroism technique are significantly smaller than in the case of (+)-5-MeCDE-DNA adducts.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗