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Biomedical subjects

J Barber

Publications and source records attributed to J Barber.

At least 235 records · Page 13Linked to original sources
PubMed1979

The relationship between nitrous oxide conscious sedation and the hypnotic state.

To evaluate the hypothesis that inhalation of low levels of nitrous oxide-oxygen produces an altered state of consciousness similar to hypnosis, 20 subjects were given three suggestions (analgesia, compulsive behavior, and amnesia) during double-blind administration of either nitrous oxide-oxygen or oxygen. Results suggest that administration of nitrous oxide-oxygen may be of increased clinical usefulness if it is combined with careful use of suggestion.

Anesthesia, Dental↗
PubMed1978

Variable chlorophyll a fluorescence from P-700 enriched photosystem I particles dependent on the redox state of the reaction centre.

1. Photosystem I particles enriched in P-700 prepared by Triton X-100 treatment of chloroplasts show a light-induced increase in fluorescence yield of more than 100% in the presence of dithionite but not in its absence. 2. Steady state light maintains the P-700, of these particles, in the oxidised state when ascorbate is present but in the presence of dithionite only a transient oxidation occurs. 3 EPR data show that, in these particles, the primary electron acceptor (X) is maintained in the reduced state by light at room temperature only when the dithionite is also present. In contrast, the secondary electron acceptors are reduced in the dark by dithionite. 4. Fluorescence emission and excitation spectra and fluorescence lifetime measurements for the constant and variable fluorescence indicate a heterogeneity of the chlorophyll in these particles. 5. It is concluded that the variable fluorescence comes from those chlorophylls which can transfer their energy to the reaction centre and that the states PX and P+X are more effective quenchers of chlorophyll fluorescence than PX-, where P is P-700.

Chlorophyll↗
PubMed1978

Surface charges on chloroplast membranes as studied by particle electrophoresis.

1. Particle microelectrophoresis mobility studies have been conducted with chloroplast thylakoid membranes and with isolated intact chloroplasts. 2. The pH dependence of the electrophoretic mobility indicated that at pH values above 4.3 both membrane systems carry a net negative charge. 3. Chemical treatment of thylakoids has shown that neither the sugar residues of the galactolipids in the membrane nor the basic groups of the membrane proteins having pK values between 6 and 10 are exposed at the surface. 4. However, treatment with 1-ethyl-3(3-dimethylaminopropyl)carbodiimide, together with glycine methyl ester, neutralized the negative charges on the thylakoid membrane surface indicating the involvement of carboxyl groups which, because of their pH sensitivity, are likely to be the carboxyl groups of aspartic and glutamic acid residues. 5. The nature of the protein giving rise to the negative surface charges on the thylakoids is not known but is shown not to involve the coupling factor or the light harvesting chlorophyll a/chlorophyll b pigment . protein complex. 6. No significant effect of light was observed on the electrophoretic mobility of either thylakoids or intact chloroplasts. 7. The striking difference in the ability of divalent and monovalent cations to screen the surface charges was demonstrated and explained in terms of the Gouy-Chapman theory. 8. Calculations of the zeta-potentials for thylakoid membranes gave values for the charge density at the plane of shear to be in the region of one electronic charge per 1500--2000 A2. 9. The significance of the results is discussed in terms of cation distribution in chloroplasts and the effect of cations on photosynthetic phenomena.

Cell Membrane↗
PubMed1978

Induction patterns of delayed luminescence fromisolated chloroplasts. I. Response of delayed luminescence to changes in the prompt fluorescence yield.

1. Using a phosphoroscope, delayed luminescence and prompt chlorophyll fluorescence from isolated chloroplasts have been compared during the induction period. 2. Two distinct decay components of delayed luminescence were measured a "fast" component (from approximately 1 ms to approximately 6 ms) and a "slow" component (at approximately 6 ms). 3. The fast luminescence component often did not correlate with the fluorescence changes while the slow component significantly changed its intensity during the induction period in a manner which could usually be linearly correlated with variable portion of the fluorescence yield change. 4. This correlation was evident after preillumination with far-red light or after allowing a considerable time for dark relaxation. 5. The close relationship between the slow luminescence component and variable fluorescence yield was observed with a large range of light intensities and also in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea which considerably changes the fluorescence induction kinetics. 6. Valinomycin and other antibiotics reduced the amplitude of the 6 ms (slow) luminescence without affecting its relation with the fluorescence induction suggesting possibly that a constant electrical gradient exist in the dark or formed very rapidly in the light, which effects the emission intensity. 7. Changes in salt levels of suspending media equally affected the amplitude of both delayed luminescence and variable fluorescence under conditions when the reduction of Q is maximal and constant. 8. The results are discussed in terms of several models. It is concluded that the model of independent Photosystem II units together with photosynthetic back reaction concept is incompatible with the data. Other alternative models (the "lake" model and photosynthetic back reaction; recombination of charges in the antenna chlorophyll; the "w" hypothesis) were in closer agreement with the results.

Chloroplasts↗
PubMed1978

The involvement of the electrical double layer in the quenching of 9-aminoacridine fluorescence by negatively charged surfaces.

The addition of 9-aminoacridine monohydrochloride to carboxymethyl-cellulose particles or azolectin liposomes suspended in a low cation medium results in a quenching of its fluorescence. This quenching can be released on the addition of cations. The effectiveness of cations is related only to their valency in the series of salts tested, being monovalent less than divalent less than trivalent, and is independent of the associated anions. These results indicate an electrical rather than a chemical effect, and the relative effectiveness of the various cations can be predicted by the application of classical electrical double layer theory. Fluorescence quenching can also be released on protonation of the fixed negatively charged ionisable groups, and the quenching release curve follows the ionisation curve of these groups. We postulate that when 9-aminoacridine molecules are in the electrical diffuse layer adjacent to the charged surface their fluorescence is quenched, probably due to aggregate formation. As cations are added the 9-aminoacridine concentration at the surface falls as it is displaced into the bulk solution, where it shows a high fluorescence yield with a fluorescence lifetime of 16.3 ns. The fluorescence quenching is associated with an absorbance decrease, which is pronounced with carboxymethyl-cellulose particles and can probably be attributed to self-shielding. The negative charges carried by lipoprotein membranes are primarily due to carboxyl and phosphate groups. Therefore these results with carboxymethyl-cellulose (carboxyl) and azolectin (phosphate) support our earlier suggestion that 9-aminoacridine may be used to probe the electrical double layer associated with negatively charged biological membranes.

Acridines↗
PubMed1978

Picosecond time-resolved study of MgCl2-induced chlorophyll fluorescence yield changes from chloroplasts.

The MgCl2-induced chlorophyll fluorescence yield changes in broken chloroplasts, suspended in a cation-free medium, treated with 3,-(3',4'-dichlorophenyl)-1,1-dimethylurea and pre-illuminated, has been investigated on a pico-second time scale. Chloroplasts in the low fluorescing state showed a fluorescence decay law of the form exp --At1/2, where A was found to be 0.052 ps-1/2, and may be attributed to the rate of spillover from Photosystem II to Photosystem I. Addition of 10 mM MgCl2 produced a 50% increase in the steady-state fluorescence quantum yield and caused a marked decrease in the decay rate. The fluorescence deday law was found to be predominantly exponential with a 1/e lifetime of 1.6 ns. These results support the hypothesis that cation-induced changes in the fluorescence yield of chlorophyll are related to the variations in the rate of energy transfer from Photosystem II to Photosystem I, rather than to changes in the partitioning of absorbed quanta between the two systems.

Chlorophyll↗
PubMed1978

Picosecond time-resolved energy transfer in Porphyridium cruentum. Part I. In the intact alga.

The wavelength-resolved fluorescence emission kinetics of the accessory pigments and chlorophyll a in Porphyridium cruentum have been studied by pico-second laser spectroscopy. Direct excitation of the pigment B-phycoerythrin with a 530 nm, 6 ps pulse produced fluorescence emission from all of the pigments as a result of energy transfer between the pigments to the reaction centre of Photosystem II. The emission from B-phycoerythrin at 576 nm follows a nonexponential decay law with a mean fluorescence lifetime of 70 ps, whereas the fluorescence from R-phycocyanin (640 nm), allophycocyanin (660 nm) and chlorophyll a (685 nm) all appeared to follow an exponential decay law with lifetimes of 90 ps, 118 ps and 175 ps respectively. Upon closure of the Photosystem II reaction centres with 3-(3,4-dichlorophenyl)-1,1-dimethylurea and preillumination the chlorophyll a decay became non-exponential, having a long component with an apparent lifetime of 840 ps. The fluorescence from the latter three pigments all showed finite risetimes to the maximum emission intensity of 12 ps for R-phycocyanin, 24 ps for allophycocyanin and 50 ps for chlorophyll a. A kinetic analysis of these results indicates that energy transfer between the pigments is at least 99% efficient and is governed by an exp --At1/2 transfer function. The apparent exponential behaviour of the fluorescence decay functions of the latter three pigments is shown to be a direct result of the energy transfer kinetics, as are the observed risetimes in the fluorescence emissions.

Chlorophyll↗
PubMed1978

Picosecond time-resolved energy transfer in Porphyridium cruentum. Part II. In the isolated light harvesting complex (phycobilisomes).

The transfer of excitation energy between phycobiliproteins in isolated phycobilisomes has been observed on a picosecond time scale. The photon density of the excitation pulse has been carefully varied so as to control the level of exciton interactions induced in the pigment bed. The 530 nm light pulse is absorbed predominantly by B-phycoerythrin, and the fluorescence of this component rises within the pulse duration and shows a mean 1/e decay time of 70 ps. The main emission band, centred at 672 nm, is due to allophycocyanin and is prominent because of the absence of energy transfer to chlorophyll. Energy transfer to this pigment from B-phycoerythrin via R-phycocyanin produces a risetime of 120 ps to the fluorescence maximum. The lifetime of the allophycocyanin fluorescence is found to be about 4 ns using excitation pulses of low photon densities (10(13) photons.cm-2), but decreases to about 2 ns at higher photon densities. The relative quantum yield of the allophycocyanin fluorescence decreases almost 10 fold over the range of laser pulse intensities, 10(13)--10(16) photons-cm-2. Fluorescence quenching by exciton-exciton annihilation is only observed in allophycocyanin and could be a consequence of the long lifetime of the single exciton in this pigment.

Energy Transfer↗
PubMed1978

Dual action of ionophore A23187 on intact chloroplasts.

1. Ionophore A23187 induces uncoupling of potassium ferricyanide-dependent O2 evolution by envelope-free chloroplasts and oxaloacetate-dependent O2 evolution by intact chloroplasts. The half maximal concentration (C1/2) for stimulation of oxygen evolution in both cases is approximately 4 micrometer . 100 microgram chlorophyll . ml-1. 2. Ionophore A23187 also induces inhibition of CO2 and 3-phosphoglycerate-dependent O2 evolution by intact chloroplasts in the presence of 3 mM MgCl2. The half maximal concentrations (C1/2) for inhibition of O2 evolution are 3 micrometer and 5 micrometer respectively . 100 microgram-1 chlorophyll . ml-1. 3. A very high concentration of ionophore A23187 (10 microgram . 20 microgram-1 chlorophyll . ml-1) plus 0.1 mM EDTA lowers the fluorescence yield of intact chloroplasts suspended in a cation-free medium in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicating loss of divalent cation from the diffuse double layers of the thylakoid membranes. 4. These results are discussed in relation to ionophore A23187-induced divalent cation/proton exchange at both the thylakoid and the envelope membranes of intact chloroplasts.

Anti-Bacterial Agents↗
PubMed1978

Fluorescence changes in isolated broken chloroplasts and the involvement of the electrical double layer.

We studied the effects of a variety of cations on chlorophyll fluorescence yield of broken chloroplasts prepared under carefully controlled ionic conditions. In the absence of light-induced electron transport and associated proton pumping, two types of cation-induced chlorophyll fluorescence changes could be distinguished in broken chloroplasts. These are termed "reversible" and "irreversible" fluorescence yield changes. Reversible fluorescence yield changes are characterized by antagonistic effects of monovalent and divalent cations and are prevented by the presence of 5 mM Mg2+ in the suspending media. Reversible-type fluorescence yield changes show little or no dependence on the structure, lipid solubility, or coordination number of the cation, but depend strictly on the net positive charge carried by the ion. It is proposed that these fluorescence changes are brought about through the interaction of monovalent or divalent cations with an electrical double layer at the interface of the outer surface of the thylakoid membrane and the surrounding aqueous solution. The results are interpreted in terms of the Gouy-Chapman theory of the diffuse double layer, indicating that the thylakoid outer surface bears an excess fixed negative charge density of about 2.5 muC/cm2, or approximately 1 negative charge per 640 A2 of membrane surface. Chlorophyll fluorescence quenching in isolated broken chloroplasts suspended in media containing 5 mM MgCl2 is also observed on addition of certain polyvalent cations to the medium. This type of cation-induced fluorescence change appears to be largely irreversible and may occur through specific binding of the cation to the thylakoid as a result of the high electrostatic attraction exerted by the negatively charged membrane surface.

Cations, Divalent↗