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J Barber

Publications and source records attributed to J Barber.

At least 217 records · Page 12Linked to original sources
PubMed1981

Picosecond energy transfer in Porphyridium cruentum and Anacystis nidulans.

Picosecond energy transfer is measured in Anacystis nidulans and Porphyridium cruentum. Fluorescence is sensitized by a 6-ps laser flash, at 530 nm. The time dependence of fluorescence is measured with reference to the laser pulse. Fluorescence is recorded from phycoerythrin (576 nm), R-phycocyanin (640 nm), allophycocyanin (666 nm), Photosystem II chlorophyll (690 nm) and long wave length chlorophyll (715 nm). Energy transfer measurements are made at 37 degrees C, 23 degrees C, and 0 degrees C, and 77 degrees K. It is shown that the rate of energy transfer can be varied with temperature. In both A. nidulans and P. cruentum there is a sequential transfer of excitation energy from phycoerythrin to phycocyanin to allophycocyan to Photosystem II chlorophyll fluorescence. The long wavelength chlorophyll fluorescence at 715 nm, however, does not always follow a sequential transfer of excitation energy. Depending on the temperature, fluorescence at 715 nm can precede fluorescence from phycocyanin.

Cyanobacteria↗
PubMed1981

Relationship between Thylakoid Membrane Fluidity and the Functioning of Pea Chloroplasts : EFFECT OF CHOLESTERYL HEMISUCCINATE.

Cholesteryl hemisuccinate has been incorporated into pea chloroplast thylakoids to investigate the relationship between fluidity and functioning of this membrane system. Levels of sterol which increased the apparent viscosity of the membrane, estimated by fluorescence polarization measurements using the lipophilic probe, 1,6-diphenyl-1,3,5 hexatriene, affected several photosynthetic processes. A decrease in fluidity was accompanied by an inhibition of dark limiting steps associated with electron transfer between photosystems two and one (PSII and PSI) as observed by the oxidation of the primary acceptor of PSII and by electron flow to ferricyanide. Also, treatment with cholesteryl hemisuccinate inhibited the saltinduced rise in chlorophyll fluorescence and changed the ionic conductivity of the membrane as judged by measurements of the decay of the lightinduced proton gradient. The results are discussed in terms of the effect of fluidity changes on the lateral diffusion of plastoquinone and chlorophyll protein complexes in the lipid matrix of the membrane.

Journal Article↗
PubMed1981

Lightweight cassette for mobile-unit radiography.

The authors have developed a cassette system for mobile-unit radiography, using a soft-vinyl cassette in a Lucite housing faced with aluminum. This system performs as well as conventional radiographic cassettes and weighs approximately one-half to one-third as much.

Evaluation Studies as Topic↗
PubMed1981

Grand rounds.

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Aged↗
PubMed1980

Further studies of the relationship between cation-induced chlorophyll fluorescence and thylakoid membrane stacking changes.

Salt-induced changes in thylakoid stacking and chlorophyll fluorescence do not occur with granal membranes obtained by treatment of stacked thylakoids with digitonin. In contrast to normal untreated thylakoids, digitonin prepared granal membranes remain stacked under all ionic conditions and exhibit a constant high level of chlorophyll fluorescence. However, unstacking of these granal membranes is possible if they are pretreated with either acetic anhydride or linolenic acid. Trypsin treatment of the thylakoids inhibits the salt induced chlorophyll fluorescence and stacking changes but stacking of these treated membranes does occur when the pH is lowered, with the optimum being at about pH 4.5. This type of stacking is due to charge neutralization and does not require the presence of the 2000 dalton fragment of the polypeptide associated with the chlorophyll a/chlorophyll b light harvesting complex and known to be lost during treatment with trypsin (Mullet, J.E. and Arntzen, C.J. (1980) Biochim. Biophys. Acta 589, 100-117). Using the method of 9-aminoacridine fluorescence quenching it is argued that the surface charge density, on a chlorophyll basis, of unstacked thylakoid membranes is intermediate between digitonin derived granal and stromal membranes, with granal having the lowest value. The results are discussed in terms of the importance of surface negative charges in controlling salt induced chlorophyll fluorescence and thylakoid stacking changes. In particular, emphasis is placed on a model involving lateral diffusion of different types of chlorophyll protein complex within the thylakoid lipid matrix.

Aminoacridines↗
PubMed1980

The role of membrane surface charge in the control of photosynthetic processes and the involvement of electrostatic screening.

Calculations of changes of the integrated space charge density within the diffuse layer adjacent to a negatively charged membrane surface have been made using analytical expressions derived from the full non-linear Poisson-Boltzmann equation of the Gouy-Chapman theory. This electrostatic screening parameter has been examined for mixed electrolytes of valency type Z1+/Z1- and Z2+/Z1- and concentration ranges were chosen so as to compare with experimental data obtained with thylakoid membranes. The results of the analysis are consistent with previous arguments (Barber, J., Mills, J.D. and Love, A. (1977) FEBS Letts. 74, 174-181) that this screening parameter is involved in the control of salt induced chlorophyll fluorescence and thylakoid stacking changes. Phenomenological equations suggesting the origin of the variations in the integrated space charge density for various salt conditions are presented. Overall the integrated space charge density (sigma chi) is shown to be a more satisfactory measure of both short and long range effects associated with electrostatic screening and double layer repulsion of charged surfaces than the planar space charge density (rho chi).

Chlorophyll↗
PubMed1980

Electrostatic control of chloroplast coupling factor binding to thylakoid membranes as indicated by cation effects of electron transport and reconstitution of photophosphorylation.

1. Increase in electron transport rate and the decay rate of the 518 nm absorption change, induced by EDTA treatment, is prevented by cations. The order of effectiveness is C3+ > C2+ > C+. 2. In this respect methyl viologen is an effective divalent cation in addition to its action as an electron acceptor. 3. Complete cation irreversible EDTA-induced uncoupling occurs in the dark in 2 min. Light greatly stimulates the rate of uncoupling by EDTA. It is concluded that the uncoupling is due to release of coupling factor I from the thylakoid membrane. 4. Binding of purified coupling factor I to coupling factor I-depleted thylakoids can be achieved with any cation. The order of effectiveness is C3+ > C2+ > C+, reconstituted thylakoids are active in photophosphorylation regardless of the cation used for coupling factor I binding. 5. The marked difference in the concentration requirements for cation effects on 9-aminoacridine fluorescence yield and for prevention of uncoupling by EDTA indicate that coupling factor I and its binding site have a lower surface charge density than the net surface charge density of the thylakoid membrane. 6. It is concluded that coupling factor I binding only occurs when negative charges on coupling factor I and its binding site are electrostatically screened by cations. 7. Previously reported examples of uncoupling by low ionic conditions are discussed in relation to the basic concepts of diffuse electrical layer theory.

Cations↗
PubMed1980

Further studies of the thylakoid membrane surface charges by particle electrophoresis.

1. Above pH 4.3 the outer surface of thylakoid membranes isolated from pea chloroplasts is negatively charged but below this value it carries an excess of positive charge. 2. Previously the excess negative charge has been attributed to the carboxyl groups of glutamic and aspartic acid residues (Nakatani, H.Y., Barber, J. and Forrester, J.A. (1978), Biochim. Biophys. Acta 504, 215-225) and in this paper it is argued from experiments involving treatments with 1,2-cyclohexanedione that the positive charges are partly due to the guanidino group of arginine. 3. The electrophoretic mobility of granal (enriched in chlorophyll b and PS II activity) and stromal (enriched in PS I activity) lamellae isolated by the French Press technique were found to be the same. 4. Treatment of the pea thylakoids with trypsin or pronase, sufficient to inhibit the salt induced chlorophyll fluorescence changes, increased their electrophoretic mobility indicating that additional negative charges had been exposed at the surface. 5. Polylysine treatment also inhibited the salt induced chlorophyll fluorescence changes but unlike trypsin and pronase, decreased the net negative charge on the surface. 6. The isoelectric point defined as the pH which gave zero electrophoretic mobility (about 4.3) was independent of the nature of the cations in the suspending medium (monovalent vs. divalent).

Chlorophyll↗
PubMed1980

The relationship between thylakoid stacking and salt induced chlorophyll fluorescence changes.

Salt induced chlorophyll fluorescence increase and thylakoid stacking have been measured under various conditions. 1. Aging of pea chloroplasts led to a loss of salt induced chlorophyll fluorescence increase and thylakoid stacking which is suggested to be due to a decrease in membrane fluidity as measured by 1,6-diphenylhextriene fluorescence polarization. 2. The aging treatment was accompanied by a decreased in surface charge density as indicated by chloroplast electrophoretic mobility measurements. 3. Lowering of the temperature to about 0 degrees C retarded the time courses of salt induced stacking and chlorophyll fluorescence increase. 4. Like aging, addition of linolenic acid led to an inhibition of the salt induced fluorescence and stacking phenomena but in this case there was a concomitant increase in electrophoretic mobility without any detectable change in the polarization of 1,6-diphenylhextriene fluorescence. 5. Maximum stacking occurred in both aged and fresh chloroplasts in a low salt medium at about pH 4.3 and the time course for the pH induced process was rapid and relatively temperature insensitive when compared with salt induced stacking. 6. The chlorophyll a/chlorophyll b ratio was lower for salt induced 'grana' than for pH induced 'grana'. 7. The results are discussed in terms of the hypothesis that changes in the lateral interaction of membrane pigment-protein complexes underlie the salt induced chlorophyll fluorescence increase and thylakoid stacking. It is argued that electrostatic screening by cations leads to the formation of domains of low-charge, fluorescent pigment-protein complexes, seggregated from domains of high-charge, quenching complexes, resulting in a increase in chlorophyll fluorescence yield and stacking at low-charge regions on adjacent membranes. In contrast to this, it is argued that the pH induced stacking occurs because of electrostatic neutralization, a mechanism which would not be expected to induce domain formation and associated chlorophyll fluorescence changes.

Chlorophyll↗
PubMed1980

9-Aminoacridine fluorescence changes as a measure of surface charge density of the thylakoid membrane.

1. When suspended in a low cation-containing medium, chloroplast thylakoid membranes and carboxymethyl-cellulose particles quench the fluorescence from 9-aminoacridine (Searle, G.F.W. and Barber, J. (1978) Biochim. Biophys. Acta 502, 309--320). 2. Relief of this quenching is achieved by adding cations to the suspension medium with the order of effectiveness being C3+ greater than C2+ greater than C+, indicating that the fluorescence acts as an indicator of the surface electrical potential. 3. Using the Gouy-Chapman theory, the differential effect of divalent (methyl viologen) and monovalent (K+) cations has been used to calculate surface charge densities. 4. The calculations indicate that the surface charge density on the thylakoids significantly increases when cations are added to the low cation-containing medium. Under the same conditions the surface charge density of glutaraldehyde-fixed thylakoids and carboxymethyl-cellulose particles remained essentially constant. 5. It is argued that the 9-aminoacridine technique is able to probe localized areas on the membrane surface and that the variability of the surface charge density of untreated thylakoids may be due to redistribution of charges associated with membrane stacking as suggested by Barber and Chow (Barber, J. and Chow, W.S. (1979) FEBS Lett. 105, 5--10).

Aminoacridines↗
PubMed1980

Salt-dependent changes of 9-aminoacridine fluorescence as a measure of charge densities of membrane surfaces.

1. When negatively-charged membranes or particles are added to a solution containing 9-aminoacridine and only low concentrations of salts, fluorescence from the dye molecules is decreased. The quenching mechanism is a result of an increase in concentration of the positively charged dye molecule at the surface (Searle, G.F.W. and Barber, J. (1978) Biochim. Biophys. Acta 502, 309-320). 2. Fluorescence quenching is released on adding salts, the effectiveness being generally dependent on the valency of the action used: C3+ > C2+ > C+, in line with a decrease in the surface potential. 3. The differential effect of cations is analyzed according to the Gouy-Chapman theory to obtain estimates for sigma, the net charge per unit area on a number of different surfaces. 4. It was found that in some cases the estimated value of sigma was not constant for a particular membrane system, but increased with salt concentration. The variation was much diminished, though not eliminated, when more rigid surfaces were examined. 5. An alternative method based on the distribution of a divalent cation (methyl viologen) in the diffuse part of the double layer was also used to estimate the overall charge density. This technique gave values lower than those obtained from 9-aminoacridine fluorescence changes. 6. It is argued that 9-aminoacridine cations distribute near localized, charged areas of surfaces, and that the salt-dependent estimates of sigma partly reflect charge redistribution accompanying changes in electrostatic screening by cations. It appears that 9-aminoacridine is a convenient probe to monitor changes in the heterogeneity of charged membranes.

Aminoacridines↗
PubMed1979

Picosecond time-resolved fluorescence study of chlorophyll organisation and excitation energy distribution in chloroplasts from wild-type barley and a mutant lacking chlorophyll b.

Picosecond time-resolved fluorescence spectroscopy has been used to investigate the fluorescence emission from wild-type barley chloroplasts and from chloroplasts of the barley mutant, chlorina f-2, which lacks the light-harvesting chlorophyll a/b-protein complex. Cation-controlled regulation of the distribution of excitation energy was studied in isolated chloroplasts at the Fo and Fm levels. It was found that: (a) The fluorescence decay curves were distinctly non-exponential, even at low excitation intensities (less than 2 x 10(14) photons . cm(-2). (b) The fluorescence decay curves could, however, be described by a dual exponential decay law. The wild-type barley chloroplasts gave a short-lived fluorescence component of approximately 140 ps and a long-lived component of 600 ps (Fo) or 1300 ps (Fm) in the presence of Mg2+; in comparison, the mutant barley yielded a short-lived fluorescence component of approx. 50 ps and a long-lived component of 194 ps (Fo) and 424 ps (Fm). (c) The absence of the light-harvesting chlorophyll a/b-protein complex in the mutant results in a low fluorescence quantum yield which is unaffected by the cation composition of the medium. (d) The fluorescence yield changes seen in steady-state experiments on closing Photosystem II reaction centres (Fm/Fo) or on the addition of MgCl2 (+Mg2+/-Mg2+) were in overall agreement with those calculated from the time-resolved fluorescence measurements. The results suggest that the short-lived fluorescence component is partly attributable to the chlorophyll a antenna of Photosystem I, and, in part, to those light-harvesting-Photosystem II pigment combinations which are strongly coupled to the Photosystem I antenna chlorophyll. The long-lived fluorescence component can be ascribed to the light-harvesting-Photosystem II pigment combinations not coupled with the antenna of Photosystem I. In the case of the mutant, the two components appear to be the separate emissions from the Photosystem I and Photosystem II antenna chlorophylls.

Chlorophyll↗
PubMed1979

The interaction of an amphipathic fluorescence probe, 2-p-toluidinonaphthalene-6-sulphonate, with isolated chloroplasts.

The amphipathic fluorescence probe, 2-p-toluidinonaphthalene-6-sulphonate has been used to investigate the surface electrical properties of chloroplast thylakoid membranes. The fluorescence yield of 2-p-toluidinonaphthalene-6-sulphonate in aqueous solution increases on addition of hypotonically shocked chloroplast, and the emission maximum shifts towards the blue to 440 nm, although the emission spectrum is somewhat distorted by chloroplast pigment absorption. The intensity of 2-p-toluidinonaphthalene-6-sulphonate fluorescence is further increased on adding salts to the membrane suspension, and changes of greater than 100% are routinely observed. Similar observations have also been made with soya bean phospholipid (azolectin) liposomes. The magnitude of the fluorescence increase is dependent on membrane concentration, being more pronounced at high surface area/suspending volume ratios. The effect of salt addition appears to be that of shielding the fixed negative charges on the membrane surface, thus increasing the fraction of 2-p-toluidinonaphthalene-6-sulphonate molecules at the surface, where the 2-p-toluidinonaphthalene-6-sulphonate has a higher fluorescence yield than in free aqueous solution. This concept is supported by the fact that the effectiveness of salts in increasing 2-p-toluidinonaphthalene-6-sulphonate fluorescence is as predicted by classical electrical double layer theory: governed mainly by the charge carried by the cation with an order of effectiveness C3+ greater than C2+ greater than C+, and not by the chemical nature of the cation or by the nature of its co-ion. It has been argued that the chlorophyll fluorescence yield, controlled by the cation composition of the suspending medium follows the total diffusible positive charge density at the thylakoid membrane surface (Barber, J., Mills, J. and Love, A. (1977) Febs. Lett. 74, 174--181). Although the cation induced 2-p-toluidinonaphthalene-6-sulphonate and chlorophyll fluorescence yield changes show similar characteristics, there are also distinct differences between the two phenomena particularly when cations are added to chloroplasts initially suspended in a virtually cation-free medium. Therefore it is concluded that although both 2-p-toluidinonaphthalene-6-sulphonate and chlorophyll fluorescence yields are governed by the electrical properties of the thylakoid membrane surface, the mechanism controlling their cation sensitivity is not the same.

Cell Membrane↗
PubMed1979

The relationship between the lifetime and yield of the 735 nm fluorescence of chloroplasts at low temperatures.

The lifetime and relative yield of the 735 nm fluorescence of chloroplasts, over a range of low temperatures (-60 to -196 degrees C) where the yield of fluorescence changes markedly, were found to be directly proportional. It is concluded that the species of chlorophyll responsible for the 735 nm fluorescence, C-705, is present over the entire temperature range but is less fluorescent at the higher temperatures because of greater energy transfer to P-700. It is also concluded from attempts to measure the rise-time of the 735 nm fluorescence at -196 degrees C that the rise-time is less than 50 ps.

Chlorophyll↗
PubMed1979

The influence of the thylakoid membrane surface properties on the distribution of ions in chloroplasts.

Thylakoid membranes isolated from peas have been subjected to ionic analyses using the technique of neutron activation. This has allowed the analyses of K+, Na+, Mg2+, Ca2+ and Cl- to be measured simultaneously on the same sample. By varying the ionic composition of the suspending medium it has been shown that these chloroplast membranes have no obvious chemical specificity for the inorganic cations studied and that the major controlling factor is the electrostatic neutralization of the surface negative charges. In agreement with the Gouy-Chapman theory and for the conditions used, divalent cations were preferentially attracted to the membrane surface. This finding, together with the ionic analysis of the unwashed thylakoids and of isolated intact chloroplasts, indicated that the major physiological surface cation is Mg2+ and that K+ is probably the main inorganic cation of the stroma. This conclusion is discussed in terms of counterion movement in response to light induced proton pumping at the thylakoid membrane.

Calcium↗