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.

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.

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.

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.

Energy transfer and its dependence on membrane properties

With isolated chloroplasts variations in the degree of energy transfer between light-harvesting chlorophyll-protein complexes can be induced by changing the cation content of the suspending medium. The changes can be observed by measuring chlorophyll-fluorescence yields and lifetimes and are probably brought about by conformatial changes in the thylakoid membrane. Detailed studies of the properties of cation-induced changes in chlorophyll fluorescence indicated that the alterations in pigment organization are due to variations in the density of positive charges immediately adjacent to the surface of the thylakoid membrane, being in qualitative agreement with predictions based on the Gouy-Chapman theory of diffuse double layers. Possible mechanisms for the membrane structural changes controlling energy transfer are given.

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.

Psychological, physiological, and pharmacological management of pain

It has been the intent of the authors to impress upon the clinician the multifaceted nature of the human pain experience. We have sought to create an understanding of the emotional nature of pain. The treatment of pain as a pure sensation without directing attention to its behavioral and psychological aspects will generally lead to failure in understanding and ultimately in treating this ubiquitous problem in our profession. The use of drugs alone will have only a minor effect on the treatment of pain. Knowledge of environmental control and an understanding and empathetic approach to the patient in pain or in stress will carry the dentist a long way toward his goal of dental treatment without pain or emotional upset.

Picosecond laser study of fluorescence lifetimes in spinach chloroplast photosytem I and photosystem II preparations

Fractions enriched in either Photosystem I or Photosystem II have been prepared from chloroplasts with digitonin. A more detailed analysis of the decay kinetics of fluorescence excited by a picosecond laser pulse has been possible compared to experiments with unfractionated systems. The Photosystem I fractions show a very short component (less than or equal to 100 ps) at room temperature which is apparently independent of pulse intensity over the range of photon densities used (5 - 10(13)--1 - 10(16) photons cm-2). The Photosystem II fraction has a short initial lifetime at room temperature which is strongly intensity-dependent approaching 500 ps at low photon densities, but decreasing to close to 150 ps at the highest photon densities. All of these room temperature decays appear to be non-exponential, and may possibly be fitted by at t1/2 expression, expected from a random diffusion of excitations via Förster energy transfer. On cooling to 77K, lifetimes of both Photosystem I and Photosytem II increase, the lengthening with Photosystem I being more striking. The Photosystem I decays become intensity dependent like the Photosystem II, and at the lowest photon densities decays which are more nearly exponential within the experimental error give initial lifetimes of about 2 ns. The non-exponential decays seen at high photon densities appear to fit a t1/2 expression.

Hypnosis and suggestion for fitting contact lenses

Language is important in the creation of a painful or non-painful context for fitting contact lenses. This article discusses two types of language use and demonstrates the consequent experience each creates for the patient. The authors also emphasize the importance of acceptance and utilization of responses offered by the patient to further the goals of a comfortable fitting experience. Finally, this article provides an example of a reliable and successful technique for rapidly inducing hypnosis for the purpose of obtaining a comfortable lens fitting.

Release of Particles Containing Metals from Vegetation into the Atmosphere

Studies with radioisotopes indicate that in the laboratory pea plants and pine tree seedlings release zinc and lead into the atmosphere. Field studies carried out on radiolabeled plots vegetated with a variety of grasses and small herbaceous plants also show that these elements are released into the atmosphere. The metals, associated with particles of various sizes, are released from the plant surfaces, and the loss mechanism is influenced by growth conditions, the concentrations of the elements in the leaves, and meteorological factors. For plants whose leaves have about equal concentrations of zinc and lead, the amount of zinc released is usually two orders of magnitude greater than the amount of lead. The significance of the process is discussed in terms of the overall trace metal composition of atmospheric particulates.

Fluorescence lifetimes of Chlorella pyrenoidosa

The flucrescence decay of Chlorella pyrenoidosa has been investigated under a variety of conditions in the picosecond and nanosecond time regions. Most of the fluorescence is accounted for by an expression of the form I(t) = I0exp-(At+Bt1/2) though an additional exponential term is required to include a weak component of lifetime 32 ps observable only at the higher pulse intensities. This interpretation reconciles earlier and apparently conflicting data. The weak 32 ps component may be associated with Photosystem I, although the possibility that it is an artefact of the high intensity pulses used cannot be excluded at present. The main fluorescence, described by the equation above is attributed to the antenna chlorophyll and is of the form which would be expected from a single light harvesting array with trapping at randomly distributed sites.

Cation control of chlorophyll a fluorescence yield in chloroplasts. Location of cation sensitive sites

We have compared the effect of various cations on the fluorescence yield of chloroplasts under several different conditions in vitro. 1. In the absence of a high energy state but in the presence of low (10 mM) concentrations of monovalent cations, divalent metal cations increase steady state chlorophyll a fluorescence yield in a manner which does not involve transport of these cations across the thylakoid membranes. 2. The kinetics of this cation-induced fluorescence rise are relatively slow, and seem to reflect cation binding (or subsequent conformational changes) to sites on the outer surface of the thylakoid membrane. 3. In the absence of monovalent cations, the apparent binding constant for Mg2+ to sites on the outer side of the membrane is low. Addition of low concentrations of monovalent cations (10 mM) competitively inhibits divalent cation binding. 4. Control of fluorescence yield is also exerted by the high energy state, and seems to involve proton/metal cation exchange at sites on the inner side of the thylakoid. 5. When isolated chloroplasts are washed and resuspended in a medium containing no added cations, the initial fluorescence level is high, but is quenched on addition of monovalent cations, sodium EDTA being much more effective than sodium chloride. It is argued that when isolated under these conditions, chloroplasts retain sufficient divalent cations to saturate external negative sites, and that the fluorescence lowering is due to their removal. 6. Some other cations, such as poly(L-lysine), can displace divalent cations from their external sites in an irreversible manner, resulting in a fixed low fluorescence yield.

Enhancement studies on algae and isolated chloroplasts. Part II. Enhancement of oxygen evolution in intact chloroplasts

Intact isolated chloroplasts were shown to exhibit a characteristic three-phase pattern of development of oxygen evolution activity. The first phase, Phase I, appeared to be an equilibration phase in which the isolated chloroplasts adapted to the conditions on the electrode surface. It was characterised by a rapidly increasing rate of oxygen evolution accompanied by decreasing enhancement signals. The second phase, Phase II, was an intermediate phase in which the rate of oxygen evolution was maximal and no enhancement was observed. In the last phase, Phase III, the rate of oxygen fell again, normal enhancement was still missing, but the samples appeared to undergo slow adaptive changes closely related to the State I-State II changes previously reported for whole cell systems. The concentrations of Mg2+ within the chloroplast were shown to play an important role in the control of the development of both the oxygen evolution and enhancement signals. It was shown how these signals could be explained in terms of a model that was consistent with that developed in Part I of this investigation to account for the variability of enhancement of the alga Chlorella pyrenoidosa.

The pharmacokinetics of chlormethiazole following intravenous administration in the aged

Eight healthy aged subjects were administered 1.2 g of chlormethiazole by constant-rate intravenous infusion. The disposition of the drug was found to be multi-exponential in character. Fits of plasma level-time data to two- and three-compartment open models were assessed with the aid of statistical tests. For three of the subjects the experimental data were adequately fitted to a two-compartment pharmakcokinetic model, however a three-compartment model was necessary to fit the data observed for a further four subjects. An anomalous chlormethiazole plasma concentration-time curve was obtained for the remaining subject. The disposition half-life of chlormethiazole was 8.49 +/- 3.28 h and the plasma clearance was 16.14 +/- 5.00 ml/min/kg. These values were significantly different to those reported earlier for young adult subjects and the clinical implications have been discussed. The blood/plasma concentration ratio of chlormethiazole was found to be approximately one with some evidence for concentration dependence.

Availability of monovalent and divalent cations within intact chloroplasts for the action of ionophores nigericin and A23187

1. A23187 will uncouple electron transport by broken chloroplasts in a divalent cation dependent manner provided that they have been treated with a low concentration of EDTA. 2. A23187 stimulates oxaloacetate-dependent oxygen evolution and inhibits phosphoglycerate reduction by intact chloroplasts isolated in a cation-free medium whereas the full effect of nigericin was dependent on the presence of external K+. 3. Uncoupling of oxaloacetate reduction by A23187 in intact chloroplasts is inhibited by EDTA and this effect is overcome by excess Mg2+. 4. The results suggest that divalent and not monovalent cations are available for collapsing the light-induced H+ gradient within the intact organelle.

Chronic leg ulceration in a patient with leprosy

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Chloride transport in Anacystis nidulans

Anacystis nidulans will take up and accumulate chloride ions. When the external concentration was 0.2 mM Cl(-) the level in the cells was 2.8 mM Cl(-) and under these conditions the flux across the cell surface was in the region of 10(-13)equiv Cl(-)·sec(-1)·cm(-2). It is suggested that this Cl(-) influx is active and operates against an electrochemical potential gradient estimated to be 117 mV or 2.68 kcal/mole. The uptake of (36)Cl was inhibited by low temperatures and there was a net loss of Cl(-) from the cells with the level decreasing towards the equilibrium value as estimated from K(+) distribution. Although the active influx of Cl(-) was often stimulated by light this was not always the case. Dark storage treatment and regulation of the chlorophyll a/phycocyanin ratios as well as total pigment content of the cells did not clarify the conditions which brought about light stimulation. Moreover, the metabolic inhibitors CCCP and CMU and also the use of anaerobic conditions did not clearly indicate the relationship between the influx mechanism and light-dark metabolism and no firm conclusions could be made about the nature of the energy source. The variation in the degree of light stimulation probably reflects the fact that in this procaryotic organism the photosynthetic and respiratory units are located on the same membrane systems and are in very close proximity to the probable site of the Cl(-) pump, the plasmalemma.

The Relation between Photophosphorylation and Delayed Light Emission in Chloroplasts

One millisecond delayed light emission has been studied in isolated coupled lettuce (Lactuca sativa var. romaine) chloroplasts. Delayed light emission was increased upon addition of ferricyanide or 2,3,5,6-tetramethyl-p-phenylene diamine. In the presence of ferricyanide, the magnitude of the signal was increased by the addition of ADP (in the absence of orthophosphate), ATP, DI0-9, or phlorizin. The signal was also increased by the addition of NaCl and by the addition of NH(4)Cl in the presence of a high NaCl concentration. The signal of delayed light emission was decreased by the addition of gramicidin, valinomycin, and by the addition of NH(4)Cl in the presence of a low NaCl concentration.Phosphorylation, whether started by addition of ADP or by addition of glucose plus hexokinase plus ATP, caused a significant decrease in delayed light emission. It was concluded that the magnitude of delayed light emission reflects the size of the proton motive force across the thylakoid membrane. Calibration of delayed light emission by creating KCl gradients indicated that the value for the electrochemical potential gradient for H(+) in the presence of ferricyanide was at least 155 millivolts decreasing to 134 millivolts after the onset of phosphorylation.

Cation regulation in Anacystis nidulans

Anacystis nidulans accumulates K(+) in preference to Na(+). The majority of the internal K(+) exchanges with (42)K by a first order process at rates of about 1.3 pequiv·cm(-2)·sec(-1) in the light and 0.26 pequiv·cm(-2)·sec(-1) in the dark. Although the K(+)/K(+) exchange was stimulated by light and inhibited by 10(-4) M CCCP and 10(-5) M DCMU there are several indications that this cation is passively distributed in Anacystis. Inhibition of the exchange by CCCP and DCMU occurred at concentrations greater than those required to inhibit photosynthesis and the K(+) fluxes were stimulated by low temperatures. Moreover, although valinomycin stimulated the exchange this compound did not induce a net K(+) leak. Assuming K(+) is passively distributed and in free solution within the cytoplasm, as indicated by osmotic studies, would imply that there is an active Na(+) extrusion pump operating in this organism. As yet there are no firm conclusions about the nature of the energy source for this efflux pump.

Sodium transport in Na(+)-rich Chlorella cells

The rate of Na(+)/Na(+) exchange as measured with (24)Na(+) in Na(+)-rich cells of Chlorella pyrenoidosa is governed by a single rate constant and saturates with increasing external Na(+) concentration. The K mvalue for this process is 0.8 mM Na(+) and the maximum rate of exchange in illuminated cells is about 5 pmoles cm(-2) sec(-1). These values contrast with a K mof 0.18 mM K(+) and maximum rate of about 17 pmoles K(+)·cm(-2)·sec(-1) for net K(+) influx. Although the Na(+)/Na(+) exchange was only slightly sensitive to light it was inhibited by the uncouplers CCCP and DNP and by the energy transfer inhibitor DCCD. This inhibition of the rate of Na(+)/Na(+) exchange was not accompanied by a loss of internal Na(+). Both the effect of external K(+) on (24)Na(+) influx into Na(+)-rich cells and the inhibition of net K(+) uptake by the presence of external Na(+) indicates that Na(+)/Na(+) and K(+)/Na(+) exchanges share the same carrier and that the external site of this carrier has a three to four times higher affinity for K(+) over Na(+).

Uptake of mercury by Chlorella and its effect on potassium regulation

Addition of mercuric chloride at concentrations which resulted in an overall binding level of about 8 mmoles Hg/l packed cells and above caused a breakdown in the permeability of the cell membrane as indicated by a net efflux of internal K(+). Below this level in region of 2 mmoles Hg/l packed cells the rate of K(+) transfer across the cell surface was stimulated without affecting the internal K(+) level. Maintainence of the stimulation was dependent both on time and dose. Enhancement of the rate of K(+) turnover was associated with a fast component of the inorganic mercury uptake which could be removed by washing with cysteine. The mercury stimulated K(+)/K(+) exchange was inhibited by low temperature, by the uncoupler CCCP and the energy transfer inhibitor DCCD. Overall binding concentrations of inorganic mercury below 0.5 mmoles/l packed cells had no effect on the K(+) transport system. In contrast to mercuric chloride, methyl mercuric chloride over similar concentration ranges did not seem to induce a breakdown in the permeability barrier or directly interact with the K(+)/K(+) exchange but more likely influenced the latter by inhibiting intracellular processes.