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J J Brand

Publications and source records attributed to J J Brand.

At least 19 recordsLinked to original sources
PubMed2001

Algae permeability to Me(2)SO from -3 to 23 degrees C.

Biphasic transport of water and dimethyl sulfoxide (Me(2)SO), a common cryoprotective agent (CPA), in algal cells was induced and measured on a cryoperfusion stage. A two-step experimental protocol provided data for the volumetric response of Chlorococcum (C.) texanum to impermeable and permeable solutes. First, the cells were exposed to a 500-mOsm sucrose solution, causing immediate shrinkage of the cell to a minimum equilibrium volume. Then an isoosmotic 200-mOsm/300-mOsm CPA/sucrose solution was introduced to the cells, resulting in increased cell volume to a new equilibrium state. Experiments were conducted at temperatures between -3 and 23 degrees C. Cell volumes were measured off-line by computer analysis of video images. A network thermodynamic model was fit to the transient volume data to determine permeabilities of C. texanum to water and Me(2)SO over the full temperature range, and results were calculated with two numeric methods. Biphasic transport was found to be slower at colder temperatures, with water entering the cell faster than Me(2)SO. Experimental results were also compared with data from similar experiments using methanol (MeOH) as the CPA. MeOH influx was calculated to be a magnitude larger than that of water. Additionally, MeOH permeability was at least three orders of magnitude greater than Me(2)SO permeability, and the difference in these solute permeabilities increased as temperature decreased.

Biological Transport, Active↗
PubMed1998

Measurement of cell volume loss in the liquid region preceding an advancing phase change interface.

It is well understood that the solidification of a solution results in a redistribution of solute in the liquid zone. For the freezing of suspensions of cells it is anticipated that accumulation of solute in the region leading a growing ice phase will cause an osmotic response in cells before the ice phase reaches the cells. To measure this phenomenon in a specific algal species, the volume changes in Chlorococcum texanum during freezing were studied using directional solidification cryomicroscopy. The relative cell volume was tracked continuously as a function of temperature and position as cells encountered the moving phase front. The loss of cell volume was measured in the liquid region containing concentrated solute ahead of the growing solid phase.

Cell Size↗
PubMed1989

A Mössbauer analysis of the low-potential iron-sulfur center in photosystem I: spectroscopic evidence that FX is a [4Fe-4S] cluster.

We report the results of a Mössbauer study of the low-potential iron-sulfur cluster FX in the Photosystem I core protein of Synechococcus 6301. The Mössbauer spectrum of FX in the oxidized state shows an isomer shift of 0.42 mm/s, which is in good agreement with the 0.43 mm/s isomer shift found in [4Fe-4S] proteins but not with the isomer shift of 0.26 mm/s found in [2Fe-2S] proteins. In the reduced state the spectrum is asymmetrically broadened at 80 K, indicating the presence of two very closely spaced doublets with an average isomer shift of 0.55 mm/s, which is also in agreement with [4Fe-4S] proteins. At 4.2 K, the spectrum exhibits broadening and magnetic splitting similar to what is observed for [4Fe-4S] proteins and quite unlike [2Fe-2S] proteins. Given the assumption that the iron atoms of FX are tetrahedrally coordinated with sulfur ligands, the data strongly support the assignment of FX as a [4Fe-4S] cluster.

Chlorophyll↗
PubMed1989

Sequential Events in the Photoinhibition of Synechocystis under Sodium Stress.

Synechocystis (PCC 6714) is photoinhibited at low photon flux density when illuminated in medium devoid of Na(+). Photosynthetic activity and variable fluorescence yield were measured in intact cells during the course of inhibition and during recovery from inhibition in order to characterize sequential inhibitory events. Photosystem II antenna chlorophyll becomes functionally disconnected from the reaction center in the first stage of inhibition, although energy is still transferred from phycobilin pigments to the reaction center. This occurs simultaneously with, or subsequent to, the previously observed (J Zhao, JJ Brand [1988] Arch Biochem Biophys 264: 657-664) inactivation of O(2)-evolution units in Na(+)-stressed cells. Addition of Na(+) to the culture medium rapidly restores the O(2)-evolving system, but reassociation of photosystem II antenna chlorophyll is much slower and requires new protein synthesis. A site nearer to the reaction center of photosystem II becomes inactivated in a secondary inhibitory event. Recovery from secondary inhibition occurs slowly and requires protein synthesis. Cells recovering from secondary inhibition produce active photosystem II units with a fully functional complement of antenna chlorophyll. Synechocystis is photoinhibited in complete (Na(+)-containing) medium when illuminated at high photon flux density. These photoinhibited cells exhibit the same recovery behavior as cells at the second stage of inhibition in Na(+)-deficient medium.

Journal Article↗
PubMed1988

Sequential effects of sodium depletion on photosystem II in Synechocystis.

Incubation of Synechocystis PCC 6714 in liquid medium devoid of Na+ results in a light-dependent loss in photosynthetic O2 evolving capacity within 1 h. Photosynthetic activity is fully restored and normal growth resumes after Na+ is supplied to culture medium of depleted cells. If external Na+ is provided as soon as inhibition becomes complete, normal photosynthesis is restored within 3 min. However, if cells are further illuminated for several h under Na+ stress, then full recovery takes much longer, and requires new protein synthesis. Electron transport assays using isolated membranes demonstrate that the immediate inhibition resulting from Na+ depletion involves the O2 evolving site, while the secondary effect requiring new protein synthesis occurs near the reaction center of Photosystem II. Experiments conducted at different pH values and in the absence of inorganic carbon demonstrate that within the short time duration of these experiments Na+ does not inhibit photosynthesis by restricting bicarbonate movement into the cells. These experiments extend previous results with other cyanobacteria which demonstrated that Ca2+ and Na+ stress cause reversible damage at a site near the reaction center of Photosystem II. The damage can be characterized as a primary ion effect at the oxygen evolving site and a secondary photoinhibition near the reaction center of Photosystem II.

Bicarbonates↗
PubMed1985

Anacystis nidulans Demonstrates a Photosystem II Cation Requirement Satisfied Only by Ca or Na.

Anacystis nidulans exhibits a total loss of photosystem II (PSII) activity upon incubation in a nutrient medium deficient in Ca(2+) and Na(+) and containing a divalent cation chelator. This loss of activity is light-dependent, which corresponds to an energy requirement. Likewise, Ca(2+) efflux takes place only in cells incubated in light. The loss of PSII activity is reversible by addition of submillimolar amounts of either Ca(2+) or Na(+) to the external medium but not by the addition of any other cation. Restoration of lost PSII activity also requires light. Light saturation curves for partially depleted cells demonstrate both lower maximum O(2) evolution rates and decreased relative quantum yields when compared to control cells. Partial electron transport reactions isolate the site of the Ca(2+)/Na(+) effect to the reaction center itself or immediately on its oxidizing side and exclude the water-splitting complex. O(2) flash yields decline during cation depletion, indicating a decrease in the number of functional PSII reaction centers, but the maximum turnover rate for still functional reaction centers does not decline. Thus, PSII of A. nidulans exhibits an all-or-none cation requirement, satisfied only by Ca(2+) or Na(+).

Journal Article↗
PubMed1984

Evidence for direct roles of calcium in photosynthesis.

Calcium may function directly in several aspects of photosynthesis. It appears to modulate activity of the phosphatase enzymes in the carbon reduction cycle and also to regulate chloroplast NAD+ kinase activity through a calmodulin-like protein. Some evidence supports a calcium function in the water-splitting complex, and other evidence indicates a reaction center function in photosystem II. Calcium in reaction center II may be tightly bound in chloroplasts and weakly bound in blue-green algal thylakoids. Free calcium concentration in stroma is probably less than 10(-6) M, although the absolute concentration is not yet known. Intrathylakoid calcium content is likely very high. Stromal calcium may regulate several enzyme activities, while intrathylakoid calcium may promote photosystem II constitutively. Results to date demonstrate the need for more attention to cation composition in studies of both light and dark reactions of photosynthesis, and the need to identify free calcium levels in chloroplasts.

Calcium↗
PubMed1980

Role of divalent cations and ascorbate in photochemical activitis of Anacystis membranes.

Photosynthetic membrane fragments were prepared from Anacystic nidulans by French pressure cell disruption. Ascorbate was required to stabilize photophosphorylation activity in membranes kept at near 0 degrees C. Divalent cations were required during mechanical disruption and during assays for Photosystem II activity, with Ca2+ serving best. The rate of photophosphorylation was severely inhibited by Ca2+ during assays. Results suggest that best rates are achieved when photosynthetic membranes contain Ca2+ exposed to the interior surface, facilitating Photosystem II activity, and Mg2+ exposed to the exterior surface during assays, facilitating photophosphorylation activity.

Calcium↗
PubMed1978

Lead toxicity and phosphate deficiency in chlamydomonas.

The addition of lead salts to phosphate-containing Chlamydomonas reinhardtii media caused precipitation of Pb(3)(PO(4))(2), effectively removing phosphate from solution. The effect of Pb(2+) on growth of Chlamydomonas in liquid cultures depended strictly on the ratio of the equivalents of Pb(2+) to phosphate present. When the amount of Pb(2+) approached equivalency with phosphate, cell growth was initially slow as cells adhered to the surface of the precipitated Pb(3)(PO(4))(2). Later, cells grew at a normal rate, spread throughout the solution, and reached the same densities obtained in the absence of Pb(2+). Cells did not survive when the amount of Pb(2+) in the culture exceeded the equivalents of phosphate.Elemental analysis showed that in the presence of equivalent Pb(2+) and phosphate, considerable Pb(2+) remained in solution. The concentration of dissolved Pb(2+) did not vary significantly when the amount of Pb(2+) added to the culture was increased slightly, from an amount which permitted growth to an amount which completely prevented growth. The concentration of phosphate was decreased to an undetectable level when the amount of Pb(2+) approached equivalency with phosphate.In the presence of the chelating agent nitrilotriacetic acid, higher concentrations of Pb(2+) remained in phosphate-containing media. The chelated Pb(2+) did not retard the growth of Chlamydomonas.It appears that Pb(2+) is not toxic to Chlamydomonas, but kills cells by depriving them of phosphate.

Journal Article↗
PubMed1977

Cold Shock Syndrome in Anacystis nidulans.

The phenomenon of cold shock in Anacystis nidulans has been explored further in terms of loss of viability and immediate and subsequent metabolic effects. Cold shock was observed also in two closely related strains in which unsaturated fatty acid contents are also known to be low and temperature-dependent. Loss of viability was maximum for cells grown at temperatures above 40 C (<10(-4) survivors after 5 min at 0 C) but became negligibly small for cells grown below 34 C. Development of the cold-sensitive condition after transfer 25 --> 39 C was slow and comparable to rate of growth; development of the insensitive condition after transfer 39 --> 25 C was rapid, implying rapid in situ alteration. An immediate metabolic effect, observed as a decrease in rate of photosynthetic O(2) evolution measured at growth temperature, was less severe than loss of viability. Continued light incubation under growth conditions led to slow decay in rate of O(2) evolution accompanied by loss of membrane chlorophyll. The multiple effects which comprise the cold shock syndrome appear to be membrane-related phenomena and thereby provide an experimental probe of normal membrane function.

Journal Article↗
PubMed1977

Spectral Changes in Anacystis nidulans Induced by Chilling.

When Anacystis nidulans, strain TX 20 was grown at 39 C, then rapidly chilled to 0 C, a pigment with a carotenoid-like spectrum was bleached. This effect was not seen when cells which had been grown at 25 C were chilled. The effect seen in 39 C-grown cells was not reversible except under extreme conditions such as heating to near boiling for several minutes. Bleaching could be prevented by prior exposure of cells to glutaraldehyde, but could not be reversed by glutaraldehyde treatment following chilling. The effect occurred upon chilling 39 C-grown cells even after extensive heating at 85 C, a treatment which destroys phycocyanin and metabolic activities. 25 C-grown cells were induced to bleach by chilling when suspended in 50% glycerol. The results are interpreted as indicating a chill-induced change in aggregation state of a carotenoid, which changes its specific absorbance.

Journal Article↗
PubMed1975

Partial reactions of photosynthesis in briefly sonicated chlamydomonas: I. Cell breakage and electron transport activities.

The cell structure of Chlamydomonas reinhardi is disrupted by brief exposure to sonication. The extent of cell breakage can be determined quickly by cell count with the light microscope. Rates of photochemical activities of briefly sonicated cells approach those reported for higher plant chloroplasts. These activities are a sensitive function of time of sonication and sonic power used. The method of brief sonication is rapid and convenient and gives a stable preparation useful for determining photochemical activities in Chlamydomonas.

Journal Article↗
PubMed1975

Partial Reactions of Photosynthesis in Briefly Sonicated Chlamydomonas: II. Photophosphorylation Activities.

Briefly sonicated Chlamydomonas reinhardi cells are capable of both cyclic and noncyclic photophosphorylation and, in each case, the maximum rates approach those reported for higher plant chloroplasts. Photophosphorylation coupled to ferricyanide reduction occurs with a P/2e ratio approaching unity.The conditions for optimum activity are similar to those reported for spinach or swiss chard chloroplasts; the major difference is the extreme sensitivity to salt and relative insensitivity to methylamine. Cell preparation, sonication, and assays were all performed at room temperature under conditions suitable for screening a large number of potential mutants deficient in photophosphorylation activity. This method was easily adapted to Euglena gracilis strain Z but not adaptable for Chlorella vulgaris or Scenedesmus obliquus strain D(3).

Journal Article↗