Properties of ATP-induced chlorophyll luminescence in chloroplasts.

1. The recently described reaction of ATP-induced luminescence is analyzed for its relation to other ATP-induced reactions such as ATP-driven transmembrane proton gradient formation and ATP-driven reverse electron flow. 2. In the absence of phenazine methosulfate ATP-induced luminescence is optimal while the main phase of ATP-driven reverse electron flow is eliminated. 3. DCMU which by itself causes a much smaller luminescence, inhibits the ATP-induced luminescence. 4. Nigericin plus valinomycin, but not each by itself, fully inhibit the ATP-induced luminescence. 5. The observations are interpreted as indicating that ATP stimulates luminescence by a 2-fold mechanism: (a) increasing the amount of the reducing primary electron acceptor of Photosystem II, Q, and (b) creating a transmembrane electrochemical potential which serves to decrease the activation energy required for the charge recombination reaction which leads to luminescence.     

The diffusional water permeability in the halotolerant alga Dunaliella as measured by nuclear magnetic resonance

T₁ nuclear relaxation measurements of ¹H and ¹⁷O of water have been applied to study the kinetics of the diffusional transport of water across the cytoplasmic cell membrane of Dunaliella salina and Dunaliella bardawil. The water permeability coefficients at 25°C were found to be 1.5·10⁻³ cm/s and 1.8·10⁻³ cm/s, respectively, with an activation energy of 3.7 kcal/mol. The results indicate that the cell membrane of Dunaliella exhibits high diffusional permeability to water, similar in magnitude to that found for other cells and model membranes, and a relatively low activation energy. This regularity is in contrast to the exceptionally low glycerol permeability of the membrane (Brown, F.F., Sussman, I., Avron, M. and Degani, H. (1982) Biochim. Biophys. Acta 690, 165–173).     

NMR studies of glycerol permeability in lipid vesicles, erythrocytes and the alga Dunaliella

Glycerol diffusional permeabilities through the cytoplasmic cell membrane of Dunaliella salina, the cell envelope of pig erythrocyte and egg phosphattidylcholine vesicles were measured by NMR spectroscopy employing the spin-echo method and nuclear T₁ relaxation. The following permeability coefficients (P) and corresponding enthalpies of activation (ΔH^‡) were determined for glycerol at 25°C: for phosphatidylcholine vesicles 5·10⁻⁶ cm/s and 11±2 kcal/mol; for pig erythrocytes 7·10⁻⁸ cm/s and 18±3 kcal/mol, respectively; for the cytoplasmic membrane of D. salina the permeability at 17°C was found to be exceptionally low and only a lower limit (P<5·10⁻¹¹cm/s) could be calculated. At temperatures above 50°C a change in membrane permeability occurred leading to rapid leakage of glycerol accompanied by cell death. The data reinforce the notion that the cytoplasmic membrane of Dunaliella represents a genuine anomaly in its exceptional low permeability to glycerol.     

Analysis of light-induced proton uptake in isolated chloroplasts

1. 1. A simple kinetic analysis of light-induced proton uptake into chloroplasts is presented. It is derived from a model of the reaction in which the incoming proton is obligatorily bound by an intra-chloroplast component, and allows quantitative analysis of the effect into parameters of light and dark rate constants and the availability of the chloroplast component.

2. 2. The effect of the following agents on the derived parameters has been measured: electron and energy transfer inhibitors, uncouplers, NaCl concentration, light intensity and pH.

3. 3. A maximal ratio of 4 protons taken up per electron transported has been observed, using ferricyanide as an electron acceptor.

4. 4. A stimulation of light-induced proton uptake by phosphate or arsenate, ADP and Mg has been observed. It was not sensitive to concentrations of Dio-9, which eliminated ATP synthesis.

5. 5. The results are seen as inconsistent with the chemiosmotic theory of energy coupling as presently presented. It is suggested that they may be interpreted in terms of a model in which the function of the proton pump is to enable co-transport into the chloroplasts of the negatively charged complex of phosphate, ADP and Mg.