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C Giersch

Publications and source records attributed to C Giersch.

24 records · Page 2Linked to original sources
PubMed1980

Energy charge, phosphorylation potential and proton motive force in chloroplasts.

Adenylate concentrations were measured in intact chloroplasts under a variety of conditions. Energy charge was significant in the dark and increased in the light, but remained far below values expected from observed phosphorylation potentials in broken chloroplasts, which were 80 000 M-1 or more in the light. With nitrite as electron acceptor, phosphorylation potentials in intact chloroplasts were about 80 M-1 in the dark and only 300 M-1 in the light. Similar phosphorylation potentials were observed, when oxaloacetate, phosphoglycerate or bicarbonate were used as substrates. delta G'ATP was -42 kJ/mol in darkened intact chloroplasts, -46 kJ/mol in illuminated intact chloroplasts and -60 kJ/mol in illuminated broken chloroplasts. Uncoupling by NH4Cl, which stimulated electron transport to nitrite or oxaloacetate and decreased the proton gradient, failed to decrease the phosphorylation potential of intact chloroplasts. Also, it did not increase the quantum requirement of CO2 reduction. It is concluded that the proton motive force as conventionally measured and phosphorylation potentials are far from equilibrium in intact chloroplasts. The insensitivity of CO2 reduction and of the phosphorylation potential to a decrease in the proton motive force suggests that intact chloroplasts are over-energized even under low intensity illumination. However, such a conclusion is at variance with available data on the magnitude of the proton motive force.

Adenosine Diphosphate↗
PubMed1977

CO2 reduction by intact chloroplasts under a diminished proton gradient.

9-Aminoacridine has been used to monitor the intrathylakoid pH of photosynthetically competent intact chloroplasts. Values obtained from 9-aminoacridine accumulation in the chloroplasts must be corrected for light-dependent binding of 9-aminoacridine to the thylakoid membranes. During nitrite reduction by intact chloroplasts, the intrathylakoid proton concentration increased. It decreased somewhat during CO2 reduction. However, low concentrations of uncoupling amines such as NH3 or cyclohexylamine, which rapidly penetrated the chloroplast envelope and decreased the intrathylakoid proton concentration, failed to reduce, and actually stimulated, rates of CO2-dependent oxygen evolution even under rate-limiting light. In contrast, low concentrations of carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) OR NIGERICIN, WHICH INHIBITED CO2 reduction, even appeared to increase the intrathylakoid proton concentration. As indicated by measurements of the 515 nm signal of the chloroplasts, the light-induced membrane potential was not much affected by low concentrations of the uncoupling amines, but was decreased by FCCP and by high concentrations of the amines. Even in the presence of high concentrations of NH4C1, ATP/ADP ratios of illuminated chloroplasts remained far above the ratios observed in the dark. In contrast, low concentrations of FCCP were sufficient to reduce ATP/ADP ratios to the dark value even under high intensity illumination. The observations are difficult to explain within the framework of the chemiosmotic hypothesis as presently discussed.

Acridines↗
PubMed1975

The response of oscillating glycolysis to perturbations in the NADH/NAD system: a comparison between experiments and a computer model.

The glycolytic pathway is described by a set of coupled non linear differential equations of first order with respect to time. The individual terms of these equations consist of enzyme velocities assuming a steady state hypothesis for the enzymatic forms. These are specified and the system is solved numerically. Oscillations are explained by interaction of PFK with the adenylate system. The conditions for the occurrence of oscillations are tested in a series of computer runs. The phase relations between intermediates of the model agree with those found in yeast cells. As an application of the model the disturbation of oscillations by the addition of acetaldehyde is simulated. The predictions of the model agree with experimental results.

Acetaldehyde↗
PubMedDate not supplied

The oscillatory network of glycolysis: a model for multiple phase output derived from a single master oscillator.

In oscillatory glycolysing yeast cells the reaction rates of 11 enzymic steps are almost completely in phase whereas the concentrations of intermediates fluctuate with highly different phases. Metabolite concentrations depend on the amplitudes of reaction rates even more than on their phases. In this way almost, synchronized enzymes can given rise to a variety of phases, resembling a "master oscillatory" which controls a series of peripheric event with different phases.

Adenine Nucleotides↗