Kinetics of Proton‐Transport‐Coupled ATP Synthesis in Chloroplasts. Activation of the ATPase by an Artificially Generated ΔpH and Δψ

1991

FEBS Letters

Self Cite

The H+-ATPase from chloroplasts was brought into the active, reduced state. Then, an electrochemica| potential difference of protons across the thylakoid membranes was F_,cnerated b~ ,in acid-base transition, ~lpH, combined with a K*/valinomycin diffusion potential. ~. The initial rate of ATP synthesis was measured with a rapid-mixing quenched-flow apparatus in the time-range between 20-150 ms. The rate of ATP symhesis depends in a sigmoidal way on ,dpH. Increasing diffusion potentials shifts the ApH-dcpendcncies to ~ower ~pH values. Analysis of the data indicate that the rate of ATP synthesss depends on the electrochemical potential diffcrenoe of protons irrespective of the relative contribution of ApH and Ch!oroplast; H~-ATPase; Enzyme-kinetics

Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

“…Short reaction times (20-I 50 ms) were achieved with a rapid-mixing quenched-flow system (Durrum D 133) as described earlier [5]. ATP was measured by luciferin/luciferase [5].…”

Section: Methodsmentioning

confidence: 99%

“…With ~ calculated from the Goldman equation as described in [5], and the experimental zapH, the electrochemical potential difference of protons, 4t~R +, is calculated. The data from Fig.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The rate of ATP‐synthesis as a function of ΔpH and Δψ catalyzed by the active, reduced H⁺‐ATPase from chloroplasts

Junesch

1991

FEBS Letters

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Kinetics of Proton‐Transport‐Coupled ATP Synthesis Catalyzed by the Chloroplast ATP Synthase

Ber Bunsenges Phys Chem

Fromme

Junesch

et al. 1986

& Varshavsky (1984) found three conserved sites per repeat. These sites could play a role in the molecular organization of satellites such as in nucleosome-positioning, i.e. in the formation of higher order chromatin structures. However, these effects have, if any, little to do with functions in an evolutionary sense (see Maynard Smith's (1982) discussion of this problem). ConclusionsThe picture on the evolutionary accumulation of satellite DNA emerging from the present analysis is thus as follows. Accumulation of HRDNA clusters in higher organisms is possible even if these sequences are of no functional significance or slightly deleterious. The occurrence of long stretches of satellite DNA can most readily be explained as a consequence of synergistic effects of several inherent molecular forces and natural selection. Satellite DNA is located preferentially in the neighbourhood of centromeres and telomeres, due to these structures having been selected for restricted rates of crossing over. The HRDNA sequences which accumulate are subject to certain constraints with respect to sequence composition. Constraints are imposed by the molecular self-organization of these sequences rather than by a possible functional role. To conclude, the production of HRDNA due to errors in replication and its accumulation during evolution do not provide a case against the well grounded assumption that biological systems operate at or close to their optimum efficiency. This is because there are forces that are very effective at stemming the amplification of sequences when required. Due to the control mechanisms showing nonlinear characteristics, the organization of satellite DNAs in the chromosomes is such that they cannot interfere with functions that are lively for the organisms.I want to thank Prof. Jurgen Brickmann for his valuable suggestions for improving the presentation, and Dr. Charles H. Langley for drawing Lewontin's paradox to my attention. References[I] R. Biophysical Chemistry 1 Catalysis / Chemical Kinetics J MembranesThe kinetics of proton-transport-coupled ATP synthesis catalyzed by the chloroplast ATPase (ATP synthase) was investigated after energization of the membrane by an artificially generated ApH and an electric potential difference, Ay. With a rapid mixing system, ATP synthesis was studied at short reaction times (<200 ms) where all relevant parameters (pH,,,, pHin, Ay, substrate and product concentrations) remain practically constant at their initial values. The reaction is investigated at three levels of complexity. (1) The ATPase is embedded in the natural membrane. (2) The ATPase is isolated, purified and reconstituted into asolectin liposomes. (3) The reconstituted ATPase is investigated under single site, single turnover conditions. The following results were obtained:Bcr. Bunsenges. Phys. Chem. 90, 1034-1040 (1986) -0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1986. 0005-9021/~6/1111--10~4 x 03 w n

Electric Field‐Driven ATP Synthesis Catalyzed by the Membrane‐Bound ATP‐Synthase from Chloroplasts

Bauermeister

Schlodder

Ber Bunsenges Phys Chem

1988

Self Cite

When chloroplast vesicles, suspended in a conducting aqueous medium, are exposed to an external electric field pulse, the membranebound ATP-synthase can catalyze ATP synthesis similar to energization of the membrane by light pulses. Inhibitors which bind to the enzyme inhibit light-induced ATP synthesis and external field-induced ATP synthesis at the same concentration. With uncouplers, which increase the ion permeability of the membrane, a higher concentration is necessary to inhibit electric field-induced ATP synthesis. This is due to the faster charging of the membrane capacity by an external electric field. The enzyme can exist in an oxidized and a reduced state. Both forms can catalyze field driven ATP synthesis, and the rates depend in a sigmoidal way on the field strength. For the same rate of ATP synthesis, the reduced form requires a lower field strength than the oxidized form.