Determination of the light pathlength elongation in leaves by measuring P700 quantitatively.

P700 absorption change signals were measured at 800 nm for plant leaves and plant leaf extracts by illuminating with far-red light. The ratio of the signal amplitudes for the two sample types shows the degree of optical signal intensification. The intensification is due to optical path-length elongation, itself caused by scattering. The intensification was found to be between 6 and 15 for different leaves. For spinach leaves, the intensification varied less than 10% among samples. By replacing the air in the spongy layer of a leaf with an isotonic solution it was shown that nearly half of the intensification is due to the scattering at air-tissue interfaces. The comparison of the P700 signals of a leaf with its extract would seem to be a new technique for determining the optical scattering effects of leaves.

Reaction sequences from light absorption to the cleavage of water in photosynthesis : Routes, rates and intermediates.

The reaction sequence between the primary electron acceptor, the oxidized Chlorophyll-aII, and the terminal electron donor, the water splitting enzyme system S, is being described in the range from nanoseconds to milliseconds. For the cleavage of water Chlorophyll-aII (+) extracts four electrons in four turnovers from the enzyme system S responsible for the water oxidation. For each extraction the electron is moved step by step along the chain that connects the Chlorophyll-aII center with that of S. Beginning with the transfer from the immediate donor, D1, to Chl-aII (+), the subsequent transfer from D2 to D1 (+) ends in the electron transfer from S to D2 (+). This final act establishes in S the oxidizing equivalent, probably in the form of oxidized manganese. Coupled with these acts is an intrinsic proton release and a surplus charge formation. After the generation of the 4th oxidizing equivalent in a concerted final action the evolution of O2 from water takes place. Correlations between the events are described quantitatively.

Total recovery of O2 evolution and nanosecond reduction kinetics of chlorophyll-a II (+) (P-680 (+)) after inhibition of water cleavage with acetate.

Oxygen evolution and reduction kinetics of the photooxidized Chl-aII (+) have been measured in oxygen-evolving complexes from the thermophilic cyanobacterium Synechococcus sp. 1. Incubation of PS II particles with acetate resulted in an inhibition of oxygen evolution and a retardation of the Chl-aII (+)=reduction kinetics from the nanosecond range to the microsecond range, indicating a modification of the donor side of photosystem II (PS II). 2. After the first two flashes given to a dark-adapted, acetate treated sample, Chl-aII (+) was re-reduced with a half-life time of 160 µs by a component of the donor side of PS II. Under repetitive excitation Chl-aII (+) was re-reduced in 500 µs by electron back reaction from the primary acceptor QA (-) (X-320(-)). Obviously, in the presence of acetate only two electrons are available from the donor side. 3. Both oxygen evolution and nanosecond reduction kinetics of Chl-aII (+) were restored to the control level when acetate was removed. 4. The results indicate a tight coupling between O2 evolution and nanosecond reduction kinetics of Chl-aII (+). 5. The reversible inhibition is probably due to a replacement of Cl(-) by acetate within the water splitting enzyme. 6. Due to its strongly retarded kinetics, the reversibly modified system may facilitate investigations of the mechanism of the donor side.

Calcium-ion catalysed nonenzymatic ATP synthesis from ADP and carbamylphosphate.

Incubation of aqueous Ca2+, carbamylphosphate and ADP results in ATP formation with yields up to 20%. The dependence of the yield on the reaction parameters suggests that this transphosphorylation reaction proceeds heterogeneously on the surface of the calcium-carbamylphosphate precipitate.

[All-or-none behaviour and bistability in a simple cell model with autocatalysis of type A+2B = 3B (author's transl)]. / Alles-oder-nichts Verhalten und Bistabilität in einem einfachen Zellmodell mit Autokatalyse vom Typ A+2B = 3B.

Nonlinear kinetics in a chemical cell model involving only one substrate (A) and one product (B), two reactions (A yields B and A + 2B yields OB), and passive diffusion of A and B through the cell wall, can exhibit complex behaviour including oscillations, bistability (switching) and spiking. One such system is presented, which shows three kinds of response as depending on the quantity of a stimulus--a sudden imput of product B: i. no response; ii, spiking; iii, switching into an alternative steady state--i.e. an "all-or flip-or-none" response.