E. Broda

Did respiration or photosynthesis come first

Abstract The similarity of the mechanisms in photosynthetic and in oxidative phosphorylation suggests a common origin (conversion hypothesis). It is proposed that an early form of electron flow with oxidative phosphorylation (“prerespiration”), to therminal electron acceptors available in a reducing biosphere, was supplemented by a photocatalyst capable of a redox reaction. In this way, cyclic photophosphorylation arose. Further stages in evolution were reverse electron flow, powered by ATP, to make NADH as a reductant for CO 2 , and subsequently noncyclic electron flow. These processes concomitantly provided the oxidants indispensable for full development of oxidative phosphorylation, i.e. for normal respiration: sulphate, O 2 , and, with participation of the nitrificants, nitrite and nitrate. Thus prerespiration preceded photosynthesis, and this preceded respiration. It is also suggested that nonredox photoprocesses of the Halobacterium type are not part of the mainstream of bioenergetic evolution. They do not lead to photoprocesses with electron flow.

Dependence of sulphate uptake by Anacystis nidulans on energy, on osmotic shock and on sulphate starvation

Sulphate uptake by Anacystic nidulans under aerobic conditions in the light was found to be sensitive to metabolic poisons, such as N, N′-dicyclohexyl-carbodiimide and carbonyl cyanide m-chlorophenyl hydrazone. It was also depressed by darkness. The sulphate absorption is an energy-dependent process. Sulphate uptake was also inhibited by chromate and selenate.Osmotic shock strongly affected sulphate uptake. This effect could be interpreted by a loss of a binding protein involved in the absorption of sulphate. Osmotic shock also depressed oxygen production in light and oxygen consumption in darkness; however, shocked cells were able to grow normally.Sulphate uptake was strongly enhanced by sulphate starvation, but this enhancement was partly prevented by chloramphenicol. Apparently sulphate starvation depressed the synthesis of a carrier involved in the transport of sulphate. During sulphate starvation the membrane potential, measured by the uptake of triphenylmethylphosphonium, increases. This may be due to changes in the membrane.

Die Zinkaufnahme in das Innere von Chlorella

SummaryThe uptake of labelled Zn by asynchronous Chlorella fusca was measured under conditions of optimum and minimum energy supply (light and air, or dark and nitrogen, respectively). Part of the Zn equilibrates rapidly with the medium, and soon after the uptake it can be washed out quickly with non-labelled Zn carrier solution; it is probably bound in the free space (cell wall). This component of the uptake is also observed with cells kept in minimum conditions, with dead cells and with isolated cell wall material.Under optimum conditions Zn is taken up strongly for long periods and cannot be washed out completely. The velocity of uptake depends on the Zn content of the cells, and follows saturation kinetics. The uptake has no influence on the efflux of preabsorbed Rb. The retained Zn is thought to be inside the cells. It may enter by way of a pump. However, an energy-independent path of entry, with a differnt temperature coefficient, is also observed. All uptake processes are influenced by Ca.Part of the labelled Zn is slowly removed from the interior of the cell on treatment with a solution of carrier Zn or EDTA. This loss does not depend on energy supply and may occur via the second pathway. Net loss of labelled Zn is also observed after the energy supply is turned off, without change of solution, but the loss can be compensated by a simultaneous increase in the external concentration of labelled Zn. The question is discussed whether the energy-dependent Zn uptake is an “active” process.

Untersuchung der Lichtabhängigkeit der Aufnahme von Rubidium, Zink, Kobalt, Blei und Cer durch Chlorella nach einer Flußmethode

A flow method for the measurement of the uptake of labelled substances by plant cells has been developed. Accumulation in the medium of substances released by the plants is thereby avoided, and a more precise determination of the rate of uptake-also of transients-than through the usual, static methods is possible. The time function of the stimulation of the uptake of Rb by Chlorella fusca by light at 30° has been analyzed, and the component believed to represent active transport separated from other components that have shorter time constants; at 3° the active component is much reduced.In the cases of the heavy metal ions Zn, Co, Pb and Ce, even after presaturation with the ions in the dark for the suppression of the short-term uptake the light-independent long-term uptake is far stronger than with Rb. Moreover, for Zn and Co the uptake is greatly stimulated by light at 30°, but little if at all at 5°. No stimulation was found under any conditions with Ce. With Pb, the light effect was hardly reproducible, and in any case extremely small. The energy-dependent transport of Zn and Co is probably active.SummaryA flow method for the measurement of the uptake of labelled substances by plant cells has been developed. Accumulation in the medium of substances released by the plants is thereby avoided, and a more precise determination of the rate of uptake—also of transients—than through the usual, static methods is possible. The time function of the stimulation of the uptake of Rb by Chlorella fusca by light at 30° has been analyzed, and the component believed to represent active transport separated from other components that have shorter time constants; at 3° the active component is much reduced.In the cases of the heavy metal ions Zn, Co, Pb and Ce, even after presaturation with the ions in the dark for the suppression of the short-term uptake the light-independent long-term uptake is far stronger than with Rb. Moreover, for Zn and Co the uptake is greatly stimulated by light at 30°, but little if at all at 5°. No stimulation was found under any conditions with Ce. With Pb, the light effect was hardly reproducible, and in any case extremely small. The energy-dependent transport of Zn and Co is probably active.

The evolution of bioenergetic processes

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Nitrogen fixation as evidence for the reducing nature of the early biosphere

Probably the first nitrogen fixers were anaerobic, non-photosynthetic, bacteria, i.e. fermenters. During the evolution of N2 fixation they still needed nitrogen on the oxidation level of ammonia. Because of the complexities in structure and function of nitrogenase this evolution must have required a long time. The photosynthetic and later the respiring bacteria inherited the capacity for N2 fixation from the fermenters, but the process did not change a great deal when it was taken over. Because of the long need for NH3, which is unstable in a redoxneutral atmosphere, a long-persisting reducing atmosphere was needed. The transition to a redoxneutral atmosphere, dominated by CO2, H2O and N2, cannot have been rapid, and the NH3 in it was recycled. Probably the atmosphere contained for a long time, as was suggested by Urey but is often denied now, a great deal of methane as a reductant. The recycling occurred with participation of intermediates like cyanide, through energy input as UV radiation or as electric discharges. A stationary state was set up. The hypothesis is recalled that coloured, photosynthetic, NH3 bacteria, analogous to coloured sulphur bacteria, may have existed, or may still exist, in reducing conditions. A few remarks are made about the origin of nitrification in the later, oxidizing atmosphere.

Das Verhalten von Chlorella fusca gegenüber Perchlorat und Chlorat

SummaryThe reactions of labelled chlorate and perchlorate with Chlorella fusca have been studied. Independently of conditions, perchlorate is absorbed only to a small extent, and it is not reduced to chloride. In contrast, chlorate is reduced with Michaelis-Menten kinetics. The velocity of reduction is higher in the light than in the dark, and is depressed by DNP, cyanide and iodoacetate. The reduction of chlorate is competitively inhibited by nitrate and nitrite. Apparently uptake and reduction of chlorate are mediated by mechanisms evolved for nitrate and nitrite metabolism. Chlorella grown on ammonium as the only nitrogen source at first does not reduce chlorate. The velocity of reduction in the dark by nitrate-grown Chlorella is enhanced by a period without nitrogen before the test.ZusammenfassungDas Verhalten von Chlorella fusca gegenüber markiertem Chlorat und Perchlorat wurde untersucht. Unabhängig von den Bedingungen wird Perchlorat nur zu einem geringen Maß aufgenommen, und es wird nicht zu Chlorid reduziert. Dagegen wird Chlorat mit Michaelis-Menten-Kinetik reduziert. Die Geschwindigkeit wird durch Belichtung erhöht und durch DNP, Cyanid und Jodacetat vermindert. Die Reduktion des Chlorats wird durch Nitrat und Nitrit kompetitiv gehemmt. Offenbar erfolgen Aufnahme und Reduktion von Chlorat durch Mechanismen, die dem Stoffwechsel von Nitrat und Nitrit dienen. Nach Züchtung auf Ammonium als einziger Stickstoffquelle reduziert Chlorella anfangs Chlorat nicht. Die Dunkelreduktion durch nitratgezüchtete Chlorella wird durch eine stickstofffreie Vorperiode beschleunigt.

Die Dissoziation von Permanganation durch lokale Energiezufuhr

Die Moglichkeit der lokalen Energiezufuhr zu bestimmten Atomen durch Atomkernreaktionen wird aufgezeigt. Die Anregung von Permanganation mit Energien der Grosenordnung 1000 kcal durch Beschiesung mit langsamen Neutronen und Einfang der Neutronen durch Mn (Szilard-Chalmers-Effekt) wird experimentell durchgefuhrt. Das entstehende Radio-Mn (Mn*) liegt nach Ende der Bestrahlung teils als Mn*Oa, teils als Mn*O4− vor. Die Untersuchung der Abhangigkeit des Verteilungsverhaltnisses (“Retention”) von den Versuchsbedingungen (Neutronenenergie, pH-Wert, Aggregatzustand, Konzentration, Temperatur, Anwesenheit von Fremdionen in Losung oder in einem Mischkristall) fuhrt im Einklang mit einer HypotheseLibbys zu dem Ergebnis, das bei der Zerstorung des Anions Mn*O4− (Primarprozes) keine Reduktion des Mn* mit Abdissoziation von Sauerstoffatomen, sondern eine Abdissoziation von Sauerstoffionen unter Hinterlassung eines Kations stattfindet. Das instabile Kation des Typus Mn*O3+ verliert bald die im Primarprozes erworbene kinetische Energie und setzt sich in einem “thermischen” Sekundarprozes mit Molekulen des Mediums zu Mn*O2 oder Mn*C4− um. Diese chemische Stabilisierung der Primarprodukte verlauft innerhalb unmesbar kurzer Zeit, wenn Losungen bestrahlt werden, jedoch mit mesbarer temperaturabhangiger Geschwindigkeit, wenn die Primarprodukte in einem Kristallgitter eingeklemmt sind. Die Stabilisierungsreaktionen werden diskutiert.

Die energieabhängige Aufnahme von Thallium durch Chlorella

SummaryThe uptake of labelled thallous ion into the interior of Chlorella fusca is enhanced by light. This is ascribed to active transport by way of the K (and Rb) pump. The Michaelis constants differ between the higher and the lower concentration ranges, but they are similar for Rb and Tl.The additional, rapid, light-independent adsorption of Tl, mainly by the cell wall, is stronger than that of the alkali ions, but weaker than that of divalent cations. The adsorbed Tl is subject to elution by complexing agents (probably mainly glycolic acid) secreted by the cells, especially in the light.In spite of the similarity of the Michaelis constants, the inhibition of the light-dependent uptake of labelled Rb by unlabelled Tl is far stronger than the inhibition of Tl uptake by Rb. The efficiency of Tl may be due to double action: namely, competition with Rb for the carrier and negative influence on a transport ATPase.The uptake of labelled thallous ion into the interior of Chlorella fusca is enhanced by light. This is ascribed to active transport by way of the K (and Rb) pump. The Michaelis constants differ between the higher and the lower concentration ranges, but they are similar for Rb and Tl.The additional, rapid, light-independent adsorption of Tl, mainly by the cell wall, is stronger than that of the alkali ions, but weaker than that of divalent cations. The adsorbed Tl is subject to elution by complexing agents (probably mainly glycolic acid) secreted by the cells, especially in the light.In spite of the similarity of the Michaelis constants, the inhibition of the light-dependent uptake of labelled Rb by unlabelled Tl is far stronger than the inhibition of Tl uptake by Rb. The efficiency of Tl may be due to double action: namely, competition with Rb for the carrier and negative influence on a transport ATPase.

Mechanismen der Aufnahme von Zink durch Bäckerhefe

The uptake of labelled Zn by bakers yeast after exhaustion of the intracellular substrates for energy metabolism has been investigated. Without addition of glucose (substrate), equilibrium is reached rapidly. Binding of Zn is attributed to cell wall components. The amount bound approaches a saturation value at a Zn concentration in solution of the order of 10(-2) M. Initially, the Zn is bound reversibly, but it gradually changes into a firmly bound form. Substrate-independently, killed cells bind more Zn than living cells; apparently more binding sites become accessible. After addition of substrate, however, living cells take up additional Zn irreversibly over long periods. It is suggested that the Zn absorbed substrate-dependently enters the interior of the cell. The process does not depend strongly on the presence of air. It follows Michaelis-Menten kinetics, and the temperature coefficients (Q 10), at different concentrations and temperatures, are 2-2,7. No efflux of Zn from the interior of the cell is observed. Reasons are given for considering the substrate-dependent uptake of Zn as an active process.SummaryThe uptake of labelled Zn by bakers yeast after exhaustion of the intracellular substrates for energy metabolism has been investigated. Without addition of glucose (substrate), equilibrium is reached rapidly. Binding of Zn is attributed to cell wall components. The amount bound approaches a saturation value at a Zn concentration in solution of the order of 10-2 M. Initially, the Zn is bound reversibly, but it gradually changes into a firmly bound form. Substrate-independently, killed cells bind more Zn than living cells; apparently more binding sites become accessible. After addition of substrate, however, living cells take up additional Zn irreversibly over long periods. It is suggested that the Zn absorbed substrate-dependently enters the interior of the cell. The process does not depend strongly on the presence of air. It follows Michaelis-Menten kinetics, and the temperature coefficients (Q10), at different concentrations and temperatures, are 2–2,7. No efflux of Zn from the interior of the cell is observed. Reasons are given for considering the substrate-dependent uptake of Zn as an active process.