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E Broda

Publications and source records attributed to E Broda.

16 recordsLinked to original sources
PubMed1979

Model experiments on nitrite and nitrate in simulated primeval conditions.

In experiments on the prebiotic formation of nitric oxides, anoxic mixtures of N2 and water vapour were sparked in contact with phosphate buffer solutions at various pH values. Nitrite was found in the aqueous phase, and nitrate grew from it, presumably by reaction with H2O2. In acid solutions, these anions were reduced and destroyed by Fe2+, and the same was true of nitrite in solutions kept at a pH value similar to that of the contemporary ocean (8.2) with HEPES buffer. Nitrate was not destroyed in short-term experiments, but as in sparking nitrate is formed only vianitrite, neither anion could accumulate. In further sparking experiments with alkaline sulphide, both nitrite and nitrate were reduced entirely. It is concluded that it is unlikely that the primeval ocean contained appreciable concentrations of nitrite or nitrate either at the reducing or at the redox-neutral stage.

Anaerobiosis↗
PubMed1978

[Uptake of labeled zinc by Chlorella containing different amounts of zinc].

Chlorella fusca was grown asynchronously for 2 weeks in media with different Zn concentrations up to 10(-3) M. Growth was optimal at 10(-5) M Zn. The Zn contents of the algae were followed by activation analysis. They increased with increasing Zn concentration in the media, and, except with the lowest Zn concentrations, with time. Further, the uptake of labelled Zn (65Zn) from 5 . 10(-6) M solution by cells of known Zn content was measured at 30 degrees C during one day in minimum and optimum conditions (dark/nitrogen or light/air, respectively). The rate of uptake showed a maximum with algae grown in a medium with 10(-5) M Zn. However, algae exposed to a lethal Zn concentration (10(-3) M) also absorbed much Zn; this anomalous uptake is ascribed to a breakdown of the cell membrane as a permeability barrier.

Cell Membrane Permeability↗
PubMed1977

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

Sulphate uptake by Anacystis nidulans under aerobic conditions in the light was found to be sensitive to metabolic poisons, such as N,N'-dicyclohexylcarbodiimide 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.

Aerobiosis↗
PubMed1977

Two kinds of lithotrophs missing in nature.

Two groups of lithotrophic bacteria, the existence of which may be expected on evolutionary and thermodynamical grounds, have not yet been detected: (A) photosynthetic, anaerobic, ammonia bacteria, analogous to coloured sulphur bacteria, and (B) chemosynthetic bacteria that oxidize ammonia to nitrogen with O2 or nitrate as oxidant.

Ammonia↗
PubMed1977

The length of the transition period from the reducing to the neutral biosphere.

The development of the complicated mechanisms for N2 fixation, which in nature is an endergonic process and requires a great deal of ATP, must have taken a long time. During that time primeval NH3 must still, albeit to a decreasing extent, have been available as a source of nitrogen. This is true, whether N2 fixation originally arose in the primitive anaerobes, or, according to Postgate, in more advanced bacteria. As NH3 resists UV radiation only in the presence of excess H2 it follows that the disappearance of H2 and the transition from the reducing to the neutral biosphere also took a long time, probably of the order of 10(9) degrees yr. According to previous evidence, the transition from the neutral to the oxidizing biosphere likewise took long; this length enabled the organisms to adapt the N2 fixing machinery to aerobic conditions.

Adenosine Triphosphate↗
PubMed1977

The position of nitrate respiration in evolution.

Egami's hypothesis that oxygen respiration evolved from nitrate respiration, and this from nitrate fermentation, is not accepted. The reasons are: (1) Presumably there was no nitrate before O2 in the biosphere. (2) On mechanistic grounds, respiration (oxidative phosphorylation) is to be derived directly from photosynthesis (photosynthetic phosphorylation) rather than from any form of fermentation.

Biological Evolution↗
PubMed1977

[Uptake of zinc by synchronous cells of Chlorella fusca].

The uptake of labelled zinc into the interior of synchronous Chlorella fusca was measured at 30 degrees C in minimal and optimal conditions (dark/nitrogen or light/air, respectively). No saturation with Zn was reached during 10 hours. Uptake strongly depended on the stage of the cells during the development cycle. The rates of uptake per unit cell number, per unit cell volume and also per unit cell surface, reach maxima be forecell division, and thereafter strongly decrease. Clearly the transport system is built up during cell growth. The similarity of the dependence of the rates of uptake in minimal and optimal conditions on the stage of development suggests identity of the transport systems.

Cell Cycle↗
PubMed1975

The history of inorganic nitrogen in the biosphere.

When in the primeval atmosphere ammonia approached exhaustion, bacteria resembling clostridia developed mechanisms for nitrogen fixation. The fixation was continued by the photosynthetic bacteria. In the later, oxidizing, atmosphere the combined activities of the nitrificants and the denitrificants could lead to a large-scale cyclic regeneration of free nitrogen. The possibility of a descent of the nitrificants from hypothetical photosynthetic bacteria, which used ammonia as electron donor, is discussed. The anoxygenic atmosphere contained no nitrate, and therefore neither nitrate fermentation nor nitrate respiration were precursors of aerobic respiration. This evolved from photosynthesis. In nitrate fermentation, nitrate serves only as an incidental electron acceptor; this process is merely an evolutionary sideline. Nitrate respiration evolved from aerobic respiration. While in present conditions the reaction of nitrogen with oxygen and water to give nitrate is exergonic and possibly occurs at a low rate, the antagonistic action of the denitrificants maintains the stationary concentrations of nitrogen and oxygen in the air.

Aerobiosis↗
PubMedDate not supplied

The begginning of photosynthesis.

There is no evolutionary continuity between photochemical abiosynthesis and bacterial photosynthesis. Rather, the photosynthetic bacteria are descendants of fermenters that did not use light. Photosynthesis and respiration, both using electron flow coupled with phosphorylation, have a common origin ('conversion hypothesis'), but photosynthesis came first. Anaerobic (nitrate or sulphate) respiration cannot have preceded photosynthesis as neither nitrate nor sulphate existed on the early earth. Sulphate was made first by photosynthetic sulphur bacteria. Nitrate arose even later, namely, in the aerobic biosphere produced by the blue-green algae, the first 'phytotrophs'. Photophosphorylation may have originated through the combination with membrane function of substrate level phosphorylation in reactionsand function of substrate level phosphorylation in reactions of photoproducts. Cyclic photophosphorylation arose while the biosphere was still reducing. It was supplemented later by processes for the light-based production of reducing power (NADH), ATP-powered electron flow, and subsequently light-powered electron flow with ATP production (noncyclic photophosphoryaltion). These later processes served the assimilation of CO2.

Adenosine Triphosphate↗
PubMedDate not supplied

[Influence of twovalent foreign cations on the uptake of zinc by Chlorella (author's transl)].

The influence of 10(-4) divalent cations on the uptake of labelled Zn in the concentration range 10(-5) to 5 x 10(-5) M into the interior of Chlorella fusca at 30 degrees C was measured during 75 min. The Zn absorbed on the surface or contained in the free space was removed by washing with EDTA. Corrections were applied for the loss in concentration due to surface adsorption, etc. The results were consistent with competitive inhibition of Zn uptake by the foreign ions. No allosteric inhibition was found. From the Lineweaver-Burk diagram, for uninhibited Zn, KM was found as 7 x 10(-6) M and Vmax as 8.3 x 10(-9) mol.min-1.g-1 algae. The inhibitor constants were: Mg 1.3 x 10(-5), Ca 4.3 x 10(-5), Co 4.3 x 10(-5), Ni 4.3 x 10(-5), Cd 1.3 x 10(-5) and Pb 9.4 x 10(-7) M. The values given for Km and the inhibitor constant refer to the velocities of uptake after 45 min.

Biological Transport↗