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Summary The radiosensitizing effect of a rifamycin derivate — dimethylbenzyldesmethylrifampicin (DMB) was compared with that of actinomycin D in unicellular blue-green alga, Anacystis nidulans . These agents are active when added after irradiation and potentiate γ-ray-induced killing in cells. Pre-irradiation treatment of cells with DMB or actinomycin D is ineffective. DMB, which is strong inhibitor of RNA-directed DNA polymerase, greatly decreased the survival of irradiated A. nidulans cells compared to actinomycin D. This phenomenon of post-irradiation sensitization by DMB is probably a result of inhibition of reverse transcription process in the blue-green algae.

The blue-green algae appear to have maintained efficient repair systems. They were sensitized to gamma-irradiation by chemical sensitizers. This work presents evidence for the influence of sensitizers on post-irradiation DNA degradation. Uracil- 14 C labelled A. nidulans were irradiated in the presence of solutions of various radiosensitizers. Loss of radioactivity from the acid-precipitable DNA was used as a measure of DNA breakdown. Iodoacetic acid, p-chloromercuribenzoate, indanetrione, methylhydrazine and iodobenzoic acid were used at optimum concentrations for sensitization (cell survival). Four sensitizers, iodoacetic acid (3 × 10 −4 m ), indanetrione (10 −4 m ), methylhydrazine (10 −4 m ) and iodobenzoic acid (2 × 10 −4 m ) almost completely inhibited post-irradiation breakdown, but p-chloromercuribenzoate (10 −5 m ) had only a slight inhibitory effect. It was concluded that for this alga, DNA degradation could be affected by various sensitizers.

The polymerization of nitroethylene in dimethylformamide and tetrahydrofuran was studied in a wide temperature range. Pyridine and 3-methyl-4-ethyl-pyridine were used as catalysts. Polymerization was followed by adiabatic temperature rise as well as gravimetrically. At low temperatures the kinetics are first order with respect to catalyst and monomer. The degree of polymerization (at −75°C. in dimethylformamide and at −104°C. in tetrahydrofuran) is proportional to the degree of conversion. High molecular weight polymers are formed with intrinsic viscosities of the order of 2. In the intermediate temperature range (about −30°C.) the rate of reaction in dimethylformamide may be expressed by: At room temperature (0–25°C.), the kinetics are second order with respect to monomer in both solvents. The apparent activation energy is negative and low molecular weight polymers are obtained. The following mechanism is suggested in order to explain the experimental findings: The interaction of catalyst and monomer produces an active dipolar adduct, and the chain is propagated by a polar mechanism. The termination of the growing chain may take place spontaneously or by transfer of the catalyst to monomer. The activation energies associated with termination reactions are much higher than Ei and Ep, therefore at low temperatures the rates of both termination and transfer are approaching zero, while those of initiation and propagation are much less affected. At a sufficiently low temperature, which depends upon the dielectric constant of the solvent, the formation of “living” polymer is postulated. Die Polymerisation von Nitroathylen in Dimethylformamid und Tetrahydrofuran wurde in einem grosen Temperaturbereich untersucht. Als Katalysatoren dienten Pyridin und 3-Methyl-4-athyl-pyridin. Der Polymerisationsverlauf wurde sowohl mittels der adiabatischen Temperaturerhohungen als auch gravimetrisch verfolgt. Bei niederen Temperaturen verlauft die Reaktion nach 1. Ordnung in bezug auf Katalysator und Monomeres. Der Polymerisationsgrad (bei −75°C in Dimethylformamid und bei −104°C in Tetrahydrofuran) ist proportional dem Grad der Umsetzung. Polymere hohen Molekulargewichtes werden gebildet mit Intrinsic-Viskositaten in der Grosenordnung von 2. Im mittleren Temperaturbereich (ungefahr bei −30°C) kann die Reaktionsgeschwindigkeit in Dimethylformamid folgendermasen ausgedruckt werden: Bei Zimmertemperatur (0–25°C) sind in beiden Losungsmitteln die Reaktionen 2. Ordnung in bezug auf das Monomere. Die scheinbare Aktivierungsenergie ist negativ, und es werden Polymere niederen Molekulargewichtes erhalten. Folgender Reaktionsmechanismus wird zur Erklarung der experimentellen Ergebnisse vorgeschlagen: Die Wechselwirkung zwischen Katalysator und Monomerem erzeugt ein aktives dipolares Addukt, und die Kette wachst durch einen polaren Mechanismus. Der Abbruch der wachsenden Kette kann spontan oder durch Ubertragung mit dem Monomeren stattfinden. Die Aktivierungsenergien der Abbruchsreaktionen sind viel hoher als Ei und Ep. Deshalb nahern sich bei niederen Temperaturen die Geschwindigkeiten sowohl des Abbruchs als auch der Ubertragung Null, wahrend jene der Start- und Wachstumsreaktion viel weniger beeinflust werden. Die Bildung „lebender” Polymerer bei genugend niedriger Temperatur, die von der Dielektrizitatskonstante des Losungsmittels abhangt, wird angenommen.

The intensity of respiration and of photosynthesis were investigated simultaneously in sugar-beet leaves not detached from the plant. Several hours before the experiment the leaves had assimilated radioactive14CO2 whereafter they were placed into a normal leaf chamber for continuous gasometric estimation of the intensity of photosynthesis, according to the changes in the concentration of carbon dioxide in the passing air. At the same time, the specific activity of C02 was measured in the air that had passed through the assimilation chamber. From the values of the specific activity of CO2 produced by the leaf in the dark the intensity of respiration in mg. CO2 can be calculated.