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  • Author: Werner Stein x
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Former results of radiation inactivation in homozygous and isogenic yeast strains of different ploidy are compared with equations of target theory. For this purpose it is recessive to consider genetical and plasma lethal processes separately. The induction of recessiv lethal mutations proved to be in fair agreement with an expression developed by POLLARD and coworkers. The rising as well as the declining part of the RBE curve are explained by this equation. The calculated cross section of the target seems to be very similar to that of the cell nucleus.

The plasma lethal effects are probably also in agreement with this theory.

On the other hand there are difficulties in explaining the RBE curve for dominant lethal mutations in the same way.

Inactivation of E. coli strain B by H2O2 treated broth has been studied in relation to peroxide concentration and time of contact. The rate of survivals was found to depend on the product of these two values. Below a certain limit of this product there occurred a reactivation by incubation at higher temperatures that showed a DRF value of (3-4) : 1; after UV irradiation this value is (10-20) : 1. There was also found a reactivation of peroxide inactivated cells by irradiation with wave lengths > 312mμ. The average DRF value obtained was 1,3 : 1 whereas after UV irradiation this value was about 4 : 1. Although the greater part of peroxide inactivation is connected with irreversible processes probably in the cytoplasm the conclusion is drawn that the reversible part of peroxide inactivation proves the idea that UV inactivation is related to a secondary production of poisons similar to organic peroxides.

The following experimental results were obtained: Inactivation of Escherichia coli, strain B, by wave-lengths from 254 mμ to 313 mμ is strongly heat-reactivable with a dose reduction ratio of about 12 : 1 to 7 : 1, respectively. But there is little or no heat-reactivation after inactivation by wave-lengths of 334 mμ, 366 mμ or about 560 mμ. Resistance of strain B/r, closely correlated with the heat-reactivability of strain B, disappears at wave-lengths ≧ 334 μ too. The inactivation efficiency of quanta absorbed by the whole bacterium decreases between 254 mμ and 366 mμ by a factor of nearly 103; if only absorption by DNA of the cell is considered, the factor ist also 103. Hence, it is concluded that a rapid change in the mechanism of inactivation takes place just between 313 mμ and 334 mμ, which is probably caused by the critical limit of a definite quantum absorption. As an interpretation for inactivation by long UV and visible light denaturation of proteins and lethal mutations are discussed.

The dose-effect curves for radiation- (especially ultraviolet-) induced mutations sometimes show saturation effects or maxima at the higher dose range. These phenomena either could be typical for the radiation induced mutation process and consequently contributing to its analysis, or could be caused by mere secondary effects. The following possible interpretations are given and are discussed by aid of mathematical methods: (1) Higher probability to be inactivated for the mutating individuals than for normal ones, (2) non-manifestation of the mutated phenotype as the result of interference with other mutations, (3) radiation induced formation and (at higher doses) destruction of mutagenic substances within the cell, (4) inhomogenity of the population with respect to radiation sensitivity and/or mutability. — Some experimental data described in the literature are proved in account of their compatibility with such interpretations. In certain cases a plausible conformity could be shown.

In Ergänzung zu früheren Arbeiten werden die Ergebnisse von verschiedenartigen Versuchen zur Reaktivierung UV- und peroxyd-inaktivierter Coli-Stämme (B, B/r und 15 [h-]) mitgeteilt. Es wurde Wärme- und Kälte-Reaktivierung auch außerhalb des physiologischen Bereichs (bei + 48° C und + 6° C) festgestellt. Im Zusammenhang mit „Schwemmversuchen" “ erwies sich, daß die Temperatur-Reaktivierung spätestens mit der ersten Zellteilung abgeschlossen ist. Die Einwirkung höherer Temperaturen vor der Bestrahlung ergab je nach den Bedingungen unterschiedliche Effekte. Relative Empfindlichkeit und Temperatur-Reaktivierbarkeit der drei Stämme stimmten für Peroxyd- und indirekte UV-Inaktivierung weitgehend überein. Diese Ergebnisse für beide Inaktivierungsarten waren wiederum sehr ähnlich denen für direkte UV-Inaktivierung, nur war die Temperatur-Reaktivierbarkeit höher als bei dieser. Versuche mit kombinierter Photo- und Temperatur-Reaktivierung zeigten eine weitgehend unabhängige Überlagerung beider Reaktivierungs-Effekte. Während die Dosis-Reduktion für die Temperatur-Reaktivierung von Stamm zu Stamm stark variiert, ist sie für die PhotoReaktivierung nur wenig unterschiedlich.

Es wird ein Überblick über besonders kennzeichnende Ergebnisse bzgl. UV-Inaktivierung von E. coli und veschiedener Reaktivierungs-Effekte gegeben. Die Deutungsmöglichkeiten werden an Hand des Schemas „Absorption — Zwischenprozesse — Wirkung“ kritisch diskutiert. Schließlich wird im Sinne einer Arbeitshypothese eine Modellvorstellung entwickelt, deren Konsequenzen besprochen werden. Danach sind direkte Inaktivierungs-Effekte weniger häufig als zeitlich indirekte; letztere werden erst über Sekundärprozesse realisiert, in die Photo- und Wärme-Reaktivierung an bestimmten, im Modell angegebenen Stellen eingreifen. Der UV-Resistenzunterschied zwischen B- und B/r-Stamm ist danach vorzugsweise in wärmereaktivierbaren, indirekten, nichtgenetischen Letal-Effekten zu suchen.

Abstract

Leading motif for the article is the lack of serious historical research regarding the economic integration processes in Europe since the end of World War II. It starts with a closer look at the economic theory to examine its practicability to explain integration. The article continues with an investigation of the various phases of economic integration in the East and in the West after World War II. In addition to that, continuative questions are raised. The paper’s major hypothesis is, that integration in East and West was led by political issues rather than by questions of economic efficiency. In light of this, the limited economic effects are actually not surprising.

Experimental data, published in parts I to III of this paper are discussed in respect to specific biological effects responsible for the inactivation of yeast cells by different radiations and organic peroxides. It was differentiated between four biological processes using the experimental results and certain theoretical considerations fitted to a special series of homozygous yeast strains of different ploidy. These four processes are: cytoplasmatic inactivation dependent and independend on ploidy, recessive and dominant lethal mutations. The influence of the “aa-effect“ (resistance to ionizing radiations) observed in diploids heterozygous only for the mating type alleles (aa) and supposed in all strains able to sporulate is discussed and its possible extend estimated.