Radiation-induced changes in the third instar larvae of Musca domestica were investigated. Pupariation delay was evident in the irradiated larvae. Both 5 and 10 kR exerted similar pupariation delays.
At biochemical level, glycogen seems to show an enhancement in the irradiated larvae as compared to control. Free sugars register initial rise followed by decline in the irradiated larvae. Total ninhydrin positive compounds showed a similar trend as free sugars. The irradiated larvae exhibited a delayed increase in protein content as compared to control. There was no significant change in ribosidic compounds due to irradiation. These results are discussed in the light of the likely targets of radiation at the cellular level.

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Aqueous thymine solutions were irradiated with Co-60 gamma source in presence of sufficient N₂O(125 mM) in order to study the fate of the hydroxy-thyminyl radicals i. e. thymine and OH radical adducts. These adducts appeared to end up with production of about nine different products including three dimeric ones. These substances were separated on paper chromatogram using n-butanol :water= 86: 14 v/v and confirmed by mass spectrometric analysis and dehydration kinetic studies. Their yields were determined by tracer method using scintillation counting. Good material balance was achieved.

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Larvae of different ages from 40 hr to 72 hr were exposed to γ-rays ranging between 500R and 10000R ; all ages of the larvae showed dose-dependence pupariation delay up to 4000R. The shape of the puparia were not normal in the larvae irradiated with higher doses. Sparing effect of dose fractionation (SDF) was demonstrated for the pupariation delay. Sparing effect was quite marked at low dose-rate (15R/second) than at high dose-rate (80R/second) and maximum SDF was found with 2 hr interfraction interval as compared to 4.5 and 6.5 hr. The magnitude of SDF was comparatively less at 15°C than at 35°C indicating the occurrence of repair. Furthermore, the metabolic requirement of repair processes was evidenced by the abolition of SDF by inhibitors of energy metabolism, DNA binding agents and protein synthesis inhibitors.

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N-formamido-(DNA) is one of the main lesions formed on the thymidylic fragments of DNA when DNA, in vitro or in vivo conditions, is exposed to ionising radiations. The N-formamido group partly replaces the thymine base in DNA sequence.
This article proposes an indirect dosing technique for this damage. The method is based on the release of ¹⁴CO₂ from the C-2 of the thymine ring. When the pyrimidine ring of the thymidine moiety is broken, N-formamido deoxyribose derivative, carbon dioxide and pyruvamide are formed all in the same reaction. During this investigation the phenomena of protection due to the constituent parts of the cell and to the secondary and tertiary structures of DNA are also evidenced.

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Distribution and retention of tritium in various tissue of a rat after administration of tritiated water (HTO) was investigated during about 100 days. Tritium incorporated into the body was rapidly and uniformly distribution in the whole body and excreted immediately with a biological half-life of 3.5 days for almost all the tissues. However, excretion of tritium incorporated into the tissue constituents was relatively slow and the retention curves were considerably different from tissue to tissue. At the end of this experiment, the highest concentration of total tritium was observed in the fat tissue, followed by brain and muscle. These results suggested that the intake of tritium from HTO into organic compounds and the excretion of tissue-bound tritium would be related to metabolic activity of the tissue. This prediction was reinforced by the experiment on age dependence.
The radiation dose to each tissue after the administration of 6.0 μCi/g body weight of HTO ranged from 2.0 to 9.5 rem, which was the highest in blood and the lowest in fat tissue. Contribution from tissue-bound tritium was within 10% of the dose from total tritium for each tissue, except for fat tissue which was 64%.

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It has been reported previously that the UV irradiation of mushroom tyrosinase resulted in a logarithmic loss of biological activity due to the conformational changes in the enzyme molecule. The purpose of the present study was to investigate the factors influencing the radiosensitivity of enzymatic activity. A similar rate of the catalytic activity loss at different pH supported the attribution to the conformational change -of the enzyme molecule but not to the active site damage. The presence of potassium chloride and the absence of oxygen resulted in only a little protection against enzyme photo inactivation. Activity survival curve as a function of radiation dose at a higher enzyme concentration showed to have a shoulder which indicate the mutual protection of the enzyme molecules. Copper (II) protected the loss in catalytic activity of enzyme on irradiation. This was explained in terms of scavenging of the hydrated electron by copper (II). Therefore, it was concluded that photoinactivation of this enzyme was mainly due to conformational changes caused by the damage of constitutional aromatic amino acid residues but also partially due to inactivation of copper of enzyme with hydrated electron.

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It has been reported that the chloroform-paraffin-dye system have excellent sensitivity for radiation as a solid chemical dosimeter or a phantom. However, the chemical changes in the irradiated system are not examined in detail. In the present study, the effect of paraffin on changes in the above system of a liquid state irradiated by ⁶⁰Co γ-rays was examined by using various normal paraffin, and the other variable factors on the changes were done.
When the chloroform solution and the solution containing 25 per cent of paraffin by volume with 5.0×15^-5 mol/liter of Methyl Yellow as a dye were irradiated by 2000 R, G values for the formation of hydrogen chloride in the both solutions were 8.4 and 10.8, respectively, and were little affected by the kind of those, from C₀ (hexane) to C₃₆ (hexatria-contane). These results suggest that chlorine radical formed by radiolysis of chloroform may react with hydrogen atom from paraffin, thereby increasing the amount of hydrogen chloride. Presence of oxygen increased G value of the chloroform solution from 7.6 to 8.4, but did little that of the solution containing paraffin.

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Rate constants for the reactions of Cl₂^- with several aliphatic amino acids were determined in neutral aqueous solutions of potassium chloride (0.1 M) using a conventional flash photolysis apparatus. The reactivity pattern of Cl₂^- radical toward aliphatic amino acids was found to be similar to that of OH radical, although the reaction rate of the former is about two orders of magnitude smaller than the latter. The result suggests that the reaction of Cl₂^- with aliphatic compounds is hydrogen atom abstraction. It was found that the reactivity for the branched amino acids is relatively low and the difference in reactivity toward the branched amino acids between Cl₂^- and OH radicals was discussed in terms of steric effect.

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Inhibitory effects of raddiation on the regeneration of fin of the fish, Oryzias latipes, irradiated before fin amputation was examined. Both whole body and local irradiation of the fin region alone suppressed the elongation of fin and prevent cell differentiation into fin rays dependent on the given dose. The earlier processes of the regeneration, wound healing and blastema formation, were relatively resistant to radiation.
Reduction in the dose-rate resulted in a sparing effect on the radiation damage. In spite of the serious inhibition of the fin regeneration resulted from acute (250 R/min) irradiation of 4 kR, irradiation performed at exposure-rate reduced to 25 R/min or less did not prevent fin regeneration at least in the examination of the fin elongation.

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