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The inactivation of homozygous yeast strains of different ploidy by some dyes in the presence and in the absence of visible light was investigated and the results were compared with the reactions of thiopyronine. The influence of some of these dyes on nucleic acids was also examined.Only those dyes which gave precipitates with nucleic acids in aqueous solution activate yeast cells in the absence and — even in smaller concentrations — in the presence of visible light.

Energy metabolism and repair of U .V. damage in Saccharomyces 1. The effect of glucose on recovery of UN . -sensitive mutants B.Liquid-holding recovery in Saccharomyces was found to depend on glucose concentration during pre-irradiation treatment or during the liquid-holding period in the wild type and in mutant strains rslr',, rS2rs2i rss_ 2rs3_2. The maximum glucose enhancement effect on survival was about 15 per cent in wild-type, 40 per cent in rs,rs,, 20 per cent in rs2rs2 and 3 per cent in r s3_2r S3-2 mutants at a buffer concentration of 4 x 10 -10 g glucose per cell . Concentrations greater than 10 -' g glucose per cell cause a decreasing effect on liquid-holding recovery . The results are discussed in view of different energy pathways and the lack of repair capacities in the strains used .2G Int J Radiat Biol Downloaded from informahealthcare.com by McMaster University on 12/02/14For personal use only.

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The oxidation of ferrous to ferric iron is used as a measure of the effect of ionizing radiation in Fricke dosimeter solution in the presence of glycerine at various concentrations. At low glycerine concentrations the sensitivity of the system to X-rays was found to be increased by the presence of the alcohol while at higher concentrations a radiation-protection effect was observed. The increased sensitivity rose to a maximum at glycerine concentrations of 0.01 to 0.1 Mol, the size of the maximum depending on the duration of the radiation. The peak represents a sensitivity of about twice the normal ion conversion. The falling off at low concentrations is explained on the basis of a model where the presence of alcohol leads directly to increased ferric ion yield, that at high concentrations as being due to increased viscosity of the system. Other alcohols showed similar results.