Joe Atsuta

Necessity of Glycolysis for Recovery from Ultraviolet Killing of Saccharomyces cerevisiae

respiratory rate of diploid yeast: Survival was consistently high in cells grown in anaerobic complete medium where only glycolysis was operating, while it was low in cells grown in aerobic glycerin medium where only oxidative phosphorylation was operating; these observations are consistent with the observed shift from the high resistance in logarithmic phase to the lesser resistance in stationary phase in cells grown in aerobic complete medium. Immediate recovery, which was determined by the ratio between split-dose survival and no recovery survival, occurred only in cells having a low respiratory rate and not in cells having a high respiratory rate. Severe suppression of aerobic ATP synthesis during the first hour after irradiation was found only in cells having a high respiratory rate. Otherwise, delayed recovery, which was determined by immediate plating on glycerin medium, was not related to the respiratory rate. These results indicate a low resistance to uv of oxidative phosphorylation in mitochondria existing at the time of irradiation and a high resistance to uv of both glycolysis and oxidative phosphorylation in new mitochondria produced after irradiation. Survival therefore may be dependent on whether irradiated cells can recover from sublethal damage by utilizing ATP produced by glycolysis immediately after irradiation.

Effects of X Irradiation on Respiratory Control and P/O Ratio in Isolated Rat Liver Mitochondria Having Different Respiratory Control Ratios

The respiratory control and P/O ratios of isolated rat liver mitochondria held aerobically in buffered 0.3 M mannitol-0.2 mM EDTA in an ice bath decreased exponentially immediately after X-irradiation at 20,000 R, in close correlation with the decrease of the preirradiation respiratory control. Of the two indicators of mitochondrial intactness, the respiratory control was the more sensitive to irradiation. This radiation effect appeared to be similar to uncoupling. The losses of respiratory control and P/O ratio in the irradiated mitochondria were amplified by transfer to ice-cold buffered 0.15 M mannitol without EDTA; the degree of this amplification reached a maximum for values of the preirradiation respiratory control ratio in the neighborhood of 4.0. The nature and direct cause of the radiation damage in mitochondria are discussed.

Modification of the Effect of Ultra-violet Irradiation by a Nutritive Condition on the Induced Formation of Catechol Oxygenase in Pseudomonas Effusa

Summary(1) The effect of ultra-violet radiation on the induced synthesis of catechol oxygenase was very different according to nutritive conditions of Pseudomonas effusa.(2) Significant damage to catechol-oxygenase synthesis depending on translation was observed under the enriched condition, whereas it was not affected under the deficient condition, by a dose sufficient to block induction.(3) From comparison of inhibiting modes, it is concluded that u.v.-irradiation under the enriched condition has an inhibitory effect on both transcription and translation. Under the deficient condition, a preferential damage on transcription is observed, whereas translation is not affected.

Sensitivity to ultraviolet light of RNA synthesis under different culture conditions in Pseudomonas effusa.

Comparative studies were made on the sensitivity of the synthesis of individual ribonucleic acids (RNA) components to ultraviolet light (UV) under conditions that (A) suppressed ribosomal RNA (rRNA) synthesis and permitted preferential synthesis of messenger RNA (mRNA); (B) permitted balanced synthesis of individual RNA components; and (C) suppressed mRNA synthesis and permitted preferential synthesis of rRNA. Under condition A, mRNA synthesis was found to be much more UV-sensitive in the presence than in the absence of inducer. Under condition B, no preferential inhibition of the synthesis was observed for any one of the mRNA peaks. Synthesis of rRNA was more readily found to be UV-sensitive with the increasing molecular weight of RNA under condition C than under condition B.

Modification of the effect of ultra-violet irradiation by a nutritive condition on RNA-synthesis during the induction of catechol oxygenase in Pseudomonas effusa

Summary(1) The effect of ultra-violet irradiation on the synthesis of RNA was very different according to nutritive conditions of Pseudomonas effusa.(2) There was significant damage to the synthesis of mRNA, dependent on the inducer, under both the deficient and the enriched conditions by u.v.-irradiation with a dose sufficient to block the induced synthesis of catechol oxygenase.(3) u.v.-irradiation under the enriched condition had an inhibitory effect on the synthesis of rRNA.