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At least 55 records · Page 3Linked to original sources
PubMed1956

Oxygen protection of bacteriophage T1 against ionizing radiations.

Bacteriophage T1 was suspended in distilled water and in phosphate buffer, saturated with oxygen, nitrogen, hydrogen, and carbon monoxide, and irradiated with gamma rays and x-rays. Under the same conditions phage was exposed to hydrogen peroxide. Oxygen acted as a protective agent against both irradiation and hydrogen peroxide inactivation. As a protective agent against irradiation, oxygen was more efficient in distilled water than in buffer. The phage was much more sensitive to irradiation in the presence of hydrogen or nitrogen than in the presence of oxygen. Survivals of phage irradiated in suspensions saturated with hydrogen and with nitrogen did not differ significantly. From this it was concluded that oxygen did not protect T1 by removing atomic hydrogen from the irradiated medium, since the hydrogen-saturated medium increased the yield of atomic hydrogen but did not increase the yield of inactivated phage. It was presumed, therefore, that phage is sensitive to OH radicals and this was confirmed by irradiating phage with UV in the presence of hydrogen peroxide and comparing this survival with the survivals obtained from hydrogen peroxide alone and from UV alone. The combined effect of hydrogen peroxide and UV acting simultaneously was greater than the effect attributable to hydrogen peroxide and UV acting separately. Evidence for sensitivity to HO(2) radicals was considered, and the effect was attributed chiefly to an oxidizing action since phage sensitivity is greater at higher hydrogen ion concentrations, which favor oxidation by HO(2) radicals. Since the OH radical is a more efficient oxidizing agent than O(-), the former being favored in an acid medium, the latter in an alkaline medium, and since the phage is more sensitive in the first situation than in the second, the present tests proved the importance of oxidation as the mechanism of inactivation. Since some inactivation was encountered when phage was exposed to reducing agents, independently of irradiation, it was concluded that phage is somewhat sensitive to reducing agents, but the inactivation attributable to ionizing radiations is due chiefly to oxidation, against which these reducing agents are very efficient protectors. Under no circumstances did hydrogen peroxide protect T1, whether produced by irradiation in the medium or added beforehand to the medium to be irradiated. The first point was investigated by irradiating T1 in the presence of hydrogen and oxygen combined; this produced a higher yield of hydrogen peroxide but a lower survival of T1. In all these tests phage survival under irradiation was directly correlated with oxygen content of the medium rather than with production of hydrogen peroxide. It is proposed that the protective effect of oxygen is due to a reaction between the phage and oxygen, and this complex confers stability upon the phage.

Bacteriophages↗
PubMed1958

Transmission in squid giant synapses: the importance of oxygen supply and the effects of drugs.

Synaptic transmission was studied in giant synapses of the stellate ganglion of the squid. When bathed in air-saturated sea water, the synapses deteriorate in 10 to 20 min.; if the sea water is saturated with 100 per cent oxygen, they function steadily for up to 12 hours. Optimal results probably require a medium with lower magnesium and higher calcium than the sea water used. Of eighteen compounds known to affect other synapses (Table I), none had stimulatory effects when applied to the preparation, but ten produced synaptic depression in concentrations of 10(-3) gm. per ml. or higher. The only exception was procaine, which blocked at 6 x 10(-5) gm. per ml. Intracellular recording with microelectrodes near the synapse showed that the block was associated with a slower rise of the excitatory post-synaptic potential, without a change in the depolarization required to initiate the spike. Procaine was exceptional in also increasing the depolarization at which the spike occurred.

Animals↗
PubMed1958

The production of hydrogen peroxide by high oxygen pressures.

Hydrogen peroxide is formed in solutions of glutathione exposed to oxygen. This hydrogen peroxide or its precursors will decrease the viscosity of polymers like desoxyribonucleic acid and sodium alginate. Further knowledge of the mechanism of these chemical effects of oxygen might further the understanding of the biological effects of oxygen. This study deals with the rate of solution of oxygen and with the decomposition of hydrogen peroxide in chemical systems exposed to high oxygen pressures. At 6 atmospheres, the absorption coefficient for oxygen into water was about 1 cm./hour and at 143 atmospheres, it was about 2 cm./hour; the difference probably being due to the modus operandi. The addition of cobalt (II), manganese (II), nickel (II), or zinc ions in glutathione (GSH) solutions exposed to high oxygen pressure decreased the net formation of hydrogen peroxide and also the reduced glutathione remaining in the solution. Studies on hydrogen peroxide decomposition indicated that these ions act probably by accelerating the hydrogen perioxide oxidation of glutathione. The chelating agent, ethylenediaminetetraacetic acid disodium salt, inhibited the oxidation of GSH exposed to high oxygen pressure for 14 hours. However, indication that oxidation still occurred, though at a much slower rate, was found in experiments lasting 10 weeks. Thiourea decomposed hydrogen peroxide very rapidly. When GSH solutions were exposed to high oxygen pressure, there was oxidation of the GSH, which became relatively smaller with increasing concentrations of GSH.

Glutathione↗