Effect of sodium azide on radiation damage and photoreactivation

Metabolic activation of the mutagen azide in biological systems

Inorganic azide (N3-) mutagenicity is mediated through a metabolically synthesized organic azide, L-azidoalanine (N3-CH2-CH(-NH2)-COOH). L-Azidoalanine appears to be formed by the action of O-acetylserine (thiol)-Lyase (EC 4.2.99.8) using O-acetylserine and azide as substrates. In both plants and bacteria tested, azide substitutes for the natural substrate sulfide (S2-) in this reaction. Azide (L-azidoalanine) mutagenesis is highly attenuated by a deficiency in the excision of UV-like DNA damage (uvr-). Thus a premutation lesion recognizable by the bacterial excision-repair enzymes must be formed. Mutagenesis appears to proceed from this by 'direct mispairing' pathway. Azide (L-azidoalanine) mutagenicity is highly specific and involves a stereoselective process, but the molecular nature of the specificity has not been determined.

Effects of pH on the mutagenicity of sodium azide in Neurospora crassa and Salmonella typhimurium

Sodium azide at various pH values did not cause a significant increase in the frequency of forward mutation above the control frequency at the adenine-3 (ad-3) region in resting conidia and in conidia from growing cultures of heterokaryons 12 and 59 of Neurospora crassa. Conidia from ad-3 mutants were plated with sodium azide at various pH values, and no obvious increase in reverse mutation above the controls was observed. Data are presented showing that sodium azide at pH 3 is inactivating conidia by interacting with the cytoplasma rather than the nucleus, and this may be the primary reasons that no mutation at the ad-3 region was detected. The dependence of sodium azide mutagenicity on pH was investigated in histidine-requiring mutants of Salmonella typhimurium using a suspension test. There were no significant differences in the reversion frequencies among the pH values (3-8) tested. Thus, no pH dependence is associated with sodium azide mutagenicity, nor are growth and/or DNA replication required for mutagenicity by sodium azide, in S. typhimurium.

AMINO ACIDS AS PROTECTIVE COMPOUNDS IN ULTRAVIOLET-IRRADIATED HANSENULA WINGEI

Hunt, D. E. (Charles V. Chapin Hospital, Providence, R.I.). Amino acids as protective compounds in ultraviolet-irradiated Hansenula wingei. J. Bacteriol. 88:893-895. 1964.-"Prefeeding" Hansenula wingei with small concentrations of either tryptophan, cystine, tyrosine, phenylalanine, leucine, cysteine, threonine, isoleucine, ethionine, norvaline, or histidine protected this yeast against inactivating ultraviolet treatment. "Prefeeding" with methionine, proline, or alanine conferred little if any protection, and valine or serine caused this organism to be more sensitive to ultraviolet inactivation. A direct relation exists between the concentration of the protective amino acids and the number of surviving cells. The heterocyclic and aromatic amino acids are generally more protective than the corresponding aliphatic compounds. The diversity of the compounds as well as quantitative differences in the protection afforded by them suggest that they have different modes of action.

SOME EFFECTS OF POSTIRRADIATION TREATMENT WITH METABOLIC INHIBITORS AND NUTRIENTS UPON ULTRAVIOLET IRRADIATED SPORES OF STREPTOMYCES T12

The effects of postradiation treatment with metabolic inhibitors (arsenate, azide, and dinitrophenol) and various cell nutrients (N-sources and sugars) upon ultraviolet irradiated spores of Streptomyces T12 have been studied. Changes in the frequency of induced variants which were not accompanied by effects upon survival, and increases of survival which were not associated with a change in variant frequency were observed. The results obtained indicate that the biological effects of ultraviolet radiation can be modified by the postradiation metabolism of the cell.

RELATIONSHIPS BETWEEN POSTRADIATION TREATMENTS WITH IODOACETATE AND LIGHT

When ultraviolet irradiated spores of Streptomyces T12 were treated with iodoacetate for periods of up to six and a half hours and then photoreactivated, the proportion of survivors was greater than that for control spores similarly treated in distilled water. The frequencies of variant colonies from spores treated with iodoacetate and photoreactivated did not differ significantly from those obtained when spores were similarly treated in distilled water. The principal effect of iodoacetate treatment was inhibition of the loss of photoreversibility, as measured by the effect upon proportion of survivors.