摘要:

Abstract.A study of the relative sensitivity of bromouracil and thymine to photochemical alteration (2537Å) when incorporated into the DNA of bacterial cells has led to the conclusion that bromouracil is about twice as reactive as thymine. This offers a chemical basis for the sensitization of bacteria to ultraviolet light by incorporated bromouracil.Bromouracil forms at least five photoproductsin vivo. The relative proportions of these several photoproducts is significantly different inE. coliB/r andEnterococcusStei. Uracil is the chief photoproduct of bromouracil inEnterococcusStei but inE. coliB/r the major photo‐product (which is a minor product inEnrerococcusStei) is as yet unidentified.Preliminary data on the five to nine decomposition products of the dimer of bromouracil and the mixed dimer of uracil and bromouracil (produced in irradiated frozen solution) have suggested a tentative explanation for the differences in products in the two organisms. The results forEnterococcusStei appear consistent with the asumption that the major photo‐product of bromouracil is the dimer and this then decomposes to yield mainly uracil (as it doesin vitro). E. coliB/r takes up less bromouracil and the photoproducts formed resemble more closely those found for thein vitrodecomposition of the bromouracil‐uracil dimer. These results suggest that the primary photoproduct of bromouracil inE. coliB/r may be either a mixed dirner (intrastrand) with cytosine (with the subsequent deamination of the cytosine) or an interstrand crosslink with either bromouracil or cytosine.Thymine forms at least four photoproducts other than the dimer. Two of these photoproducts are significantly elevated in that portion of the bacterial DNA that is rendered non‐extractable by detergent after ultraviolet irradiation (remains associated with protein) and are also found in irradiated poly‐dAT.From the rate of formation of thymine dimers in irradiated (2537Å)E. coliB/r it can be calculated that approximately 1 erg/mm2produces one th

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07845.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Abstract.Microscopic observations show that growth delay and division delay occur on nutrient agar afterEscherichia coliB has been irradiated at 3341 Å. These effects also occur in nutrient broth.A near u.v. action spectrum for growth delay in nutrient broth has been obtained. It shows a single peak at 3380 Å and is indistinguishable from the action spectrum for photo‐protection from far u.v. (2537 Å) killing in the same organism. Furthermore, photoprotected cells show a much greater growth delay than cells that have not been photoprotected. These, as well as kinetic data, suggest that the essential action of a photoprotection treatment consists in the induction of a growth‐division delay. This delay would presumably permit more time for intracellular recovery systems to operate on the far u. v. damage to nucleic acids.Liquid holding recovery (effected by holding cells in phosphate buffer after far u. v. irradiation) shows complete overlap with photoprotection. It is concluded that photoprotection and liquid holding recovery operate on the same far u. v. damage. As with photoprotection, it is probable that the essential action of a liquid holding treatment is the induction of a growth‐division delay.No photoprotection is observed of intracellular T2 bacteriophage or ofE. coliBs

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07846.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Abstract.The present paper gives an account of the phenomenological theory underlying the three dimensional distribution of excitons in solids. General expressions for the steady state distribution are derived taking into account the bulk and surface and annihilation generation of excitons, the influence of sample geometry and fluorescent reabsorption effects. The wave form of the optical excitation has also been included for purposes of generality. Approximations to the general results are provided for certain special cases which may apply to organic solids.

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07847.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Abstract.The plaque forming ability of theE. coliphage fr, containing single stranded RNA, is highly UV‐resistant. One lethal hit corresponds to approximately 1'2 × 105erg cm‐2. photoreactivation of fr due to illumination of infected bacteria has not been found after UV‐inactivation of either extracellular or intracellular phage. This shows that the already known PR‐enzyme ofE. coliK12 is probably specific only for some of the UV‐lesions in DNA but not in RNA. Furthermore, it may indicate that the photoreactivation of some RNA‐containing plant viruse(1,2)is due to a PR‐enzyme which is not present in K12.UV‐inactivated fr is also not host‐cell‐reactivable. The plaque forming ability of fr infected bacteria decreases rapidly with increasing doses of PR‐light wherea: the colony forming ability of uninfected host cells is very

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07848.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Abstract.The possibility of increasing the cell resistance to short‐wave u. v. rays has been investigated with some chemicals. Ciliated epithelium cells of gills of pearly musselUnio crassusPhillipsson have been shown to become more resistant after treatment with 0.25–0.50 per cent solutions of calcium chloride during 24 hr or by 0.001– 0.001 per cent solutions of 2‐benzyl‐benzimidazole during 3–7 days or by 0.0001 per cent solution of 5–6‐di‐methyl‐benzimidazole during 7 days. When irradiated with u. v. light (λ=2537 Å) these cells survive for a longer time than irr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07849.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Abstract.Data are presented showing how fluorescent filters can be used to increase the efficiency of illumination processes, especially when using light sources with high colour temperature (as for instance flash lamps in flash photolysis or in LASER pumping).

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07850.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Abstract.A kinetic model is proposed to account for the time/intensity response curves for the photo‐inhibition of stem elongation inPisumandTropaeolum. Two separate mechanism are involved; the first inhibiting effect reached a constant value in a time small compared with the time scale of the experiments, and the second was an exponential function of the daily duration of irradiatio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07851.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

Abstract.Angiotensin is readily inactivated by ultraviolet light presumably due to the photosensitivity of its tyrosyl and phenylalanyl residues. Alkalinity promotes and acidity delays the biological decomposition. Under conditions of oxygen exclusion (i.e. under N2or H2) the rate of decomposition is further depressed and when irradiation is carried out under hydrogen a biologically active product is formed. This altered angiotensin, judging from its chromatographic migration and dialysis rate, represents a polymerized form of angiotensin. Under identical irradiation conditions, angiotensin was coupled with C14labelled pheny‐lalanine which indicates that this residue might be the photoreactive species. The production of altered forms of angiotensin by ultraviolet irradiation was discussed with respect to possible utility in anti‐metabolite, antigen or tracer w

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07852.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07853.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1964.tb07854.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY