摘要:

Abstract—Ultra‐violet irradiation of oxygen‐free solutions of 9‐methyI anthracene leads to the formation of both stable dimers and metastable excimers. The fluorescence spectra of concentrated solutions show an excimer emission band. This behaviour is attributed to the partial steric hindrance of dimer formation by themeso‐sub stituent, and it is proposed that the stable dimers and excimers correspond to anti‐parallel and parallel configurations of the two monomers respectively. A consideration of the monomer fluorescence data for anthracene and itsmeso‐substituted derivatives suggests that steric hindrance similarly reduces the interactions with solvent molecules which lead to inter

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08898.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—The decrease in absorbance at 2600 Å of poly‐U following u.v. irradiation is analyzed quantitatively in terms of uracil‐dimer formation and photohydration of uracil residues. At all wave lengths tested between 2300 and 2800 Å both dirner formation and hydration occur as well as dimer breakage. The cross section for uracil dirner breakage is large at 2300 and decreases to a relatively small value at 2800 Å. Consequently, at the shorter wave lengths the steady state for dimer formation and breakage is reached at lower doses than for the longer wave lengths. Absorbance decreases caused by longer wave lengths can be partially restored by irradiation with 2380 Å. At high doses, for all wave lengths, the main photoproducts are hydrated uracil residues. The maximum number of dimers that may be formed increases with wavelength. The absorbance loss caused by photohydration may be reversed by acidification and heat. For 2650 Å irradiation, 95 per cent of the absorbance is restored by a combination of the 2380 Å and thermal treatment. The values for the photochemical reactions of poly‐U are fairly close to those for poly‐T

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08899.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—The photoreactivation rate of U.V. irradiated phages is decreased in u.v. irradiated bacteria. In contrast, the normal photoreactivation rate is observed if the irradiated bacteria are photoreactivated before phage infection. The decrease of the photoreactivation ratc is understood as a competing effect of the u.v. lesions in the bacterial nucleic acids for the photoreactivation enzyme. This competitive inhibition can be diminished not only by photoreactivation of the bacteria before phage infection but also by hostcell reactivation of the u.v. lesions in the bacterium. The results provide strong evidence that hostcell reactivation and photoreactivation revert the same u.v. photoproducts in bacterial nucleic acids. The experiments show that the hostcell reactivation enzyme is not induced by phage infection or by irradiation, but is normally present in the bacterial cel

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08900.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—The redox dependence of the light‐induced electron paramagnetic resonance signal at g=2 inR. rubrum, R. spheroidesandChromatiumchromatophore particles and quantasonie particles from spinach chloroplasts has been determined qualitatively over the range —0.3 to +0.6 V and quantatively over the range +0.3 to ±0.6 V. A light‐induced EPR signal has been titrated and demonstrated to have a midpoint potential of +0.44 v at pH 7 and 20°C. Concentration, ionic strength and pH dependence for this transition inR. rubrumchromatophores is reported. In addition to the dark signal which replaces the light signal, in chromatophore material another dark signal, occurring in the seine location as the light signal, has been demonstrated to occur at high potential.Selective chemical oxidation with K2lrCl6of chromatophore particles from the three bacteria resulted in the removal of some 95 per cent of the absorbance in the near infrared and left the photoactive pigments.Two light‐induced EPR signals were found in quantasome particles by their dependence upon the redox level. Of particular interest is a signal observed at quite high potential (e.g. + 0.60 V). It was demonstrated that oxygen evolution by these quantasonie particles in the presence of K3Fe(cN)0occurred at the same rate at +0.55 V as

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08901.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—Thymine and uracil dimerized by ultraviolet irradiation (principally at 253 7 mμ) on filter paper and on quartz fiber sheet show a fairly good yield. These irradiation products were identical with the photodimers prepared from frozen aqueous solution. Thymine and uracil dimer in an aqueous solution reverted to the original pyrimidines by the ultraviolet irradiation with quantum yields of 0.65 and 0.50 respectively. Uracil dimer was rather labile towards hot alkaline solution. In neutral and acidic media, both dimers were quite stable. Photodimers of cytosine and isocytosine were not obtain

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08902.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—In the non‐photoreaclivable bacterial strainE. coliB/phr‐/MC2 the photoreversion of four groups of u.v.‐induced mutations were investigated. They lead to resistance to Chloramphenicol (2 mg/l; “C”), Penicillin (13 or 16 mg/l; “P13” and “P16”) or Streptomycin (3 mg/l; “S”). The u.v.‐dose curve is concave for the C‐mutations (two to three hits), about linear for P13 and S, and they reach peaks and decrease at high u.v.‐doses. Though no photoreactivation of killing (PR) is present there is photoreversion of all four types of mutations (PRM). At u.v.‐doses below the peaks in average about 43 per cent mutations are photoreversible. At high u.v.‐doses the curves with light‐post treatment (L) cross the darkcurves (D). In the photoreactivable strain B/r (by the spontaneous mutation MC2 to Mitomycin‐resistance strain B/phr‐was made about as u.v.‐resistant as B/r is) the photoreversion of the mutation groups C, P13 and P16 (S was not investigated here) was much higher, in average about 77 per cent at low doses. It is assumed that the difference in PRM of about 34 per cent between both strains is due to a PRM‐mechanism present in B/r but not in B/phr‐/MC2; this mechanism may be the photoreactivating enzyme that opens thymine‐dimers. The PRM in B/phr‐/MC2 must then be due to a second mechanism which is probably not the dimer opening enzyme. It may be the same mechanism as in the case of mutations of phage kappa which are induced by u.v. and reversed partially by light, both extra cellularly. The premutations giving this second type of PRM may perhaps be cytosine‐hydrate in the DNA. Tn average about 23 per cent mutations of B/r are photostable. Since this ratio decreases with low u.v.‐doses in the C‐mutations and increases in P13 and in P16 proba

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08903.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—The wavelength‐dependence ofin vitrophotoreactivation of transforming DNA by yeast extract has been determined. There is an intensity‐dependent lag at the beginning of the biological reaction. There is a similar lag in the splitting of thymine dimers by the yeast extract in the light, a process known to account for most or all of the increase in transforming activity of photoreactivated DNA. The most efficient wavelengths for photoreactivation are around 3550 and 3850 Å. Although the action spectrum is not very similar to flavin absorption, riboflavin at very low concentration inhibits photoreactivation, as it also inhibits a number of flavoenzymes, suggesting that the photoreactivating enzyme might be a flavop

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08904.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—Red light (around 6,550 Å.) and far‐red light (around 7,300 Å) have been administered to excised first internodes of etiolated oat seedlings, and their effects upon growth by elongation have been studied. It has been found that red light inhibits much more the elongation produced bv gibberellic acid (GA) than that produced by 3‐indolylacetic acid (IAA). Far‐red light acts synergistically with GA in promoting elongation, but not with IAA. The effect of far‐red is localized in the node and in the first 4 mm below the node, at least when the seedlings are 63 hr old. The stimulatory effect of the far‐red radiation is observed when seedlings are younger than 65 hr or older than 69 hr after sowing. Except for a gradual decrease with age, there is no such two‐peaked pattern for the sensitivity to red light. Red light promotes the elongation of the node and of the 2 mm‐zone of the first internodes immediately below it. It inhibits the elongation of the zone comprised between 2 and 10 mm below the node. Various types of experiments could not demonstrate a true reversal of the red effect by far‐red light andvice‐versa. They indicated rather an additive effect of the inhibitory and stimulatory properties characteristic of e

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08905.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—Ultra‐violet irradiation of deoxygenated solutions of anthracene, tetracene or pentacene causes the disappearance of the polyacene absorption spectrum and the appearance of an absorption spectrum which is attributed to the photo‐dimer of the polyacene. Molecular structures for ditetracene and dipentacene are proposed, based on that of dianthr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08906.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY

摘要:

Abstract—Although both thymine and uracil can form similar dimers, exposing RNA of tobacco mosaic virus lo ultraviolet radiation of different wavelengths did not reproduce any of the phenomena that implicate dimerization of thymine residues as a major cause of the inactivation of a bacterial transforming DNA. If uracil residues dimerize at all in the irradiated RNA, such dimerization either does not affect infectivity or is not photoreversible in the same way as dirnerization of thymine residues in DNA. Unlike inactivation of the transforming DNA, inactivation of the virus‐RNA seems to be a function of the amount of absorbed radiation energy, irrespective of the wave‐length within the range 285 to 230 mμ and irrespective of a change in the wave‐length during irr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1963.tb08907.x

出版商:Blackwell Publishing Ltd    

年代:1963

数据来源: WILEY