摘要:

Abstract—The effect of photocrosslinkings4U8withC13on the structure ofE. colitRNA has been examined by high resolution NMR. Photocrosslinking affects both the structure and the enzymatic acylation of tRNA. The NMR measurements demonstrate that except for thes4U8.A14base pair, there is no evidence that photocrosslinking perturbs any of the common tertiary structure interactions. However, this modification does perturb several resonances which are assigned to the secondary structure base pairs of thehUstem and the terminal base pair of the acceptor stem. The variable effect of photocrosslinking on the extent and rate of enzymatic acylation of different tRNA is attributed to different recognition sites for tRNA by the cognate synthetase

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07458.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—…An analysis of the photophysical and theoretical properties of e‐adenine and the RNA Y‐base shows that these materials have a closer conceptual relationship to the indolizines than the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07459.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—…Highly resolved fluorescence spectra of chlorophyll‐aand ‐bhave been measured in ethanol and methyltetrahydrofuran glasses at ˜4K. The vibrational frequencies measured are independent of solvent and were highly reproducible, ±1cm‐1or less. A possible use of this experimental technique as an analytical tool i

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07460.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—…According to the criteria of enhancement in D2O and inhibition by sodium azide, the oxidation of tyramine photosensitized by methylene blue is largely a singlet oxygen or Type II process. Its quantum yield approximates 0.3 in D2O at pH 10. There is a less efficient reaction not quenched by azide, which is assigned to a dye‐substrate or Type I process. It gives rise to products with distinct bands at 320 and 285nm. Products of the Type I reaction are further oxidized by singlet oxygen and thereby compete with tyramine for this reagent. Kinetic parameters were estimated by computer simulation of the dependence of quantum yield on extent of reaction. The rate constant for reaction of O2(1Δg) with tyramine was estimated to be 2.8 × 108M‐1s‐1± 20% at pH 10. The reaction was also sensitized by hypericin in what appears to be a Typ

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07461.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—…Ultraviolet (UV) micro‐irradiation of the cell nucleus was used to study RNA synthesis. CV‐1 cells in culture were irradiated in the nucleoplasm in an area of 5 µm in diameter, with UV doses of the order of 10 and 102Jm‐2at 254 nm and pulsed with3H‐uridine (3HU) 1 h and 24h after irradiation. Parallel cultures were irradiated under the same conditions and labeled with3H‐thymidine (3HTdR) to measure unscheduled DNA synthesis (UDS).For the two incident doses used, 1h after irradiation, RNA synthesis was decreased over the whole nucleus by 50% compared to unirradiated control cells. Moreover, for irradiation with 102Jm‐2,3HU uptake was completely inhibited in the irradiated spot; UDS occurred only in the irradiated area. At 24h after irradiation,3HU uptake occurred over the whole nucleus in the same amount as in non‐irradiated cells. At this time, UDS was undetectable. These studies indicate the occurrence of a repair process leading to a recovery of the function of transcription, and suggest the role of pyrimidine dimers in the inhibitio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07462.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—…Previous work has demonstrated that fluorescent material (360nm excitation, 440nm emission), whose concentration normally increases with age in human lenses, can be generated artificially by exposing cultured human or animal lenses to UV radiation. In the present paper we report measurements of the rate of production of this fluorescent material in rat lensesin vitroas a function of UV irradiation wavelength. A plot of the observed rate of fluorogen production normalized to constant photon flux vs irradiation wavelength shows little action at 360 or 320nm, increases sharply at 300nm, remains relatively constant in the range 300–280nm, and then exhibits a further gradual rise from 270–250nm. The results on rat lenses are compared with results reported elsewhere for tryptophan in aqueous solution. The action spectrum for photochemical destruction of tryptophan in solution closely parallels that for fluorogen production in rat lenses. This result and other evidence suggest that photochemical destruction of tryptophan might be the initial event in UV‐induced fluorogen production in the oc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07463.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—…Phototransformations of the red/far red reversible plant pigment phytochrome involve several intermediates. At 77K,lumi‐F, the initial product of phototransformation of the far red absorbing formPfrand some of its relaxation products are shown to undergo further phototransformations.Lumi‐Fhas an absorption maximum in the region 690–730nm. The product, giving rise to a maximum in the difference spectra at 650nm, formerly thought to belumi‐F, is now believed to represent one of its relaxation products. The nature of the reactions connecting these various intermediates ar

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07464.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—…The ac admittances of metal I chlorophyll a|Hg sandwich cells are shown to depend upon the chlorophyll (Chi) layer thickness, the aggregation state of the Chi, the light‐dark environment of the cells and the nature of the metal. The results suggest the presence of different but not independent charge transport processes in these cells. One process gives rise to a broad dispersion in the frequency dependent capacitance and conductance. This process is observed in all cells and is most readily ascribed to a hopping or tunneling of charge carriers across potential energy barriers. Another mechanism which is detected only with crystalline Chi and only with certain metal substrates is ascribed to interfacial polarization. A model circuit incorporating these interpretations yield calculated admittance data which approximate those measured experimen

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07465.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Abstract—…After a short‐term solubilization with sodium dodecyl sulphate, chloroplast membranes of tobacco were separated by polyacrylamide gel electrophoresis into three chlorophyll‐protein complexes. In addition to the two major complexes termed I and IIccorresponding respectively to P700 chlorophylla‐protein and light‐harvesting chlorophylla/b‐protein described by Thornber (1975), a relatively stable complex termed IIahas been observed. This new complex has an apparent molecular weight of 70,000 daltons and possesses Chlaandb.Complexes I, IIaand IIChave been isolated and precise spectroscopic analyses have been performed. Fourth derivative analyses of low temperature absorption spectra suggest that complex IIaseems more representative than IICof chlorophyllaforms present in intact thylakoid membranes.Moreover, the electrophoretic study reveals that CPIand CPIIare composed of only one polypeptidic subunit with respective molecular weights of 68,000 and 2

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07466.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryUpon irradiation with 240–300nm light a photochemical reaction occurs in Tb3+complexes of polyuridylate and oligouridylate. The reaction is monitored by the appearance of a fluorescence excitation band which does not exist in non‐irradiated samples. The photochemical reaction is not observed in uridine nucleotides, dinucleoside phosphates, or when polyuridylate forms a double stranded helix with polyadenyl

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1977.tb07467.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY