摘要:

Abstract—The formation of thymine dimers in the DNA ofL‐strain mammalian cells after irradiation with ultraviolet light has been demonstrated. The amount of dimer formed rises with the dose of u.v. light.In the course of post‐irradiation incubation the thymine dimers remain in the TCA insoluble fraction and diminish as did the other thymidine‐H3derivatives with increasing incubation time. The dimer is not found in the soluble fraction. Thus, dimer excision (i.e. its liberation into the soluble fraction) as an expression of repair of radiation damage analogous to dark repair inE. coliwas not found in these expe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05806.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—A study of the 518‐mμ light‐induced absorbance change in green cells and a comparison with photosynthetic O2evolution were made. The effect of various chemical agents was also investigated. On the one hand, no antagonistic two‐light effect was observed on the absorbance change, and DCMU had only a partial inhibitory effect on it. On the other hand, it was possible to observe in some cases an indirect kinetic relationship between O2evolution and 518‐mμ change. It is suggested that probably at least two substances absorb around 518‐mμ, one (XI) belonging to system I and another (XII) to system II. The existence and the function ofXIare hypothetical and the identity ofXIIwith the first photoproduct of system II is yet not we

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05807.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Action spectra for light induced sporulation were determined for conidia ofAlternaria dauci, and conidia and perithecia ofPleospora herbarum(Imperfect stage isStemphylium botryosum). Only radiation less than 370 mμ induced formation of conidia, and less than 390 mμ formation of perithecia. The action spectra showed increased effectiveness in the 230 and 290 mμ regions, and possibly in the 260–270 mμ regions. Below 280 mμ these action spectra may not be representative of the “true” absorption spectra of the photoreceptors involved because of possible superimposed effects caused by nucleic acid absorption. Though the action spectra were not identical, the number of characters in common were suggestive of a similar photoreceptor. Similarities between action spectra for sexual and asexual reproduction ofP. herbarumindicate the possibility of a single photoreceptor for bo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05808.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The microsurgical application of a pulsed ruby laser used in conjunction with a multi‐objective microscope is discussed. Some design criteria and various technical and practical problems relating to such use of a laser‐microscope complex are considered. Control of the volumetric energy density at the specimen by means of the instrumentation variables is established on the basis of systematic studies conducted on a stained protein “model tissue”. The instrumentation variables offering the greatest degree of control are the beam energy, the objective focal length, and the degree of defocusing of the laser beam. Results of the “model tissue” study enable one to predict in advance the size and severity of destructive effect that will be produced in thin layers of green plant tissue using a particular combination of variables. A judicious extension of these results enables single cell and intracellular microsurgery to be performed with precision. In addition, various biological tests and experiments were conducted in order to determine the applicability of a laser‐microscope system to biological research and to delineate

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05809.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Protection by acridine orange against ultraviolet light effects in resting cells ofE. coliB/r/1, try‐was studied with special reference to a possible oxygen effect. Dose‐response relationships were described by the functionS= 1–(1 ‐e‐kD)nwhereSis the surviving fraction andDis the u.v. dose in ergs/mm2. For cells suspended in 5 × 10‐‐6M acridine orange (AO) in air, the radiation sensitivitykwas reduced from 0.010 (ergs/mm2))‐1in the absence of the dye to 0.0053 (ergs/mm2)‐1in the presence of the dye. Under anoxia at this AO concentration,kwas further reduced to 0.0015 (ergs/mm2)‐1. The oxygen effect ratio,kO2/kN2, was 3.5 at this concentration of AO. Greater protection was observed in cells suspended in 2 × 10‐‐5M AO, the oxygen effect ratio was unchanged. No oxygen effect was detected in the u.v. response in the absence of the dye. The value ofnwas reduced from about 12 with no dye to about 5 at dye concentrations of 5 × 10‐‐6M AO or more when oxygen was present. Under anoxia, in the presence of AO,nwas further reduced to about 1.3. Atebrin, an efficient u.v. protective agent but an inefficient photodynamic agent, had no oxygen effect for protection against u.v. inactivation. Acridine orange protected against u.v.‐induced reversion to tryptophan indepence inE. coliWP2 to about the same extent as it did for inactivation. A similar oxygen effect was observed for

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05810.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The excitation spectrum for bacteriochlorophyllbfluorescence, the action spectrum for cytochrome‐553 oxidation, and the action spectrum for P‐985 bleaching are compared to the absorption (1‐T) spectrum of aRhodopseudomonassp. NHTC 133 extract over the range 770 to 930 mμ. These spectra show that a minor pigment P‐830 is more effective in sensitizing cytochrome oxidation and P‐985 bleaching than in exciting fluorescence of Bchlb. These results are consistent with the proposal that P‐830 is a form of Bchlbin special relation to the reaction center

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05811.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Purple photosynthetic bacteria contain a component, absorbing near 805 mμ, distinct from the major light harvesting bacteriochlorophyll component. The minor component, designated P800, resembles P870 in that it resists oxidative treatments that destroy the light harvesting bacteriochlorophyll. Light induces a reversible blue‐shift of P800 together with the reversible bleaching of P870. The ratio of P800 to P870 inRhodopseudomonas spheroidesis constant. Both pigments are absent in phenotypes that cannot grow photosynthetically; they reappear together in revertants to photosynthetic competence.Action spectra for light‐induced bleaching of P870 and for bacteriochlorophyll fluorescence show that P800 transfers energy more efficiently to P870 than to the bulk bacteriochlorophyll.It is concluded provisionally that P800 is a specialized bacteriochlorophyll molecule in close proximity to the reaction center componen

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05812.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Chromatophores fromRhodopseudonionas spheroideswere treated with potassium iridic chloride so as to destroy the major complement of bacteriochlorophyll (BChl) without harming the photochemically active P870. A band at 802 mμ, attributed to a pigment P800, survived this treatment along with P870. Extraction of such chromatophores with a mixture of acetone and methanol removed the absorption bands of P800 and P870; a corresponding amount of BChl was found in the extract. The yield of BChl was too great to have been derived from either P800 or P870 alone; analysis of extinction cofficients and band areas of these pigments indicates that they are both specialized fornis of BChl, in a molecular ratio of 2P800:1P870.Bleaching of P870, without attenuation of the absorption band of P800, could be effected by adding potassium ferricyanide to the iridic chloride‐treated chromatophores. Extraction of chromatophores in this condition gave a reduced yield of BChl, consistent with a 2:1 ratio of P800 to P870 under the assumption that the BChl in the extract was derived in this case from P800 alone.An absorption band at 600 mμ in iridic chloride‐treated chromatophores, characteristic of BChl and ascribed to P800 and P870, is partly bleached and shifted to shoiter wavelengths upon illumination. This reversible effect, and a similar one near 375 mμ (corresponding to the Soret band maximum of BChl), has the combined attributes of the blue‐shift of P800 and the bleaching of P870 seen in a spectrally resolved form near 800 and 865 mμ respectively. The 600 mμ band is bleached by about 30 per cent, again consistent with a ratio of 2P800:1P870.These data, in conjunction with information published elsewhere, support the view that two molecules of P800 and one of P870 are associated jointly with a photosynthetic reaction center.It was observed that the long wave absorption bands of BChlin vivoare sometimes narrower than the narrowest bands that have been observed for BChl in dilute organic solutions. Sharpness of these bands is most conspicuous in some forms absorbing

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05813.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—In the photosynthetic bacteriaChromatium, Rhoahpirillum rubrum, andRhodopseudomonus spheroidesthe fluorescence of bacteriochlorophyll is probably free of contamination by a “fast” component of delayed emission, judging from the characteristics of the delayed light measured 3 msec after excitation.InRps. spheroidesthe pigment P870, associated with photochemical reaction centers, is non‐fluorescent in its photochemically active state. Fluorescence of P870 can be induced by either of two agencies that suppress its photochemical activity: exposure to Na2S2O4and (in a dry chromatophore film) dessication.The yield of fluorescence from the major (light harvesting) component of bacteriochlorophyllin vivois brought to a common maximum value by conditions that suppress the photochemical activity of P870. In addition to dessication and exposure to Na2S2O4these conditions include saturating illumination and exposure to K3Fe(CN)6. Of these four treatments only the last two bleach the long wave absorption band of P870.These experiments support the following assertions:(1) P870 traps singlet excitation energy absorbed by the light harvesting BChl; the trapping function of P870 depends on its ability to initiate and participate in photochemistry.(2) Both dessication and exposure to Na2S2O4suppress the photochemical activity of P870 by blocking an event that proceeds directly from the excited singlet state in P870.(3) The fluoresecence of BChlin vivois emitted almost entirely by a major (light harvesting) co

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05814.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05815.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY