摘要:

Abstract—Ultraviolet‐sensitive strains ofE. coli, Hs30 (uvr‐phr‐arg‐), lacking the ability to repair ultraviolet damage in the dark (uvr‐), lacking photoreactivating‐enzyme activity (phr‐), and lacking the ability to synthesize arginine (arg‐), and Hs30–R (uvr‐phr+arg‐), having the same auxotrophic marker and the same high u.v.‐sensitivity, were derived, respectively, from resistant strain H/r30 (uvr+phr‐urg‐) and its revertant H/r30–R (uvr+phr+urg‐). Hs30 and Hs30–R have about 25 and 35 times higher sensitivity than H/r30 and H/r30–R for u.v.‐induced killing and mutation to prototrophy, respectively. Efficiency of photoreactivation (PR) of mutation in strain Hs30–R is about ten times higher than the PR efficiency in the parent strain H/r30–R at wavelengths between 3341 and 4358 Å but not that much higher at 3132 Å. On the other hand, Hs30 shows no PR at any of these wavelengths, although the parent strain H/r30 does show PR of mutation around 3341 Å., These results support the. previously described model that PR in H/r30 is an indirect effect of PR light which enhances dark repair. It is concluded that Hs30 and Hs30–R lack dark‐repair capacity for u.v.‐induced mutational damage and that the same type of photoreactivable DNA lesions as those responsible for U.V. killing, i.e. pyrimidine dimers, are the primary cause of u.v.‐induced mutation in theuvr‐strains. PR spectra for killing in Hs30–R and mutation in H/r30–R and H/r30 were obtained and compared, and the quantitative conclusions reached are discussed in connection with the hypothesis that the same kind of lesion (pyrimidine dimer

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05929.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Lag phenomena in the phototactic response ofEuglena gracilisare observed both when the actinic light is turned on and when it is turned off. The on‐lag period is found to decrease exponentially with increasing actinic light intensity. The off‐lag, on the other hand, exhibits a considerably more complex behavior as the light intensity varies. As the temperature is increased above 25°C, the on‐lag period remains constant, whereas below 25°C it increases rapidly. Again, the off‐lag behavior is more complex. Organisms which have been bleached either by growing them in the dark or by exposing them to the antibiotic furadantin exhibit only negative phototaxis. No lag phenomena are observed with these cultures. The mechanistic implications of these results are discussed. Apparently, phototactic accumulation in a lighted region is a dynamic process composed of several component responses. Ultimately, a steady‐state is established in which the rates of in‐ and outflux of organisms are equal. The observed behavior of the lag periods is caused by contributions due to positive topophototaxis as well as negative and positive

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05930.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The major blue pigment from a mutant ofRhodopseudomonas spheroidesthat is unable to grow photosynthetically has been compared with authentic bacteriochlorophyll. By the following criteria the pigments are identical: chromatographic behavior; visible and i.r. epectra of the pigments and of their Mg‐free derivatives in a varity of solvents; reaction in the Molisch phase test; isolation of phytol.The spectrain vivoin the region of bacteriochlorophyll absorption of the following strains grown under a variety of conditions have been compared:(a) wild‐type (strain Ga), (b) photosynthetically deficient mutant (strain PM‐8), (c) secondary mutants derived from PM‐8 lacking colored carotenoid pigments, and (d) carotenoid‐less, photosynthetically competent revertants from strains of type (c). It is concluded (1) that the spectrum of reaction center bacteriochlorophyll (P870) includes an absorption band at 805 mμ as well as at 870 mμ and (2) that the relative heights of the three absorption bands of bulk bacteriochlorophyll (at 805, 850 and 875 mp) are strongly influenced by the pre

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05931.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Precise methods of preparing monolayers and multilayers of chlorophyllaalone or mixed with arachidic acid on glass slides prewated with monolayers of barium arachidate are described in detail. Chlorophyll monolayers obtained by this method are mechanically stable and allow the absorption spectra or other spectroscopic characterizations to be readily made.The data on absorption spectra indicate that uniformly deposited multilayers of over 100 pure chlorophyll a monolayers or over 400 mixed monolayers were obtained. Theabsorbance in the multilayer was directly proportional to the total number of layers. For a given surface pressure used in depositing the multilayers, the absorbance per layer was constan

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05932.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Results from measurements of the absorption spectrum and dichroism suggest that oriented chlorophyll aggregates can be prepared by the monolayer techniques described in the preceding paper.(1)On the longer wavelength side of the major red and blue absorption‐band maxima the absorption decreased with time. For example, the peaks of the difference bands for monolayers prepared under 30 dyn/an were at 443·3 and 703 nm, respectively. The ratio of the red‐to‐blue difference band heights was approximately 1·35. The wavelength position of the red difference‐band maximum is strongly dependent on the surface pressure used in preparing the monolayers. During the decay of absorption, the red‐difference‐band maximum shifted progressively toward shorter wavelengths.The chlorophyll layers showed linear dichroism in some regions of the visible spectrum. The wavelength regions in which maximal dichroism appeared coincided closely with the difference absorption bands. The dichroism disappeared with kinetics similar to those of the absorption decrease.The decrease in the blue and far‐red absorption and dichkoism was taken as evidence that oriented chlorophyll aggregates were formed initially in the monolayers but disaggregated and disoriented with time. Some possible mechanisms for the formation and decomposition of oriented chlorophyll aggrega

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05933.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Light‐induced electron spin resonance (ESR) absorption is not observed in degassed benzene solutions of chlorophyllawith hydroquinone. In the presence of methanol, however, the characteristic hyperfine pattern ofp‐benzosemiquinone ion radical is formed. This photo‐reduction of chlorophyllaby hydroquinone is enhanced apparently by a small amount of triethylamine and inhibited by β‐carotene.Chlorophyll excited in the presence of oxygen produces a single broad ESR signal in benzene solutions which is enhanced by hydroquinone and quenched by β‐carotene, alcohol, and a mine. Their quenching effect is in parallel with their inhibition of the photoauto‐oxidation of chlorophyll. The high quenching capacity of triethylamine for this ESR signal is reduced by the addition of β‐carotene. In methanol solutions, the initial production of the single broad signal is followed by gradual development of the hypertine structure ofp‐benzo‐semiquinone ion radical. This development can be accelerated by triethylamine. The mechanism of these changes is discussed on the primary interaction of excited c

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05934.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Photo‐chemiluminescence is the phenomenon of radiation from a chemiluminescent reaction in which one or more of the reactants are formed initially by a photochemical process. Such photo‐chemiluminest emission has been observed, using a flow apparatus designed for the purpose, in ozne prepared from cylinder oxygen. The emission is shown to be identical with that observed from the reaction of nitric oxide with ozone. The ultimate source of the emission is taken to be the activation in the ozonizer of nitrogen, present as a trace impurity in the oxygen; nitrogen pentoxide is the oxide of nitrogen expected to be formed in the presence of ozone. Photolysis of ozone forms atomic oxygen which reacts with nitrogen pentoxide to yield nitric oxide which subsequently enters into the chemiluminescent reaction with ozone. (Experiments are described which confirm that nitric oxide is one of the products of the reaction between atomic oxygen and nitrogen pentoxide). The variation of emitted intensity with total gas pressure, ozone concentration and linear flow velocity is shown to be consistent with the mechanism proposed.No emission could be detected from either O2(1δg) or O2(1σ+g), which are possible products of the ozone photolysis. It is shown that while the absence of radiation from the1σ+g; state indicates that O2(1σ+g) is not present in our system, yet the apparatus is not sufficiently sensitive in its present form to detect radiation fro

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb05935.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.tb05936.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY