摘要:

Abstract—The fluorescence decay profiles, relative quantum yield, and transmission of the phycoerythrin a subunit, isolated from the photosynthetic antenna system ofNostocsp., were measured using single picosecond laser excitation. The fluorescence decay profiles were found to be intensity independent for the intensity range investigated (4 × 1013and 4 × 1015photons‐cm‐2per pulse). The decay profiles were fitted to a model assuming both chromophores absorb and fluoresce. The inferred total deactivation rates for the two chromophores, in the absence of energy transfer and when the effects of the response time of the streak camera and the finite pulse width are properly included, are 1.0 × 1010s' and 1.0 × 109s1for the s and f chromophores. respectively, whereas the transfer rate between the two fluorophorcs is estimated to be 1.0 × 1010s−1giving a s→ f transfer rate on the order of (100 ps)−1. Steady‐atate polarization measurements were found to be equal to those calculated using the rate parameters inferred from the kinetic model fit to the fluorescence decays. The apparent decrease in the relative fluorescence quantum yield and increase of the relative transmission with increasing excitation intensity is suggestive of ground state depletion and upper excited state absorption. Evidence suggests that exciton annihilation is absent within isolated α subunits for the intensity range investigated (4 × 1013to 4 × 1015

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05593.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—Phycocyanin 645, phycocyanin 612 and phycoerythrin 545 are biliproteins isolated from the cryptomonad algae,Chroornonasspecies,Hemiselmis virescensandRhodomonas lens, respectively. The protein has α and β subunits. which are separated on an ion exchange column by using a urea gradient and omitting 2‐mercaptoethanol from the solvent. This separation establishes that the α and β subunits are not joined by disulfide bonds. In addition it has recently been shown that mercaptoethanol can produce spurious results in the calculation of the chromophore contents of these biliproteins (Guard‐Friar and MacColl, 1984). The mercaptoethanol‐free experiments allow analysis of the chromophore content in a rapid and artifact‐free manner. When the ion exchange chromatography of phycocyanin 645 is manipulated by changing the type of urea gradient, two distinct a subunit fractions are obtained. These two fractions have identical visible absorption spectra but different amino acid compositions. At least two different gene products are, thus. responsible for the a subunits. The sole chromophore on the two a subunits of phycocyanin 645 is the unique 697‐nm bilin as seen in acidic urea. Its reactivity with mercaptoethanol is determined. The α subunits of phycoerythrin 545 have two different bilins: cryptoviolin and phycoerythrobilin. Phycocyanobilin is the chromophore on the α subunit o

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05594.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—Pre‐irradiation of stationary phase cells ofEscherichia coliK‐12 with broadband near‐UV radiation potentiates the lethal effects of subsequent exposure to near‐UV radiation plus hydrogen peroxide. Identical fluences failed to modulate killing due to far‐UV radiation. These data indicate that biologically revelant levels of hydrogen peroxide may be generatedin situupon the near‐UV irradia

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05595.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—Reactions involving singlet oxygen and other free radicals have been identified in epidermis containing either exogenous or endogenous photosensitizers. soaked in a singlet oxygen/free radical trap, and then exposed to visible or UV‐A (320‐400 nm) light. Such reactions can be quenched by the presence of the carotenoid pigments β‐carotene and canthaxanthin which accumulate in epidermis after oral administration. We report here that the carotenoid pigments β‐carotene. canthaxanthin and phytoene accumulating in epidermis can also quench to some degree those photochemical reactions involving singlet oxygen and free radicals that occur when epidermis is exposed to the sunburn spectrum of light (UV‐B

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05596.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—A new ultra‐low‐light level camera svstem has been developed to detect a single photon. Operation principles and some characteristics are pres

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05597.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05598.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1986.tb05582.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY