摘要:

Abstract—The electron spin resonances of the metastable triplet states of DL‐5‐hydroxy‐tryptophan, 6‐hydroxynicotinic acid, and other related compounds have been observed in various glasses at 77°K. These compounds are biologically interesting in connection with photochemical processes. The Δm= 2 transitions were observed and the spin‐spin interaction parameter (D2+ 3E21/2 was determined. However, for indole, it was also able to observe the Δm= 1 transitions from whichDandEwere determined separately. From the values of (D2+ 3E2)1/2,DandEwhenever possible and from the decay times of the triplet states, it was possible to characterize the lowest triplets as π—π* states in all cases.Studies of the pH dependence of DL‐5‐hydroxytryptophan, 5‐hydroxyindole, and 6‐hydroxynicotinic acid indicate that the unionized molecule exhibits a resonance different from that of the related ion with a proton removed from the phenolic hydroxyl group.The zero‐field splitting parametersD* and the lifetime of the triplet states have also been measured in various glasses and in Lucite. Both temperature and the specific nature of the host media affected th

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06042.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—Three algal species (Protosiphon botryoides, Chlorella pyrenoidosaandChlamy‐domonas gymnogama) which divide preferentially at night during natural or simulated day‐night conditions are shown to have cell division inhibited by light in the blue region of the visible spectrum (400–500 nm) and stimulated by the remainder of this spectrum (500–730 nm). Synchronous division has been established in cultures of these organisms on a circadian or longer period by alternating fluorescent cool‐white light and cool‐white with the blue component removed. This procedure is suggested as potentially superior to other methods for synchronizing cultures of algae that prefer, in nature, to undergo cell division at night. Where this procedure does not work it is recommended that an action spectrum for cell division be obtained, since this may provide information for achieving optimal synchrony through the use of other specific wavel

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06043.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—Fluorescence lifetimes and absolute quantum yields of a number of chromatographically pure phycobiliproteins have been determined. In conjunction with absorption, fluorescence emission and polarization spectra, these data were used to calculate the number of different types of chromophore, sensitizing and fluorescing, per chromoprotein.To characterize the spatial distributions of the chromophores, the observed emission anisotropies were compared with those calculated from models, using the Förster transfer mechanism and the Jablonski ‘active sphere’ approximation. The experimental values are more consistent with surface locations for the fluorescing chromophores rather than with their distribution throughout the volume.Theoretical efficiencies of transfer between sensitizing and fluorescing chromophores on the same macromolecule are consistent with those observed. The transfer efficiency from phycoerythrin prosthetic groups to chlorophyllacompared with that for transfer via phycocyanin indicates that the latter process is probably the favoured migration

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06044.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The effect of culture conditions on the lethal and mutagenic action of 254 nm (u.v.) and 320–400 nm (b.l.) light has been examined. Ten strains ofEscherichin coliwere used in these investigations. It was found that semi‐dehydration in aerosols greatly enhanced the lethal and mutagenic actions of both U.V. and b.l., Mutations induced by U.V. were found to be of a random kind, while those produced by b.l. were specific and of a particular biochemical type depending on the strain of cell and its stage of development. The presence of oxygen during irradiation enhanced b.l. effects but had no effect on U.V. damage while anaerobic growth endowed the cells with added resistance to b.l. and u.v., Stationary phase cells ofE. coli B/rwere found to be mutated by b.l. specifically at a thymine locus and to be more sensitive thanE. coli Bto the inhibition by b.l. of respiration. Some mutations induced by b.l. inE. coli B/rwere found to hinder the cells ability to carry out the photoreversal of U.V. damage. It is suggested that b.1. affects a specific piece of DNA which is in contact with the cytochrome chain of the cytoplasmic membrane and that this contact point between the cytochrome chain and DNA alters sequentially as the cell proceeds through its life

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06045.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—Anthocyanin synthesis was measured in hypocotyl halves excised fromFagopyrumandSinapisseedlings irradiated unilaterally or equilaterally with red or far‐red light. Although no phototropic curvatures are produced by red or far‐red exposure, a significant gradient in anthocyanin formation was observed forFagopyrumseedlings and the trend for gradient formation is present inSinapisseedlings. The gradient production inFagopyrurnis correlated with this tissue's greater optical density. Since the intensities used do not inhibit elongation completely (through the phytochrome system) and an intensity gradient is present in the tissue (as evidenced by anthocyanin formation) it is concluded that (a) a steeper light gradient is required to induce phototropic curvatures or (b) a diffusible material affecting elongation growth prevents any differential from being established across the t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06046.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The radiative fluorescence lifetimes of the all‐trans, 9 cis and 13 cis retinol, have been measured at various temperatures, and in various solvents. The comparison of these results and of the data calculated from the absorption spectra using the Strickler and Berg equation shows that the transition probabilities are at least one hundred times lower for the radiative emission than for the absorption. Such a discrepancy, which is a general property of the polyenic structure, is closely related to the magnitude of the shift between absorption and fluorescence spectra. We interpret the observed elongation of the radiative fluorescence lifetimes and the temperature dependence of the radiative transitions in the case of all trans retinol as being due to the fact that only the lowest vibrorotational sublevels of1S1, have a reasonable radiative transition probability: the temperature dependence of the radiationless transitions is considered to be due to the existence of a non radiative decay pathway at 550cal/mole above the ‘0

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06047.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY