摘要:

Abstract—–Quantum efficiencies have been measured for the photoisomerization of four stereoisomers of retinal (all‐trans, 13‐cis, 11cis, and 9‐cis) in two solvents at different wavelengths of irradiation and at various temperatures. In heane at 25°C the quantum efficiencies for isomerization at 365 nm are: 9‐cistotrans, 0.5; 13‐cistotrans, 0.4; 11‐cistotrans, 0.2; all‐transtomonocisisomers, 0.2‐0.06, depending upon assumptions made regarding the stereo‐isomeric composition of the product. These values vary somewhat with the wavelength of the irradiating light.The quantum efficiency for the photoisomerization ofall‐transretinal in hexane decreases by a factor of 30 when the temperature is lowered from 25° to – 65°C; the activation energy for this photoisomerization is about 5 kcal/mole. The quantum efficiencies for the isomerization of themonocisisomers toall‐transretinal in hexane are virtually independent of temperature. In ethanol the rates of photoisomerization fromtranstocisorcistotransdepend only slightly on the temperature between 25° and – 65°C.The photosensitivities of the stereoisomers of retinal are of the same order of magnitude as those of the retinylidene chromophores of rhodopsin (11 ‐cis), metarhodopsin I (all‐trans), and isorhodopsin (9‐cis); but it is not yet possible to derive the photochemistry of rhodopsin uniquely

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06057.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—–The Planck law relationship between absorption and emission spectra is applied to the spectral sensitivity curve of human rod vision, assumed to be equivalent to the absorption spectrum of the visual pigment rhodopsin, to compute a hypothetical emission spectrum for rhodopsin. When 17, 100 cm‐1is used as the reflection axis, the mirror image of this hypothetical emission substantially matches the activation spectrum over 2500 cm‐1. The predicted emission increases exponentially at long wavelengths, in contrast to published observations of fluorescence at 580 nm; this discrepancy, and an estimate of excited state lifetime based on the Planck law theory, suggest that emission occurs from a meta‐stable vibrationally‐excited state. The exceptionally slow falloff in absorption at long wavelengths is explained as being due to the smaller dependence of potential energy on angle of twist about bonds in the polyene chain in the lowest π, π* singlet state of rhodopsin than in its ground state; a model assuming six or seven essentially flat vibronic modes in the excited state accurately fits the observed ac

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06058.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—–An attempt was made to identify some of the ultraviolet (u.v.) photoproducts of 5‐bromouracil‐labeled DNA (BrU‐DNA). Two synthetic dinucleotides, 5‐bromodeoxyuridylyl‐(3' →5 ')‐thymidine (BrdUpT) and 5‐bromodeoxyuridylyl‐(3' → 5')‐deoxycytidine (BrdUpdC), were prepared. Each gave a single u.v. photoproduct which in turn gave a single acid hydrolysis product. 2‐14C‐BrU‐DNA. prepared fromE. coliB3, was irradiated (275–280 nm), hydrolyzed, and paper chromatographed in four systems. Comparison with the two synthetic photoproducts showed that if present at all, BrdUpT and BrdUpdC photoproducts could account for no more than 10 and 3.5 per cent respectively of the total photoproducts. At 55 per cent conversion of BrU into photoproducts, the major14C‐photoproduct was uracil (78 per cent); the remaining 22 per cent was made up of at least six products, three of which were reversed by 232 nm irradiation.The debrominated cyclobutane structure proposed by Haug for BrdUpT photoproduct has been shown to be incorrect. It was found to contain one atom of bromine per molecule. On the basis of nuclear magnetic resonance and u.v. spectra, two possible structures are proposed for the photoproduct, eac

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06059.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—–Lethality in a repairable strain (WP2) and an excision repair deficient strain (WP2hcr) ofEscherichia coliwas studied at wavelengths of 254, 313, 365, and 390–750 nm. Survival curves were empirically fitted to the expressionS= 1 ‐ (1‐e‐kl)“, whereSis the fraction surviving,Dis the incident dose in ergs mm‐2,kis the inactivation constant in units of (erg mm‐2)‐1andnis the ‘shoulder constant’. The repairable sector (k(hcr‐)–k(hcr‐)lk(hcr‐), a conservative estimate of the repair capability ofE. coliWP2, was 0.91 at 254 nm, 0.92 at 313 nm, 0.60 at 365 nm, and 0.13 at 390–750 nm. Although there was no oxygen enhancement of inactivation at 254 nm and 313 nm, a strong enhancement was identified at 365 nm and 390–750 nm. These results suggest that oxygen‐dependent damage induced by near u.v. (365 nm) can be partially repaired by

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06060.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—–The influence of temperature, pH, salts, and reactant concentrations on the biolumin‐escent oxidation ofCypridinaluciferin catalyzed byCypridinaluciferase indicates a highest quantum yield φ (einsteins per mole of luciferin oxidized) of 0.31 in H2O, or 0.33 in 99% D2O. With the aid of data on fluorescence of the light‐emitting oxyluciferin‐luciferase complex, and of oxyluciferin in diglyme, partial explanations are suggested for the observed variations in φ, including the relatively low φ, of 0.03 for chemiluminescence of luciferin in organic solvents, wherein a different pathway of luciferin degradation, as indicated by chromatographic evidence, results in much less population of the e

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06061.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—–Absorption and emission spectra of Schiff bases of pyridoxal‐HCI or pyridoxal‐5‐phosphate with L‐valine,n‐butylamine or N‐α‐acetyl‐L‐lysine‐N‐methylamide have been studied as a function of pH. We can write the complete ionization diagram and equilibria. The results of Martell[6] are confirmed: the forms analogous to the coenzyme in aspartate aminotransferase, which absorb at 410 nm and 360 nm (or 340 nm for the Schiff base with n‐butyl‐amine) have the phenol OH ionized; the imine nitrogen is protonated for species absorbing at 410nm (in the enzyme: inactive form and complex with aminoacid) and unprotonated for species absorbing at 360 nm (in the enzyme, active form). Their fluorescence wavelengths are respectively 500 nm and 430 nm. Protonation of the pyridine nitrogen of these forms does not shift the absorption band; the fluorescence intensity is 20‐fold greater for the N‐protonated forms.The realpKof the imine nitrogen is 8.5 ±0.8 for species with pyridine N‐protonated or 10.4 for the non‐protonated forms. The observedpK6.3 in the enzyme can be explained if the imine nitrogen is hydrogen bonded to an amino‐acid side chain of the protein: lysine, tyrosine, serine, sulfhydryl.The quantum yield of the coenzyme fluorescence in the enzyme has been compared to that of the analogous Schiff base (absorbing at the same wavelength). According to the results, we cannot deduce whether the pyridine nitrogen is protonated in pyridoxal form of the enzyme.If it is protonated, as in the pyridoxamine form, the coenzyme environment is not the same in the two forms. If the pyridine nitrogen is unprotonated in the pyridoxal form and protonated in the pyridoxamine form, the environment of the coenzyme is

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06062.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—–By e.s.r. we have studied the photoexcitation of an aromatic amine to its triplet state at 77°K, its photoionization to a radical cation and the simultaneous formation of solvent radicals proceeding from the photosensitization of the organic glassy matrix.In the case of methanol and ethanol matrix we observe approximately one solvent radical per solute radical cation. In the case of isopropanol and methyltetrahydrofuran we find respectively three and two solvent radicals per solute radical cation. The results suggest two possible processes of photosensitization. By successive absorption of two photons, the amine reaches an excited triplet state which is able either to dissociate giving one electron and one cation radical or to transfer its energy to the solvent, this last being decomposed.It is assumed that in the case of methanol and ethanol, the radicals from the solvent are only formed by reaction on the matrix by the released electron, whereas in the case of isopropanol and methyltetrahydrofuran, the second process is prevalent or exclu

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06063.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06064.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—–Carotenoids, with II conjugated double bonds show a lack of fluorescence. For β‐carotene, no U.V. fluorescence (300–400 nm) is observed with a quantum yield greater than 10‐4we have observed a large hand visible fluorescence, already described by several authors, but this fluorescence remains when the β‐carotene is bleached, and must be assigned to some impurity present with β‐carotene. The fluorescence of lycopene solutions, whose quantum yield should be smaller than 10‐3, is similarly assigned to an impurity less photosensitive than lycopene. The fluorescence of canthaxanthine is also very weak (quantum yield ˜ 2. 10‐5). In the deactivation paths to the ground state, photodecomposition is quite unimportant, and probably photoisomerisation too: internal conversion appears to be extremely rapid, within a time scale comparable with the periods of vibratio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06065.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb06066.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY