摘要:

Abstract—The emission spectra of human adult hemoglobin A0and its isolated α and ß subunits were obtained using a highly sensitive photon‐counting spectrofluorometer. The quantum yields of the emissions, relative to free tryptophan, were also measured as well as the excitation polarization spectra for hemoglobin A0and apohemoglobin. The fluorophore bis‐ANS was utilized to probe for the presence of apoproteins in the hemoprotein preparations. The work suggests that tryptophan may be useful as an intrinsic probe to study dynamical processes in hem

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03674.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Low‐temperature (and some room temperature) absorption and emission, fluorescence and phosphorescence, data including quantum yields and lifetimes have been obtained from the title pyrimidine bases as a function of the nature of the solvent environment. Modest vibrational resolution has been observed for the first time in the absorption spectra, particularly for thymine and uracil. The excitation spectra also show structure. The quantum yields of fluorescence (φF) and phosphorescence are independent of the excitation wavelength. Thymine, thymidine and uracil have profoundly different photophysical properties in polar‐aprotic vs polar‐protic solvents. The N, N‐dimethyl substitution of thymine and uracil produces photophysical changes comparable to the solvent change for the unsubsti‐tuted bases. The species involved in the emission processes is the keto (lactam) form. It is probable that1,3(n,π*) state(s) has(have) changed order relative to a lowest1(π,π*) state as a consequence of both the solvent change and N, N‐dimethyl substitution. The lowest triplet state is assigned as3(n π*). We propose that an important factor contributing to the previously reported excitation wavelength dependence of φFand φT1(φisc) for nucleic‐acid components is the equilibrium coexistence of H‐bonded and non‐H‐bonded forms each having different photophysical properties. Consideration is given of the impact of the significantly different photophysical properties of nucleic‐acid bases as a function of the nature of the solvent up

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03675.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—The steady‐state intensity and lifetime of the tryptophan phosphorescence from a number of globular proteins in 2:1 (v/v) glycerol buffer were monitored as a function of temperature. The phosphorescence lifetimes are essentially independent of the tryptophan local environment in rigid solution at temperatures<170K, but vary markedly between proteins at temperatures at which the solutions become fluid. The ratio of steady‐state intensity to lifetime P/τ was found to be temperature independent despite the quenching for free tryptophan and the lone residue in myelin basic protein. Heterogeneity in the triplet quenching of the tryptophans in liver alcohol dehydrogenase and alkaline phosphatase were revealed as step‐like decreases in the ratio of P/T followed by plateau regions characterizing the homogeneous behavior of the more resistent tryptophans in the proteins. This heterogeneity exists not only between solvent‐exposed and buried residues, but reflects variations in the flexibility of the structure surrounding distinct buried tryptophans in the globula

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03676.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—On unsensitized photooxygenation magnesiummeso‐tetraphenylporphyrin underwent oxidative ring cleavage yielding a bilitriene derivative as the sole product. Kinetic studies by quenching technique using singlet‐oxygen quenchers, ß‐carotene and α‐tocopherol, and by substrate direct disappearance technique (Foote and Ching) indicated that only singlet‐oxygen process is involved in the photooxygenation, and that the rate of total consumption of singlet oxygen (kQ+kR) is 1.0 ± 0.4 t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03677.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—The optical properties of a polymer film which incorporates the photosensitising drug, nalidixic acid, as the chromophore are described. The film is shown to be suitable as a UV dosimeter in the wavelength range 280–350 nm. It is suggested that the film could be used as a biological monitor in subjects photosensitised with 8‐methoxypsoralen. as in the photochemotherapy of psor

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03678.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—The production of UV‐induced thymine dimers and their fate upon post‐irradiation incubation in the dark was studied in DNA of the intact water plantsWolffia microscopicaandSpirodela polyrhiza.The results demonstrate production of thymine dimers, and the ability of the plant cells to remove the dimers from their DNA. The rate of removal is rapid during the first few h of post‐irradiation incubation in the dark. It continues at a slower rate for the next 24–48 h, at which time it is essentially complete. The disappearance of thymine dimers in light or in the dark is analogous to the well‐known processes in other biological systems, namely, photoreactivation and da

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03679.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—The induction of mutations (reversion to tryptophan independence) by various UV (254, 313, 334 and 365 nm) and visible (405 and 434 nm) wavelengths was measured in exponential phase populations ofEscherichia coliB/rthy trpand B/rthy trp uvrAby assay of irradiated populations on semi‐enriched media. No mutations were induced in the repair proficient strain at wavelengths longer than 313 nm. Mutations were induced in the excisionless strain at wavelengths as long as 405 nm but less than expected from the known amount of DNA damage induced. Irradiation at the longer wavelengths (434, 405, 365 and 334 nm) suppressed the appearance of 254‐ or 313‐nm‐induced mutations in the repair competent strain but not in the excision deficient strain. The relative dose‐requirement for mutation suppression was related to the relative efficiency of these wavelengths in inducing growth delay. These results suggest that the growth delay induced by near‐UV and visible wavelengths allows more time for the ‘error‐free” excision repair process to act on the potentially mutagenic lesions induced by 254‐ and 313‐nm radiations, thereby reducing the mutation frequency observed in the repair‐proficient strain. The level of near‐UV mutation induced in the excision deficient strain is lower than expected from the DNA damage known to be induced. It is possible that near‐UV radiation induces a class of lethal lesions that are not susc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03680.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—MDV‐1 RNA is a small variant of bacteriophage Qß, and consists of complementary ‘plus’ (+) and ‘minus’ (‐) strands. It is an active template in replication reactions catalyzed by Qß replicase. Using high‐resolution polyacrylamide gel electrophoresis, we have located the sites of replication inhibition caused by irradiation of (+) and (‐) MDV‐1 template RNA with 254‐nm light. Presumably, this inhibition was caused by uridine hydrates and pyrimidine cyclobutane dimers, which previously were shown to be formed at levels of 3.5 and 0.3 per (+) MDV‐1 strand, respectively, at the dose used here (2500 Jm‐2). Each of the ten inhibition sites correspond to regions in the template which contain two or more pyrimidines, including at least one uridine. At each site, replication inhibition occurred at two or three adjacent bases. The sites of the photolesions with respect to the known primary sequence and proposed secondary structure of MDV‐1, and the implications of this work for locating the sites of lesions produced by other agents which inhibit the replication of a sma

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03681.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—The action spectrum for growth delay induced by near‐uv light was determined forEscherichia coliB/r growing in a defined medium. This spectrum agrees with and extends that determined earlier by Jagger and his co‐workers forE. coliB growing in nutrient broth. The extended spectrum is indistinguishable from the absorption spectrum for 4‐thiouridine above 320 nm, but deviates significantly at wavelengths shorter than this from the spectrum for 8–13 link formation in transfer RNA containing 4‐thiouridine at position 8. These results extend the evidence that 4‐thiouridine in transfer RNA is the chromophore for near‐UV induction of growth delay, but weaken the case for linkage of a pyrimidine at position 13 in transfer RNA as the mechanism

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03682.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—We present an improved analytic characterization of diffuse spectral irradiance (skylight) for the wavelength range 280–380 nm and solar zenith angle range from 0 to 85°. The formulas achieve greater accuracy by (a) focusing on ratio representations and (b) adjusting the parameters to the more precise radiative transfer calculations of Dave, Braslau and Hal

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1980.tb03683.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY