摘要:

Abstract—Ultraviolet‐irradiatedE. coliDNA (3H‐thymine‐labelled) was mixed with un‐irradiatedE. coliDNA (14C‐thymine‐labelled) and exposed to light in the presence of purified yeast photoreactivating enzyme. As the3H‐thymine‐containing cyclobutane dimers disappeared during the photoreactivation, there was a stoichiometric increase of monomeric3H‐thymine as determined from the3H/14C ratio in thymine. This is the first direct demonstration that thymine‐containing dimers in u.v.‐irradiated DNA are monomerized by yeast photoreactivating enzyme i

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08794.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—The anaerobic photobleaching of 6, 7‐dimethyl‐9‐(2′‐hydroxyethyl)‐isoalloxazine, 9‐(2′‐hydroxyethyl)‐isoalloxazine and 6,7‐dimethyl‐9‐(formylmethyl)‐isoalloxazine have been compared. Polarographic and spectrophotometric techniques were used for rate studies. The methyl groups on the aromatic ring at the 6 and 7 positions affects the product distributtion in these simple flavins. Formylmethylflavin is postulated to undergo a bimolecular photoredox reaction which is novel to flavin photochemistry. It was demonstrated that there is a common type of leucoflavin formed during anaerobic photobleaching of riboflavin, formylmethylflavin and hydroxyethylflavin. This leucocompound also formed during the photoreduction of formylmethylflavin but not during the photor

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08795.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—The anaerobic photolysis of the flavins containing hydroxyethyl and formythmethyl side‐chains in place of the ribityl group of riboflavin has been studied employing spectro‐photmetry, thin‐layer chromatography and other mehtods. Both flavins are shown to decompose, in part, directly to lumichrome. Acetaldehyde arises from the hudoxyethyl by the flavin nucleus as has been observed previously for riboflavin. The side‐chain of the hydroxyethylflavin, is shown to be oxidized to the formylmethyl group. Formylmethylflavin is converted in part to lumichrome and unknown products from the side‐chain and in part to a reduced flavin. Formaldehyde could not be detected among the products. Possible mechanisms are discus

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08796.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—Flavines in the excited state can effect anaerobic oxidation of amino acids to keto acid and ammonia. The rate of the process depends on the structure of the amino acid. These systems show similarities to the amino acid oxidase

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08797.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—We have investigated the effects of solvent and pH on the absorption and emission propertied of various 6‐ and 9‐substituted purines as a means of examining the nature of the directed not only at deteriming the relative energies of (π,π*) and (π,π*) states, but in particular, at examining the nature and energies of the two lowest‐lying (π,π*) states. For examplem, the attachment of a methyl or ribosyl group to the N9 of purine does not change the relative energies of the lowest‐lying (π,π*) and (π,π*) states; thus, the latter is the singlet of lowest energy. However, the lowest singles in derivatives formed by substitution at C6 are(π,π*) states—i.e. there is no long‐wavelength tail in the absorption spectra and florescence is comparable in intensity to phosphorescence. Further the absence of emission from neutaral adenine at room temperature is due to temperature quenching. Both lowest (π–π*) transtions. are contained under a common envelope and cannot be resolved in the absorption spectra. The shoulder observed in some of these compounds on the long‐wavelength slope of absorption envelope is vibrational in nature. Consideration of the effects of solvents on absorption and the analysis of luminescence spectra make it possible to locate the relative position of these (π–π*) transitions within the common envelope. In compounds with an ‐H on N9 and a free (aza) N1 (e.g. adenine, anionic hupoxanthine) the weaker, solvent‐sensitive (W) band has a higher energy then the more intense, solvent‐insensitive (S) band. When N1 is protonated, (e.g., in hypoxanthine or cationic adenine) and/or when methyl or ribosyl is substituted at N9, the order of these bands is inverted due ot a red shift of theWband. This shift is most apparent in the 9‐substituted hypoxanthines, where in non‐polar solvents theWband can be readily resolved in the absoption spectra. This inversion results in a red shift of both fluorescence and phophorescence and an increase of theP/Fratio. When chlorine or iodine is attached at C6 only phosphorescence having a very short lifetime appears due to heavy a

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08798.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—The polarization of fluoresecnce and phosphorescence due to the emission from (π,π*)singlet and triplet states of purine and several of its derivatives have been measured using the method of photoselection. In at least two 2‐amino substituted derivatives, the two lowest π‐π* transition moments are mutually perpendicular. The main vibrational progression of phosphorescence is negatively polarized with respect to both of them and therefore must be singlet states interact with the emitting (π.π*) triplet state. In addition a weak progression, polarized in the plane of the molecule, is found. The vibronic mixing of (n,π*) and (π,π*) triplet states is suggested to account for the mixed polarization. The halogen derivatives of purine show zero plarization of phosphorescence and their phosphorescence spectra are blurred so that it is difficult to differentiate the various inte

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08799.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—Chloroplast fragments obtained after treatment with a non‐ionic detergent (Triton X‐100) are studied spectroscopically. Their absorption and fluorescence spectra show the possibility of obtaining separately, without any visible alteration, the two groups of chlorophyll holochromes corresponding to the two photochemical systems. One of the chloroplastic fractions, enriched in chlorophyll‐bshows, like whole chloroplasts, an oxygen burst upon illum

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08800.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08801.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY