摘要:

Abstract—An action spectrum for conidial (spore) production in the fungusStemphylium solaniWeber is presented. The response is in the far‐ultraviolet region (far u.v.). The spectrum shows a single peak at 280 nm, a shoulder at 260 nm, a trough at 250 nm, followed by a rise which is still rising at 230 nm, the shortest wavelength studied. The u.v. induced spore stimulation can be interrupted temporarily by irradiation in the visible region within 4 hr after induct

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06196.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The effects of u.v.‐irradiation at 254 nm upon lyophilized ribonuclease, lysozyme, insulin, and chymotrypsinogen have been investigated by electron spin resonance (ESR). enzymatic assay, and labeling of free radical sites with tritiated hydrogen sulfide (HST). The ESR signal of the irradiated protein diminishes on exposure to HST, and tritium becomes covalently bound to carbon. The distribution of tritium among the amino acids of each protein. studied as an indicator of the carbon free radical distribution, differs markedly from those observed previously to result from exposure to gamma radiation, electrical discharge. or hydrogen atoms. However, the earlier observation that the tritium distribution is influenced by protein conformation holds true as well for u.v.‐irradiation. Moreover, the distributions of tritium among the amino acids of u.v.‐irradiated proteins indicate a broad scattering of free radicals. Tyrosine and phenylalanine, residues that absorb light energy in the region of the wavelength employed, are not particularly important as radical carriers. Thus, for ribonuclease, these residues incorporated 3.8 and 1.5 per cent of the total tritium, but they absorb 51 and 12 per cent of the light, respectively. These results, together with the observed low recoveries of methionine, an amino acid that does not absorb at 254 nm, add weight to the concept that a migration of energy ensues after the initial absorption of light energy and that photolytic damage may thus be due to destruction of amino acids other than those initially absorbing the u.v.‐

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06197.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—π‐Electron calculations of the MO‐SCF‐CI type in the PPP approximations are carried out for the tetra pyrrole ring of the bacteriochlorophyll molecule, its mono cation and anion.According to the calculations the formation of the positive ion will be accompanied by the disappearance of the longest wavelength absorption band of the neutral system and the appearance of a new band near 1200 nm. Absorption changes of the same kind are found in the reaction center of photosynthetic bacteria upon illumination, supporting the hypothesis that the primary reaction is an expulsion of an electron from the π‐electron system of the reaction center bacterio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06198.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The influence of amino acid prestarvation on both the resistance to u.v. light and excision of thymine dimers of bacterial strains E. coli B/rhcr+thy‐trp‐, E. coli B/rhcr‐thy‐trp‐, and E,coli15 T‐555–7thy‐meth‐trp‐arg‐has been studied.The prestarvation increased the resistance of all the strains but reasonably inhibited excision of thymine dimers. Thus the enhancement of u.v. resistance after amino acid prestarvation was not due to more complete exc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06199.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—A detailed analysis of the effects of acidic pH values and of temperature on the ultraviolet absorption spectrum of papain demonstrated that the protein can exist in several more or less denatured conformations depending on the surrounding medium. Proflavine‐sensitized photooxidation of papain, under experimental conditions corresponding to the spectroscopically detected conformational states, allowed us to modify separately the five tryptophyl residues. Tryptophan‐7 and 69 appear to be at least partially exposed to the aqueous environment in native papain; however, the former becomes inaccessible to the photooxidizing agent at temperatures lower than 15°C. The photooxidative conversion of these residues to formyl‐kynurenine has no appreciable effect on the tertiary structure as well as on the enzymic activity of papain. On the other hand, tryptophan‐177. which appears to be largely buried, can also be modified with minor variations in the spatial geometry of the protein, but its indole moiety must be critically involved in the enzyme‐substrate interaction, since its conversion to formyl‐kynurenine almost completely inhibits the catalytic activity. Finally, tryptophan‐181 and ‐26 are deeply buried in internal hydrophobic clusters and become available to photooxidation only after the protein molecule has been extensively disorganized. Our results suggest that the solution conformation of some areas of the papain molecule may be different from that in the crystal state as deduced from X‐ray

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06200.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The photosensitized oxidation of I‐, tyrosine, and tryptophan by aqueous eosin has been investigated with a photostationary technique, in which the system is irradiated with sinusoidally modulated light and phase sensitive detection is used to measure the spectra of short‐lived intermediates and their rate constants. It has been shown that the principal oxidizing agent for I‐is semi‐oxidized eosin (X) produced by the reduction of oxygen by triplet state eosin. The same mechanism obtains when femcyanide ion is substitued for oxygen. A second oxidizing agent is effective in oxygenated solutions at high I‐concentrations, attributed to O2‐. TheXmechanism controls when tyrosine or tryptophan are irradiated at low substrate concentrations in the presence of oxygen or femcyanide. However, at high substrate concentrations, or in the absence of the electron accepting agents, the mechanism switches to the ‘dye‐substrate’ process where triplet state eosin oxidizes the aromatic substrate and is reduced to the semiquinone. The conversion quantum yields agree with the predictions based on the measured quenching and reac

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06201.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Irradiation of the carcinogenic benzo[a]pyrene(I) with 1‐methylcytosine hydro‐chloride(II) (molar ratio 1:10) at 3500 Å in methanol‐acetone produces the 6‐(1‐methylcytos‐5‐yl)‐benzo[a]pyrene(III). The structure of the product shows the hydrocarbon bound through the most active 6‐carbon atom to the nucleophilic 5‐position of the base. In the second part, the possibility of observing carcinogenic effects on the mouse skin from non‐carcinogenic hydrocarbons under the action of u.v. light is investigated. Both experiments provide evidence that the 4,5‐double bond (Kregion) of I presumably does not play a role in tri

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06202.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06203.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06204.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06205.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY