Photochemistry and Photobiology 

About: Photochemistry and Photobiology is an academic journal published by Wiley-Blackwell. The journal publishes majorly in the area(s): Singlet oxygen & Excited state. It has an ISSN identifier of 0031-8655. Over the lifetime, 11917 publications have been published receiving 413026 citations.

How does photodynamic therapy work

Abstract: Those readers already familiar with the field of photodynamic therapy (PDT)t will consider this title somewhat presumptuous since it implies that the answer to the posed question is known. Indeed, answers to many questions regarding PDT have been found over the past decade, but a comprehensive understanding of all mechanisms involved in PDT tumor destruction has not yet emerged. This paper will attempt to deal with this complex subject by giving a sequential account of the effects occurring during PDT tissue treatment on a cellular and tissue level. Photodynamic therapy is based on the dye-sensitized photooxidation of biological matter in the target tissue (Foote, 1990). This requires the presence of a dye (sensitizer) in the tissue to be treated. Although such sensitizers can be naturally occurring constituents of cells and tissues, in the case of PDT they are introduced into the organism as the first step of treatment. In the second step, the tissuelocalized sensitizer is exposed to light of wavelength appropriate for absorption by the sensitizer. Through various photophysical pathways, also involving molecular oxygen, oxygenated products harmful to cell function arise and eventual tissue destruction results. In keeping with the chronological nature of this review, the subject matter will be divided into the

Cooperation of charges in photosynthetic o2 evolution–i. a linear four step mechanism

Abstract: — Using isolated chloroplasts and techniques as described by Joliot and Joliot[6] we studied the evolution of O2 in weak light and light flashes to analyze the interactions between light induced O2 precursors and their decay in darkness. The following observations and conclusions are reported: 1. Light flashes always produce the same number of oxidizing equivalents either as precursor or as O2. 2. The number of unstable precursor equivalents present during steady state photosynthesis is ∼ 1.2 per photochemical trapping center. 3. The cooperation of the four photochemically formed oxidizing equivalents occurs essentially in the individual reaction centers and the final O2 evolution step is a one quantum process. 4. The data are compatible with a linear four step mechanism in which a trapping center, or an associated catalyst, (S) successively accumulates four + charges. The S4+ state produces O2 and returns to the ground state S0. 5. Besides S0 also the first oxidized state S+ is stable in the dark, the two higher states, S2+ and S3+ are not. 6. The relaxation times of some of the photooxidation steps were estimated. The fastest reaction, presumably S*1←S2, has a (first) half time ≤ 200 μsec. The S*2 state and probably also the S*0 state are processed somewhat more slowly (˜ 300–400 μsec).

Green fluorescent protein

Abstract: This invention provides a cell comprising a DNA molecule having a regulatory element from a gene, other than a gene encoding a green fluorescent protein operatively linked to a DNA sequence encoding the green fluorescent protein. This invention also provides living organisms which comprise the above-described cell. This invention also provides a method for selecting cells expressing a protein of interest which comprises: a) introducing into the cells a DNAI molecule having DNA sequence encoding the protein of interest and DNAII molecule having DNA sequence encoding a green fluorescent protein; b) culturing the introduced cells under conditions permitting expression of the green fluorescent protein and the protein of interest; and c) selecting the cultured cells which express green fluorescent protein, thereby selecting cells expressing the protein of interest. Finally, this invention provides various uses of a green fluorescent protein.

Environmental Significance of Anthocyanins in Plant Stress Responses

Abstract: — Anthocyanins are water-soluble pigments found in all plant tissues throughout the plant kingdom. Our understanding of anthocyanin biosynthesis and its molecular control has greatly improved in the last decade. The adaptive advantages of anthocyanins, especially in non-reproductive tissues, is much less clear. Anthocyanins often appear transiently at specific developmental stages and may be induced by a number of environmental factors including visible and UVB radiation, cold temperatures and water stress. The subsequent production and localization of anthocyanins in root, stem and especially leaf tissues may allow the plant to develop resistance to a number of environmental stresses. This article reviews the environmental induction of anthocyanins and their proposed importance in ameliorating environmental stresses induced by visible and UVB radiation, drought and cold temperatures.

The Protective Role of Melanin Against UV Damage in Human Skin

Abstract: Human skin is repeatedly exposed to UVR that influences the function and survival of many cell types and is regarded as the main causative factor in the induction of skin cancer. It has been traditionally believed that skin pigmentation is the most important photoprotective factor, as melanin, besides functioning as a broadband UV absorbent, has antioxidant and radical scavenging properties. Besides, many epidemiological studies have shown a lower incidence for skin cancer in individuals with darker skin compared to those with fair skin. Skin pigmentation is of great cultural and cosmetic importance, yet the role of melanin in photoprotection is still controversial. This article outlines the major acute and chronic effects of UVR on human skin, the properties of melanin, the regulation of pigmentation and its effect on skin cancer prevention.