Photochemistry and Photobiology

Cover image for Vol. 91 Issue 2

Edited By: Jean Cadet

Impact Factor: 2.684

ISI Journal Citation Reports © Ranking: 2013: 36/74 (Biophysics); 161/291 (Biochemistry & Molecular Biology)

Online ISSN: 1751-1097

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  • RESEARCH ARTICLE: Effects of Substituents on Synthetic Analogs of Chlorophylls. Part 4: How Formyl Group Location Dictates the Spectral Properties of Chlorophylls b, d and f

    RESEARCH ARTICLE: Effects of Substituents on Synthetic Analogs of Chlorophylls. Part 4: How Formyl Group Location Dictates the Spectral Properties of Chlorophylls b, d and f

    Photosynthetic organisms are adapted to light characteristics in their habitat in part via the spectral characteristics of the associated chlorophyll pigments, which differ in the position of a formyl group around the chlorin macrocycle (chlorophylls b, d, f) or no formyl group (chlorophyll a). To probe the origin of this spectral tuning, the photophysical and electronic structural properties of a new set of synthetic chlorins are reported. The zinc and free base chlorins have a formyl group at either the 2- or 3-position. The four compounds have fluorescence yields in the range 0.19–0.28 and singlet excited-state lifetimes of ca 4 ns for zinc chelates and ca 8 ns for the free base forms. The photophysical properties of the 2- and 3-formyl zinc chlorins are similar to those observed previously for 13-formyl or 3,13-diformyl chlorins, but differ markedly from those for 7-formyl analogs. Molecular-orbital characteristics obtained from density functional theory (DFT) calculations were used as input to spectral simulations employing the four-orbital model. The analysis has uncovered the key changes in electronic structure engendered by the presence/location of a formyl group at various macrocycle positions, which is relevant to understanding the distinct spectral properties of the natural chlorophylls a, b, d and f.

  • RESEARCH ARTICLE: Minimum Exposure Limits and Measured Relationships Between the Vitamin D, Erythema and International Commission on Non-Ionizing Radiation Protection Solar Ultraviolet

    RESEARCH ARTICLE: Minimum Exposure Limits and Measured Relationships Between the Vitamin D, Erythema and International Commission on Non-Ionizing Radiation Protection Solar Ultraviolet

    The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has established guidelines for exposure to ultraviolet radiation in outdoor occupational settings. Spectrally weighted ICNIRP ultraviolet exposures received by the skin or eye in an 8 h period are limited to 30 J m−2. In this study, the time required to reach the ICNIRP exposure limit was measured daily in 10 min intervals upon a horizontal plane at a subtropical Australian latitude over a full year and compared with the effective Vitamin D dose received to one-quarter of the available skin surface area for all six Fitzpatrick skin types. The comparison of measured solar ultraviolet exposures for the full range of sky conditions in the 2009 measurement period, including a major September continental dust event, show a clear relationship between the weighted ICNIRP and the effective vitamin D dose. Our results show that the horizontal plane ICNIRP ultraviolet exposure may be used under these conditions to provide minimum guidelines for the healthy moderation of vitamin D, scalable to each of the six Fitzpatrick skin types.

  • SPECIAL ISSUE RESEARCH ARTICLE: Regulation and Disregulation of Mammalian Nucleotide Excision Repair: A Pathway to Nongermline Breast Carcinogenesis

    SPECIAL ISSUE RESEARCH ARTICLE: Regulation and Disregulation of Mammalian Nucleotide Excision Repair: A Pathway to Nongermline Breast Carcinogenesis

    Nucleotide excision repair (NER) is an important modulator of disease, especially in constitutive deficiencies such as the cancer predisposition syndrome Xeroderma pigmentosum. We have found profound variation in NER capacity among normal individuals, between cell-types and during carcinogenesis. NER is a repair system for many types of DNA damage, and therefore many types of genotoxic carcinogenic exposures, including ultraviolet light, products of organic combustion, metals and oxidative stress. Because NER is intimately related to cellular metabolism, requiring components of both the DNA replicative and transcription machinery, it has a narrow range of functional viability. Thus, genes in the NER pathway are expressed at the low levels manifested by, for example, nuclear transcription factors. As NER activity and gene expression vary by cell-type, it is inherently epigenetically regulated. Furthermore, this epigenetic modulation is disregulated during sporadic breast carcinogenesis. Loss of NER is one basis of genomic instability, a required element in cellular transformation, and one that potentially influences response to therapy. In this study, we demonstrate differences in NER capacity in eight adult mouse tissues, and place this result into the context of our previous work on mouse extraembryonic tissues, normal human tissues and sporadic early stage human breast cancer.

  • INVITED REVIEW: UV Signature Mutations

    INVITED REVIEW: UV Signature Mutations

    Sequencing complete tumor genomes and exomes has sparked the cancer field's interest in mutation signatures for identifying the tumor's carcinogen. This review and meta-analysis discusses signatures and their proper use. We first distinguish between a mutagen's canonical mutations—deviations from a random distribution of base changes to create a pattern typical of that mutagen—and the subset of signature mutations, which are unique to that mutagen and permit inference backward from mutations to mutagen. To verify UV signature mutations, we assembled literature datasets on cells exposed to UVC, UVB, UVA, or solar simulator light (SSL) and tested canonical UV mutation features as criteria for clustering datasets. A confirmed UV signature was: ≥60% of mutations are CT at a dipyrimidine site, with ≥5% CCTT. Other canonical features such as a bias for mutations on the nontranscribed strand or at the 3′ pyrimidine had limited application. The most robust classifier combined these features with criteria for the rarity of non-UV canonical mutations. In addition, several signatures proposed for specific UV wavelengths were limited to specific genes or species; UV's nonsignature mutations may cause melanoma BRAF mutations; and the mutagen for sunlight-related skin neoplasms may vary between continents.

  • INVITED REVIEW: Oculocutaneous Albinism in Sub-Saharan Africa: Adverse Sun-Associated Health Effects and Photoprotection

    INVITED REVIEW: Oculocutaneous Albinism in Sub-Saharan Africa: Adverse Sun-Associated Health Effects and Photoprotection

    Oculocutaneous albinism (OCA) is a genetically inherited autosomal recessive condition. Individuals with OCA lack melanin and therefore are susceptible to the harmful effects of solar ultraviolet radiation, including extreme sun sensitivity, photophobia and skin cancer. OCA is a grave public health issue in sub-Saharan Africa with a prevalence as high as 1 in 1000 in some tribes. This article considers the characteristics and prevalence of OCA in sub-Saharan African countries. Sun-induced adverse health effects in the skin and eyes of OCA individuals are reviewed. Sun exposure behavior and the use of photoprotection for the skin and eyes are discussed to highlight the major challenges experienced by these at-risk individuals and how these might be best resolved.

  • RESEARCH ARTICLE: Effects of Substituents on Synthetic Analogs of Chlorophylls. Part 4: How Formyl Group Location Dictates the Spectral Properties of Chlorophylls b, d and f
  • RESEARCH ARTICLE: Minimum Exposure Limits and Measured Relationships Between the Vitamin D, Erythema and International Commission on Non-Ionizing Radiation Protection Solar Ultraviolet
  • SPECIAL ISSUE RESEARCH ARTICLE: Regulation and Disregulation of Mammalian Nucleotide Excision Repair: A Pathway to Nongermline Breast Carcinogenesis
  • INVITED REVIEW: UV Signature Mutations
  • INVITED REVIEW: Oculocutaneous Albinism in Sub-Saharan Africa: Adverse Sun-Associated Health Effects and Photoprotection

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UVB radiation causes formation of specific DNA damage photoproducts between adjacent pyrimidine bases. These DNA photoproducts are repaired by a process called nucleotide excision repair. When left unrepaired, UVB-induced DNA damage leads to accumulation of mutations, predisposing affected individuals to carcinogenesis as well as to premature aging. Regulation of nucleotide excision repair is an attractive avenue to preventing or reversing these detrimental consequences of impaired nucleotide excision repair. Recent studies on molecular mechanisms regulating nucleotide excision repair by extracellular cues and intracellular signaling pathways, with a special focus on the molecular regulation of individual repair factors are reviewed by Palak Shah and Yu-Ying He in the paper “Molecular Regulation of UV-Induced DNA Repair“ on pages 254 – 264 in this issue.
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