Recent advances in urocanic acid photochemistry, photobiology and photoimmunology.

Urocanic acid (UCA), produced in the upper layers of mammalian skin, is a major absorber of ultraviolet radiation (UVR). Originally thought to be a 'natural sunscreen', studies conducted a quarter of a century ago proposed that UCA may be a chromophore for the immunosuppression that follows exposure to UVR. With its intriguing photochemistry, its role in immunosuppression and skin cancer development, and skin barrier function, UCA continues to be the subject of intense research effort. This review summarises the photochemical, photobiological and photoimmunological findings regarding UCA, published since 1998.     

(Re)Greening photochemistry: using light for degrading persistent organic pollutants

Light is a cheap and abundant chemical reagent, capable of inducing highly selective reactions, some of which cannot be reasonably carried out by alternative ways nowadays. Photochemical processes may take place directly from the excited states or short-lived intermediates generated after light absorption or, alternatively, through reaction with species indirectly generated by the action of light on other chemicals present in the medium (catalysts or secondary reagents). As a consequence a range of possibilities are open to transform and/or degrade refractory pollutants or undesired chemicals or microbia in air, water, soil, on surfaces, etc., as well as other applications described below.     

The digital photobiology compendium: perspectives on a web-based teaching tool from learners and developers.

The DPC offers many benefits for learners, teachers and developers involved in creation of teaching materials in photobiology. Modifications and additions can be made relatively easily. Anonymous peer review of modules, allowing them to be cited as peer reviewed publications, is likely to encourage new submissions.     

Circadian variability in the photobiology of Phaeodactylum tricornutum: pigment content

Circadian variations of pigment content in the diatom Phaeodactylumtricornutum were analyzed in different light regimes. The studywas aimed at discerning the role of putative endogenous controlsfrom the constraint imposed by the alternation of light (L)and dark (D) periods. Our experiments showed that in a typicalLD cycle of illumination, pigment synthesis follows the somaticgrowth of the cell, both arresting during D periods. In particular,the diurnal increase of chlorophyll a content was proportionalto the increase in cell size and preceding cell division, occurringat night. By contrast, diadinoxanthin and ß–carotene displayed different phases, which is likely to be relatedto their involvement in photoprotection mechanisms. The experimentsalso showed that the synthesis of both photosynthetic and photoprotectivepigments was dependent not only on light availability and thephasing of somatic growth, but also responded to other internalregulation. Over the time scale of the experiments (hours todays), the removal of LD–DL triggers impaired cell physiology,whereas the circadian patterns in pigment synthesis persisted.Our results support the hypothesis that an internal regulationof cell biosynthetic machinery can improve phytoplankton fitness,even in high variable environments such as the oceanic mixedlayers. Therefore, we suggest that phytoplankton growth dependsnot only on the availability of external resources, but alsoon internal regulatory mechanisms whose unveiling would furtherour understanding of phytoplankton diversity and dynamics.     

Bacteriorhodopsin: photochemistry and energy conversion

This study examined effects of fatty acids on the metabolism of 1,3 diphenylisobenzofuran (DPBF) and benzo(α) pyrene (BP) by rat or human colonic mucosal microsomes. Arachidonate, linoleate (25 μM) or their hydroperoxides increased oxidation of DPBF or BP 4 to 5-fold, whereas saturated fatty acids and NADPH had no effect. Studies of the influence of O₂ exclusion and indomethacin on DPBF and BP oxidation were consistent with the existence of both cyclooxygenase dependent and independent pathways for fatty acid stimulation of colonic microsomal drug oxidation. These results may have a bearing on the increased prevalence of colon cancer in populations with high fat intakes.     

Naturally occurring organic osmolytes: from cell physiology to disease prevention

Osmolytes are naturally occurring organic compounds, which represent different chemical classes including amino acids, methylamines, and polyols. By accumulating high concentrations of osmolytes, organisms adapt to perturbations that can cause structural changes in their cellular proteins. Osmolytes shift equilibrium toward natively-folded conformations by raising the free energy of the unfolded state. As osmolytes predominantly affect the protein backbone, the balance between osmolyte-backbone interactions and amino acid side chain-solvent interactions determines protein folding. Abnormal cell volume regulation significantly contributes to the pathophysiology of several disorders, and cells respond to these changes by importing, exporting, or synthesizing osmolytes to maintain volume homeostasis. In recent years, it has become quite evident that cells regulate many biological processes such as protein folding, protein disaggregation, and protein-protein interactions via accumulation of specific osmolytes. Many genetic diseases are attributed to the problems associated with protein misfolding/aggregation, and it has been shown that certain osmolytes can protect these proteins from misfolding. Thus, osmolytes can be utilized as therapeutic targets for such diseases. In this review article, we discuss the role of naturally occurring osmolytes in protein stability, underlying mechanisms, and their potential use as therapeutic molecules.     

Primary photochemistry of reaction centers from the photosynthetic purple bacteria

Photosynthetic organisms transform the energy of sunlight into chemical potential in a specialized membrane-bound pigment-protein complex called the reaction center. Following light activation, the reaction center produces a charge-separated state consisting of an oxidized electron donor molecule and a reduced electron acceptor molecule. This primary photochemical process, which occurs via a series of rapid electron transfer steps, is complete within a nanosecond of photon absorption. Recent structural data on reaction centers of photosynthetic bacteria, combined with results from a large variety of photochemical measurements have expanded our understanding of how efficient charge separation occurs in the reaction center, and have changed many of the outstanding questions.Abbreviations BChl bacteriochlorophyll - P a dimer of BChl molecules - BPh bacteriopheophytin - Q_A and Q_B quinone molecules - L, M and H light, medium and heavy polypeptides of the reaction center     

Preface: to the special issue: photochemistry and electrochemistry of natural and artificial photosynthesis

Photosynthesis Research -     

Photosynthetic antenna proteins: 100 ps before photochemistry starts

All photosynthetic organisms require a light harvesting system to funnel excitation energy towards the photosynthetic reaction centre, a process which can take 100 ps. Laser spectroscopy allows us to measure rates of energy transfer between pigments of the light harvesting system for the first time. These rates are correlated with models of the light harvesting apparatus.     

Imitational modeling of evolution: from organic macromolecules to protocell and animal cell

A dynamic imitational model is developed of initial stages of cell evolution based on role of environmental cation concentration. The model is developed on our hypothesis, concerning the medium of the appearance of protocells. Could be potassium water reservoirs rather than sea salt water with its predominance of sodium salts. The necessary elements of appearance the protocells served organic molecules, code of their synthesis, and formation of macromolecules under favorable ion concentration in environment High K+ and Mg2+ concentration and bow Na+. The model is based on an assumption that one of the first stages in evolution of life was the appearance in potassium-magnesium water reservoirs of organic molecules capable for selfreplication on the basis of genetic code and formation of protocells with potassium cytoplasm. The model has demonstrated necessity of formation of cell envelope for development of the protocell. Replacement of the dominant cation in water reservoirs-potassium by sodium-required the appearance of ion-transporting devices in plasma membrane and their participation in adaptation of cells to environment. This stage of evolution was accompanied by the most important morpho-functional event--formation of the plasma membrane instead of cell envelope. The membrane provided the ion asymmetry in the cell (preservation of K+ in it) relatively to the sodium external medium for maintaining optimal intracellular medium. In the model system, predecessors of animal cells elaborated mechanism of maintenance of the potassium cytoplasm with the sodium counter-ion dominating in the environment.     

Properties and photochemistry of a halorhodopsin from the haloalkalophile, Natronobacterium pharaonis

Pharaonis halorhodopsin is a light-driven transport system for chloride, similarly to the previously described halorhodopsin, but we find that it transports nitrate as effectively as chloride. We studied the photoreactions of the purified, detergent-solubilized pharaonis pigment with a gated multichannel analyzer. At a physiological salt concentration (4 M NaCl), the absorption spectra and rate constants of rise and decay for intermediates of the photocycle were similar to those for halorhodopsin. In buffer containing nitrate, halorhodopsin exhibits a second, truncated photocycle; this difference in the photoreaction of the pigment occurs when an anion is bound in such a way as to preclude transport. As expected from the lack of anion specificity in the transport, the photocycle of pharaonis halorhodopsin was nearly unaffected by replacement of chloride with nitrate. All presumed buried positively charged residues, which might play a role in anion binding, are conserved in the two pigments. At the extracellular end of the presumed helix C, however, an arginine residue is found in halorhodopsin, but not in pharaonis halorhodopsin, and an arginine-rich segment between the presumed helices A and B in halorhodopsin is replaced by a less positively charged sequence in pharaonis halorhodopsin (Lanyi, J. K., Duschl, A., Hatfield, G. W., May, K., and Oesterhelt, D. (1990) J. Biol. Chem. 265, 1253-1260). One or both of these alterations may explain the difference in the anion selectivity of the two proteins.     

Solid-phase extraction procedure to remove organic acids from honey

A solid-phase extraction procedure was applied to remove organic acids from honey. Malic, maleic, citric, succinic and fumaric acids were isolated with an anion-exchange cartridge. The different parameters which affected the extraction procedure were studied and optimised to establish the optimal conditions for maximum recovery of organic acids and minimum extraction of interferences. The optimised procedure used a cartridge which was activated with 10 ml of 0.1 M sodium hydroxide solution (percolation rate 3 ml/min). A 10 ml volume of honey solution was passed at a flow-rate of 0.5 ml/min. The cartridge was washed with 10 ml of water (3 ml/min) and organic acids were eluted with 4 ml of 0.1 M sulfuric acid (0.5 ml/min). This solution was injected directly into the chromatograph. When this procedure was carried out on standard solutions of organic acids, recoveries between 99.2 and 103.4% were found. If this procedure was applied to honey samples these recoveries were also satisfactory and ranged from 62.9 to 99.4%.     

系统生物学--从生物分子到机体反应过程

目　　录一、后基因组时代二、老生常谈的问题———定量问题三、模型与模拟四、从何着手五、结论2 0 0 3年 9月 15日 ,美国国立卫生研究院 (NIH)的官方网站上发布了这样一组消息和相关评论(Changingthefaceofbiology :NIGMSfundscentersofexcellenceatHarvardandMITseekingtou