涉及光疗机制的生物光化学

本文对光生物和光化学的定义,反应机制的类型和光敏化作用等做了阐述。下面例举几个光疗的成果 1.光疗牛皮癣 经常使用的8-甲氧基补骨脂素在UVA的照射下,从基态被激发到三重态。它主要和DNA中的胸腺嘧啶,其次和色氨酸进行光环合加成,形成交联,阻止DNA和RNA的合成,抑制具过度增生 2.血卟啉衍生物(HPD)治癌 HPD有定位于癌组织的能力和光动力作用,可推断病人体内癌部位。 讨论了HPD的光疗机制,和酞菁相比,有各自的优缺点。 3.竹红菌素 主要治疗妇女外阴白色病变和疤痕疙瘩,抑制癌细胞生长。 讨论了竹红菌甲素和乙素及它们的氧化物的结构和活性。 在大于510nm的光照射下,也可抑制癌细胞的生长。列举了竹红菌素的优缺点。     

The impact of skin colour on human photobiological responses

Terrestrial solar ultraviolet radiation (UVR) exerts both beneficial and adverse effects on human skin. Epidemiological studies show a lower incidence of skin cancer in people with pigmented skins compared to fair skins. This is attributed to photoprotection by epidermal melanin, as is the poorer vitamin D status of those with darker skins. We summarize a wide range of photobiological responses across different skin colours including DNA damage and immunosuppression. Some studies show the generally modest photoprotective properties of melanin, but others show little or no effect. DNA photodamage initiates non‐melanoma skin cancer and is reduced by a factor of about 3 in pigmented skin compared with white skin. This suggests that if such a modest reduction in DNA damage can result in the significantly lower skin cancer incidence in black skin, the use of sunscreen protection might be extremely beneficial for susceptible population. Many contradictory results may be explained by protocol differences, including differences in UVR spectra and exposure protocols. We recommend that skin type comparisons be done with solar‐simulated radiation and standard erythema doses or physical doses (J/m²) rather than those based solely on clinical endpoints such as minimal erythema dose (MED).     

Cryptochromes: Photochemical and structural insight into magnetoreception

Cryptochromes (CRYs) function as blue light photoreceptors in diverse physiological processes in nearly all kingdoms of life. Over the past several decades, they have emerged as the most likely candidates for light‐dependent magnetoreception in animals, however, a long history of conflicts between in vitro photochemistry and in vivo behavioral data complicate validation of CRYs as a magnetosensor. In this review, we highlight the origins of conflicts regarding CRY photochemistry and signal transduction, and identify recent data that provides clarity on potential mechanisms of signal transduction in magnetoreception. The review primarily focuses on examining differences in photochemistry and signal transduction in plant and animal CRYs, and identifies potential modes of convergent evolution within these independent lineages that may identify conserved signaling pathways.     

Rapid Deamination of Cyclobutane Pyrimidine Dimer Photoproducts at TCG Sites in a Translationally and Rotationally Positioned Nucleosome in Vivo

Sunlight-induced C to T mutation hot spots in skin cancers occur primarily at methylated CpG sites that coincide with sites of UV-induced cyclobutane pyrimidine dimer (CPD) formation. The C and 5-methyl-C in CPDs are not stable and deaminate to U and T, respectively, which leads to the insertion of A by the DNA damage bypass polymerase η, thereby defining a probable mechanism for the origin of UV-induced C to T mutations. Deamination rates for T^mCG CPDs have been found to vary 12-fold with rotational position in a nucleosome in vitro. To determine the influence of nucleosome structure on deamination rates in vivo, we determined the deamination rates of CPDs at TCG sites in a stably positioned nucleosome within the FOS promoter in HeLa cells. A procedure for in vivo hydroxyl radical footprinting with Fe-EDTA was developed, and, together with results from a cytosine methylation protection assay, we determined the translational and rotational positions of the TCG sites. Consistent with the in vitro observations, deamination was slower for one CPD located at an intermediate rotational position compared with two other sites located at outside positions, and all were much faster than for CPDs at non-TCG sites. Photoproduct formation was also highly suppressed at one site, possibly due to its interaction with a histone tail. Thus, it was shown that CPDs of TCG sites deaminate the fastest in vivo and that nucleosomes can modulate both their formation and deamination, which could contribute to the UV mutation hot spots and cold spots.     

Geographic distribution of environmental factors influencing human skin coloration

Skin coloration in indigenous peoples is strongly related to levels of ultraviolet radiation (UVR). In this study, the relationships of skin reflectance to seasonal UVR levels and other environmental variables were investigated, with the aim of determining which variables contributed most significantly to skin reflectance. The UVR data recorded by satellite were combined with environmental variables and data on human skin reflectance in a geographic information system (GIS). These were then analyzed visually and statistically through exploratory data analysis, correlation analysis, principal components analysis, least-squares regression analysis, and nonlinear techniques. The main finding of this study was that the evolution of skin reflectance could be almost fully modeled as a linear effect of UVR in the autumn alone. This linear model needs only minor modification, by the introduction of terms for the maximum amount of UVR, and for summer precipitation and winter precipitation, to account for almost all the variation in skin reflectance. A further significant finding was that the effect of summer UVR seems to reach a threshold beyond which further adaptation is difficult.     

Light stimulation and darkness requirement for the symbiotic germination of Dactylorhiza majalis (Orchidaceae) in vitro

Germination percentage of Dactylorhiza majalis (Rchb.f.) Hunt & Summerh. (Orchidaceae) was increased by illuminating surface-sterilized, rinsed and incubated seeds with white light in 16 h photoperiods. Optimal exposures (10–14 days) raised germination from 40 to 75%. Longer light treatments resulted in reduced germination percentage and smaller seedlings. Only about 2% of the seeds could actually germinate in photoperiods; the germination of the rest was delayed by initial light and required about 14 days in constant darkness. Interruption of this darkness period with two consecutive photoperiods increased the germination percentage when the interruption occurred before day 8, but not when occurring later than that.     

Replaceability of Schiff base proton donors in light-driven proton pump rhodopsins

Many H⁺-pump rhodopsins conserve “H⁺ donor” residues in cytoplasmic (CP) half channels to quickly transport H⁺ from the CP medium to Schiff bases at the center of these proteins. For conventional H⁺ pumps, the donors are conserved as Asp or Glu but are replaced by Lys in the minority, such as Exiguobacterium sibiricum rhodopsin (ESR). In dark states, carboxyl donors are protonated, whereas the Lys donor is deprotonated. As a result, carboxyl donors first donate H⁺ to the Schiff bases and then capture the other H⁺ from the medium, whereas the Lys donor first captures H⁺ from the medium and then donates it to the Schiff base. Thus, carboxyl and Lys-type H⁺ pumps seem to have different mechanisms, which are probably optimized for their respective H⁺-transfer reactions. Here, we examined these differences via replacement of donor residues. For Asp-type deltarhodopsin (DR), the embedded Lys residue distorted the protein conformation and did not act as the H⁺ donor. In contrast, for Glu-type proteorhodopsin (PR) and ESR, the embedded residues functioned well as H⁺ donors. These differences were further examined by focusing on the activation volumes during the H⁺-transfer reactions. The results revealed essential differences between archaeal H⁺ pump (DR) and eubacterial H⁺ pumps PR and ESR. Archaeal DR requires significant hydration of the CP channel for the H⁺-transfer reactions; however, eubacterial PR and ESR require the swing-like motion of the donor residue rather than hydration. Given this common mechanism, donor residues might be replaceable between eubacterial PR and ESR.     

光生物学与光医学中的新技术及其应用

近几年内,光子生物学与光子医学发展非常快,本文主要从四个方面介绍了近期内在光子生物学与光子医学领城内取得的重要进展：(1)双光子技术,可检测胚胎活组织、确定生物的非损伤激发光阈值、对人体肌纤维进行三维成像;(2)光镊技术,用于研究细胞的应变能力、细胞膜的弹性、跟踪并描述单个分子之间的结合以及操纵DNA分子;(3)光学探针技术,检测疾病、研究构象变化;(4)光学成像技术,主要集中介绍对肌动蛋白的成像方面。