Action Spectrum Analysis of UVR Genotoxicity for Skin: The Border Wavelengths between UVA and UVB Can Bring Serious Mutation Loads to Skin

UVR causes erythema, which has been used as a standardized index to evaluate the risk of UVR for human skin.However, the genotoxic significance of erythema has not been elucidated clearly. Here, we characterized thewavelength dependence of the genotoxic and erythematic effects of UVR for the skin by analyzing the inductionkinetics of mutation and inflammation in mouse skin using lacZ-transgenic mice and monochromatic UVRsources. We determined their action spectra and found a close correlation between erythema and an epidermisspecific antigenotoxic response, mutation induction suppression (MIS), which suppressed the mutant frequencies (MFs) to a constant plateau level only 2–3-fold higher than the background MF at the cost of apoptotic cell death, suggesting that erythema may represent the threshold beyond which the antigenotoxic but tissuedestructive MIS response commences. However, we unexpectedly found that MIS attenuates remarkably at the border wavelengths between UVA and UVB around 315 nm, elevating the MF plateaus up to levels B40-foldhigher than the background level. Thus, these border wavelengths can bring heavier mutation loads to the skinthan the otherwise more mutagenic and erythematic shorter wavelengths, suggesting that erythema-based UVRrisk evaluation should be reconsidered

Nitrogen reduction by the Fe sites of synthetic [Mo₃S₄Fe] cubes

酵素を模倣した金属-硫黄化合物により窒素還元反応を実現 --持続可能社会に寄与するエネルギー変換に向けた第一歩--. 京都大学プレスリリース. 2022-07-07.SharedIt【https://rdcu.be/cQ644】で、出版社版（印刷・ダウンロード不可）の全文を閲覧することができます．A view-only version is available through the SharedIt link【https://rdcu.be/cQ644】Nitrogen (N₂) fixation by nature, which is a crucial process for the supply of bio-available forms of nitrogen, is performed by nitrogenase. This enzyme uses a unique transition-metal–sulfur–carbon cluster as its active-site co-factor ([(R-homocitrate)MoFe₇S₉C], FeMoco), and the sulfur-surrounded iron (Fe) atoms have been postulated to capture and reduce N₂ (refs.). Although there are a few examples of synthetic counterparts of the FeMoco, metal–sulfur cluster, which have shown binding of N₂ (refs.), the reduction of N₂ by any synthetic metal–sulfur cluster or by the extracted form of FeMoco has remained elusive, despite nearly 50 years of research. Here we show that the Fe atoms in our synthetic [Mo₃S₄Fe] cubes can capture a N₂ molecule and catalyse N₂ silylation to form N(SiMe₃)₃ under treatment with excess sodium and trimethylsilyl chloride. These results exemplify the catalytic silylation of N₂ by a synthetic metal–sulfur cluster and demonstrate the N₂-reduction capability of Fe atoms in a sulfur-rich environment, which is reminiscent of the ability of FeMoco to bind and activate N₂