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51.
《Magnetic resonance in chemistry : MRC》2003,41(6):466-474
This paper presents the high‐resolution 13C and 15N cross‐polarization magic angle spinning (CP/MAS) NMR spectra of three natural melanin solids: Sepia officinalis melanin, Sepia officinalis melanin free acid (MFA) and Human hair melanin. The functional group characterization of Human hair melanin by NMR is the first to date and the 13C CP/MAS NMR spectra reported here show improved resolution of chemically inequivalent sites. The observed spectral regions of the solid melanin samples can be assigned to the postulated structural unit of the polymer chain of Sepia MFA derived from solution‐state NMR studies. To assist in the assignment of functional groups in the spectra, the solid‐state CP/MAS NMR spectra are compared with high‐resolution 13C and 15N CP/MAS spectra of four model compounds, L ‐dopa, dopamine, 2‐methoxycarbonyl‐3‐ethoxycarbonyl‐4‐methylpyrrole and ethyl 5,6‐dimethoxyindole‐2‐carboxylate. To aid further in the assignment of protonated and non‐protonated carbon atoms, CP contact time dependence and non‐quaternary carbon suppression (NQS) experiments were performed on the melanin samples. The 15N CP/MAS spectra of the melanin samples confirm the presence of indole and pyrrole units in the melanin polymer chain. The NMR peaks observed in all of the melanin samples are relatively broad, presumably owing to the presence of free radicals. Electron spin resonance (ESR) data shows that all three melanin samples contain localized free radicals (g = 2.007), with the Sepia melanin containing a 10‐fold higher free radical density than Human hair melanin. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
52.
产黑色素B.thuringiensis重组菌株的构建及其培养条件的优化 总被引:9,自引:0,他引:9
将嗜麦芽假单胞菌中产生黑色素的基因(mel gene)克隆到穿梭载体pHT3101中,并将它处于表达系统cry3A的控制下,构建得到重组质粒pHTAM.将此重组质粒用电脉冲的方法转入苏云金芽胞杆菌受体菌株BMB171中,得到重组菌株RSA.研究结果表明,处于cry3A控制下nel基因在BMBl71菌株中得到了成功的表达.本研究进一步采用红外光谱扫描法检测RSA所产黑色素的性质,并通过改变培养条件来提高黑色素的产量. 相似文献
53.
54.
《Macromolecular bioscience》2017,17(5)
Melanin is an effective absorber of light and can extend to near infrared (NIR) regions. In this study, a natural melanin is presented as a photothermal therapeutic agent (PTA) because it provides a good photothermal conversion efficiency, shows biodegradability, and does not induce long‐term toxicity during retention in vivo. Poloxamer solution containing melanin (Pol–Mel) does not show any precipitation and shows sol–gel transition at body temperature. After irradiation from 808 nm NIR laser at 1.5 W cm−2 for 3 min, the photothermal conversion efficiency of Pol–Mel is enough to kill cancer cells in vitro and in vivo. The tumor growth of mice bearing CT26 tumors treated with Pol–Mel injection and laser irradiation is suppressed completely without recurrence postirradiation. All these results indicate that Pol–Mel can become an attractive PTA for photothermal cancer therapy.
55.
合成了五种多金属氧酸盐. 以B16小鼠黑色素瘤细胞为模型, 用噻唑蓝(MTT)法检测细胞存活率, 酶标法测定抗氧化活性和内黑色素含量及酪氨酸酶活性, 最后用分子对接模拟多金属氧酸盐和酪氨酸酶结合的机制. 研究结果表明, 两种磷钼酸(H7[P2Mo17VO62]和H8[P2Mo16V2O62])是高效的黑色素生成抑制剂, 在200 μmol/L的浓度下对黑色素合成的抑制率为74.40%和75.14%, 对细胞内酪氨酸酶活性的抑制率为35.71%和40.00%, 随着钒原子取代个数的增加, 两种抑制活性均逐渐降低. H7[P2Mo17VO62]和H8[P2Mo16V2O62]对细胞没有毒性. 两种多酸都有较好的1,1-二苯基-2-三硝基苯肼(DPPH)清除能力, IC50分别为1.683和2.800 mg/mL. 分子对接分数低于–146 kJ/mol. 综上所述, H7[P2Mo17VO62]和H8[P2Mo16V2O62]能抑制B16细胞黑色素的生成, 其机制与抑制酪氨酸酶的活性有关. 相似文献
56.
Masahiro Yamasaki Shinya Hasegawa Hiroshi Takahashi Yuka Kobayashi Chihiro Sakai Yoko Ashizawa 《Natural product research》2015,29(22):2103-2106
One of the activities of placental extracts (PEs) is skin-whitening effect, but the physiological and genetic mechanism for this effect has not yet been clarified. Here, we focus on PE as a regulator of antioxidant enzyme genes. Porcine PE was prepared, and its activity was investigated in B16 melanoma cells. PE treatment decreased the melanin content of UV-irradiated B16 cells in a dose-dependent manner. PE directly reduced the enzyme activity of tyrosinase in a cell-free assay. In addition, PE treatment increased the gene expression of cytosolic superoxide dismutase (SOD-1), extracellular SOD (SOD-3) and catalase but did not affect the expression of tyrosinase. Moreover, PE protected the B16 cells from H2O2-induced cell death. Taken together, our data suggest that PEs could play a role not only as a suppressor of melanin synthesis but also as a regulator of antioxidant genes and might protect the skin against oxidative stress. 相似文献
57.
Pathomthat Srisuk Vitor M. Correlo Isabel B. Leonor 《Journal of Macromolecular Science: Physics》2015,54(12):1532-1540
Melanins are phenol-based pigments with the potential for widespread applications, including bioelectronics and tissue engineering. The concentration-dependent structural transition of sepia melanin in water is analyzed. This biopolymer at high concentration gives the well-known nanospheres, whereas sample dilution gives unforeseen nanofibres exhibiting the structural features of mature amyloid fibrils. We propose a mechanism of pigment self-assembly dependent on the interaction of residual melanosomal protein(s) with eumelanin heteropolymer. Our results contribute to understanding the peculiar physicochemical properties of this ubiquitous pigment. 相似文献
58.
59.
V. A. Lapina P. P. Pershukevich A. E. Dontsov M. V. Bel’kov 《Journal of Applied Spectroscopy》2008,75(1):53-63
The spectra and kinetics of fluorescence of two-component solutions of the chlortetracycline (CHTC)-DOPA-melanin (melanin
or ME) system in water have been investigated. The data obtained have been compared to similar data for solutions of CHTC-melanosome
from bull eye (MB), which contains natural melanin, in K-phosphate buffer at pH 7.4. The overall results indicate the occurrence
of complexation between molecules of CHTC and ME as they are being excited. The studies of complexation in the solution of
CHTC-MB in the buffer are complicated by the formation of a CHTC-buffer complex. The effect of optical radiation in the range
330–750 nm on the CHTC-ME complex shows selectivity: the greatest change in the spectrum occurs when the wavelength of the
exciting radiation coincides with the long-wavelength band maximum of the fluorescence excitation spectrum of the CHTC-ME
complex in aqueous solution. In this range, CHTC and especially ME show high photochemical stability. The nature of the radiation
effect on the studied compounds in the hard UV range (λ < 330 nm) differs greatly from that in the range 330–750 nm. It is
apparently accompanied by significant photochemical transmutations of all system components. By comparing the characteristics
of the CHTC-ME systems with those of the related drug doxycycline (DC-ME), the conclusion has been made that the chlorine
atom plays a vital role in formation of the short-wavelength band in the fluorescence spectrum of the CHTC-ME complex.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 52–62, January–February, 2008. 相似文献
60.
Thiopronine (N-2-mercaptopropionyl-glycine, NMPG) inhibits the o-dihydroxy-phenolase activities of mushroom tyrosinase. When d,l-3-4-dihydroxyphenylalanine (DOPA) is employed as substrate, the inhibition was found to be a competitive-type with K(i) of 0.95 micro m. We found in addition that thiopronine interacts with the enzymatic generated product (o-quinone) to form a colourless conjugate compound causing an apparent inhibition. These data suggest that thiopronine inhibits mushroom tyrosinase activity in two ways: (1) by forming an adduct with dopaquinone; and (2) by direct interaction with the enzyme probably towards the copper (II) present in the active site or cysteine-rich domains. This finding was indicated by the presence of a lag period prior to the attainment of an inhibited steady-state rate. Both lag period and steady-state rate were dependent on thiopronine and substrate concentrations. An increase of thiopronine concentration causes longer lag periods as well as a concomitant decrease in the tyrosinase activity. The presence of an excess of copper (II) reverses the inhibition exerted by thiopronine. 相似文献