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1.
Hisao Tsukamoto Yoshihiro Kubo David L. Farrens Mitsumasa Koyanagi Akihisa Terakita Yuji Furutani 《The Journal of biological chemistry》2015,290(45):27176-27187
Melanopsins play a key role in non-visual photoreception in mammals. Their close phylogenetic relationship to the photopigments in invertebrate visual cells suggests they have evolved to acquire molecular characteristics that are more suited for their non-visual functions. Here we set out to identify such characteristics by comparing the molecular properties of mammalian melanopsin to those of invertebrate melanopsin and visual pigment. Our data show that the Schiff base linking the chromophore retinal to the protein is more susceptive to spontaneous cleavage in mammalian melanopsins. We also find this stability is highly diversified between mammalian species, being particularly unstable for human melanopsin. Through mutagenesis analyses, we find that this diversified stability is mainly due to parallel amino acid substitutions in extracellular regions. We propose that the different stability of the retinal attachment in melanopsins may contribute to functional tuning of non-visual photoreception in mammals. 相似文献
2.
Isolation of steroidal glycoalkaloids from Solanum incanum by two countercurrent chromatographic methods. 总被引:1,自引:0,他引:1
Using a bioassay for inhibition of plant growth and a combination of two countercurrent chromatographies: rotation locular countercurrent chromatography and droplet countercurrent chromatography, two biologically active glycosidal alkaloids, solasonine and solamargine were isolated from fresh ripe fruit of Solanum incanum. The combination of these chromatographic techniques has established an efficient isolation of polar phytochemicals of steroidal glycoalkaloids. 相似文献
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Pellicles were isolated from Paramecium caudatum for a study of the properties of its insoluble ATPase [EC 3.6.1.3] activity. Pellicular ATPase was solubilized by sonication and fractionated by sucrose density gradient centrifugation. The sedimentation coefficient of the ATPase was about 9S. The ATPase required Ca2+ for maximum activation. Addition of neutral salts to the assay medium inhibited the activity. Substrate specificity for ATP was low; other nucleoside triphosphates were hydrolyzed at about the same rate as ATP; AMP, pyrophosphate, and p-nitrophenyl phosphate were not hydrolyzed. The ATPase activity of the pellicle preparation had a pH optimum at pH 6.5, and a Michaelis constant of 9 micrometer. On the other hand, the enzymatic properties of the ATPase were somewhat modified by the procedure of solubilization and fractionation. The pellicular ATPase does not resemble ciliary dynein ATPase or the soluble ATPase of Tetrahymena. 相似文献
5.
Hiroyoshi Kubo 《Mycoscience》2012,53(2):147-151
Pilobolus crystallinus has three putative glyceraldehyde-3-phosphate dehydrogenase (gapdh) genes (pcgapdh1, pcgapdh2 and pcgapdh3). The results of this study demonstrate that expression of pcgapdh2 was increased by irradiation and that this increased expression was correlated with the formation of asexual reproductive
organs (trophocysts). Interestingly, expression of pcgapdh2 was restricted to trophocysts. The formation of trophocysts was likely promoted by light, and the expression of pcgapdh2 was increased as a result of trophocyst formation. This is the first report that shows the regulation of a gapdh gene in an organ-specific manner in fungi. 相似文献
6.
Involvement of the Binuclear Copper Site in the Proteolytic Activity of Polyphenol Oxidase 总被引:2,自引:0,他引:2
Plant polyphenol oxidase (PPO) is apt to degrade during andeven after purification. We developed a method to stabilizePPO by 0.3 M NaCl, 0.1% (w/v) Tween 20, and 50% (w/v) ethyleneglycol at pH 6.5. The protein slowly degraded by itself whenthe stabilizing reagents were removed. Ascorbate and/or H2O2accelerated the degradation. The ascorbate-induced degradationwas inhibited by catalase, suggesting that H2O2 is generatedthrough reduction of PPO by ascorbate. It is likely that dissolvedoxygen is converted to peroxide through two-electron reductionby the reaction center of PPO, binuclear Cu site, and a Fenton-typereaction occurred on it. This understanding was supported bythe finding that the H2O2-induced degradation was inhibitedby metal-chelators as well as by polyphenolic substrate of PPO.Considering the postulated mechanism of the self-degradationof PPO, we re-examined the degradation of the 23-kDa proteinof PSII by PPO [Kuwabara et al. (1997) Plant Cell Physiol. 38:179]. The obtained results suggested that the 23-kDa proteintriggers the active oxygen production by the binuclear Cu site,probably as reductant, and receives the radical species preferentiallyto the polypeptide moiety of PPO. (Received April 15, 1999; Accepted July 21, 1999) 相似文献
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Tomohiko J. Itoh Hidemi Sato 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,800(1):21-27
The initial rate and final extent of polymerization of both bovine brain tubulin and sea urchin egg tubulin were enhanced in the presence of 2H2O. The yields were increased in association with the elevation of the 2H2O concentration. 2H2O also reduced the critical concentration for polymerization of brain tubulin. Thermodynamic analysis was attempted using the temperature dependence of the critical concentration for polymerization in the presence of 2H2O. We obtained linear van 't Hoff plots and calculated thermodynamic parameters which were positive and were increased with the elevation of the 2H2O concentration. The enhancement of the polymerization of tubulin by 2H2O could, therefore, be the result of the strenghening of intra-and/or inter-molecular hydrophobic interactions of the tubulin molecules. We believe that the increase in lenghth and number of microtubules of the mitotic spindles in the dividing cells of the eukaryotes with 2H2O may be caused by the direct involvement of 2H2O in the polymerization of tubulin. 相似文献
10.
A striking difference in radiosensitivity was noted between C3H/He (H-2k) and C57BL/6J (H-2b) strain mice when assessed by primary anti-SRBC PFC response of intact animals and primary cell-mediated lympholysis (CML) response of spleen cells to allogeneic cells in vitro, the C3H strain being more radioresistant. On the other hand, when C3H and B6 mice were exposed to 6.62 to 10.40 grays (Gy) of x-rays and then were transplanted with 2 X 10(6) bone marrow cells from B6C3F1 (H-2b/k) donor mice within 3 hr or at 24 hr after radiation exposure, the early mortality caused by residual host-vs-graft (HVG) reaction was much higher when C3H mice were used as recipients. Furthermore, the proportion of surviving animals manifesting host-type lymphohemopoiesis, i.e., host-type revertants, was much higher in B6C3F1 to C3H than in B6C3F1 to B6 combination. Spleen cells from such host-type revertants manifested strong anti-donor reactivity when assessed by mixed lymphocyte reaction (MLR) and/or CML in vitro. Increase of radiation doses to the recipients to 10.40 Gy resulted in 100% survival and 100% donor-type lymphohemopoiesis in both groups of chimeras. These results indicate strongly that a genetic difference in radiosensitivity of immune system of the recipients can greatly influence the magnitude of residual HVG reactions observed in hybrid to parental strain bone marrow transplantation in mice. 相似文献