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J W Orr  A C Newton 《Biochemistry》1992,31(19):4667-4673
The roles of specific and nonspecific interactions in the regulation of protein kinase C by lipid have been examined. Binding and activity measurements reveal two mechanisms by which protein kinase C interacts with membranes: (1) a specific binding to the activating lipid phosphatidylserine and (2) a nonspecific binding to nonactivating, acidic lipids. The specific interaction with phosphatidylserine is relatively insensitive to ionic strength, surface charge, and the presence of nonactivating lipids. The two second messengers of the kinase, diacylglycerol and Ca2+, increase markedly the affinity of the kinase for phosphatidylserine. In contrast, the nonspecific interaction is sensitive to ionic strength and surface charge, and is unaffected by diacylglycerol. These results suggest that electrostatic interactions promote the binding of protein kinase C to membranes but the cooperative and selective binding of phosphatidylserine is the dominant driving force in a productive protein-lipid interaction.  相似文献   
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J W Orr  A C Newton 《Biochemistry》1992,31(19):4661-4667
The basis for the apparent cooperativity in the activation of protein kinase C by phosphatidylserine has been addressed using proteolytic sensitivity, resonance energy transfer, and enzymatic activity. We show that binding of protein kinase C to detergent-lipid mixed micelles and model membranes is cooperatively regulated by phosphatidylserine. The sigmoidal dependence on phosphatidylserine for binding is indistinguishable from that observed for the activation of the kinase by this lipid [Newton & Koshland (1989) J. Biol. Chem. 264, 14909-14915]. Thus, protein kinase C activity is linearly related to the amount of phosphatidylserine bound. Furthermore, under conditions where protein kinase C is bound to micelles at all lipid concentrations, activation of the enzyme continues to display a sigmoidal dependence on the phosphatidylserine content of the micelle. This indicates that the apparent cooperativity in binding does not arise because protein kinase C senses a higher concentration of phosphatidylserine once recruited to the micelle. Our results reveal that the affinity of protein kinase C for phosphatidylserine increases as more of this lipid binds, supporting the hypothesis that a domain of phosphatidylserine is cooperatively sequestered around the enzyme.  相似文献   
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The gorgoniid Eugorgia is exclusively an eastern Pacific genus. It has a wide geographic and bathymetric range of distribution, found from California to Perú and extends down to 65 m deep. Two new species are herein described. The morphological characters were analyzed and illustrated by light and scanning electron microscopy. Eugorgia beebei sp. n. can be distinguished by its white, ascending, sparse colony growth. Eugorgia mutabilis sp. n. can be distinguished by its white colony that changes color after collection, and the conspicuous sharp-crested disc sclerites. From a morphological point of view the new species are related to the daniana-group, the rubens-group and the siedenburgae-group of Eugorgia; their affiliations, and the proposal of a new group are discussed. These new species increases the number of species in the genus to 15, and contribute to the knowledge of the eastern Pacific octocoral biodiversity.  相似文献   
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Interactions between water availability and elevated atmosphericCO2 concentrations have the potential to be important factorsin determining future forage supply from temperate pastures.Using large turves from an established pasture, the responseof these communities at 350 or 700 l l–1 CO2 to a soilmoisture deficit and to recovery from the deficit in comparisonto turves that were well-watered throughout was measured. Priorto this experiment the turves had been exposed to the CO2 treatmentsfor 324 d. Net CO2 exchange continued at elevated CO2 even when the volumetricsoil moisture content was less than 0.10 m3 m–3 soil;at the same moisture deficit gas exchange at ambient CO2 waszero. The additional carbon fixed by the elevated CO2 turveswas primarily allocated below-ground as shown by the maintenanceof root length density at the same level as in well-wateredturves. When the dry turves were rewatered there was compensatorygrowth at ambient CO2 so that the above-ground growth rate exceededthat of turves that had not experienced a moisture deficit.At the start of this experiment, the turves that were growingat 700 l I–1 CO2 had a greater proportion of legume (principallywhite clover, Trifolium repens L.) in the harvested herbage.There was a trend for the legume content at elevated CO2 tobe reduced under a soil moisture deficit. The results indicate different strategies in response to soilmoisture deficits depending on the CO2 concentration. At ambientCO2, growth stopped, but plants were able to respond stronglyon rewatering; while at elevated CO2 growth continued (particularlybelow-ground), but no additional growth was evident on rewatering.Ecosystem gas exchange measurements taken at the end of theexperiment (after 429 d of exposure to CO2) showed 33% moreCO2 was fixed at elevated CO2 with only a small (12%) and nonsignificantdownward regulation. Key words: Carbon dioxide, climate change, grassland, gas exchange, soil moisture deficit  相似文献   
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Birds use change in daylength during the year to time events during their annual cycles. Individual Eurasian siskins Carduelis spinus can breed and winter in widely separated areas in different years. Birds at different latitudes will experience different changes in photoperiod. So how does latitude affect photoperiodic control? Our aim in this study was to find whether Siskins caught from the wild in Britain and exposed to different photoperiodic regimes, typical of widely separated latitudes, would differ in the subsequent timing and duration of their moults and associated processes. Siskins were caught in late February and early March, and initially kept outside on natural photoperiods. From the spring equinox (21 March), they were divided into three groups kept under photoperiodic regimes that simulated latitudes 40°, 55° and 70°N respectively. All three groups showed highly significant subsequent changes in body mass, fat scores and cloacal protuberance size. Moult of the primary feathers started during June – August (mean 9 July), and lasted 61–99 days (mean 75 days). Birds that started to moult late in the season had shorter moult durations. All individuals showed lower mass and fat levels during moult than before or after moult. Crucially, there were no significant differences in the timing of these events between the three photoperiodic groups. Apparently these birds did not use prevailing absolute photoperiod or the prevailing rate of change in photoperiod to time moult‐related seasonal events, but used instead some other feature of the annual photoperiod cycle or some form of interval timer linked to photoperiod.  相似文献   
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