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1. Conformational motility of the purified muscle glycogen phosphorylase B from two species of vertebrates (rabbit and frog) was investigated by the Hydrogen-Exchange method and Infrared Spectometry. 2. The experimental results of the 1H-2H exchange were expressed in terms of the probability P of exposure to isotopic solvent of phosphorylase peptide groups and in terms of the corresponding changes in standard free energy delta Go. 3. The combined methods used didn't show considerable differences of the protein conformations in the physiological pH region but rabbit phosphorylase was only characterized by rather more compact structure in comparison with frog phosphorylase. 相似文献
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The relationship between nucleolar and mitotic cycles has beendetermined after treatment of root apices of Zea mays with ethidiumbromide. In the meristematic regions of the stele the two cyclesare not much displaced in relation to each other except fora delay in the onset of the disorganization phase. A few nucleolipersist into metaphase and a few nuclei undergo an amitoticdivision. In the cap initials the drug greatly delays the onsetof disorganization of the nucleolus, which normally occurs beforeprophase in this region. It also delays the completion of reorganizationso that fully organized nucleoli are no longer available duringthe last half of telophase. In the quiescent centre the onsetof disorganization and the end of reorganization of the nucleoliare also delayed in relation to mitosis. There is no evidencefor a delay in the onset of reorganization in any region ofthe meristem. Some cells form multiple micronucleoli and this aberrant behaviouroccurs more often in the cap initials than elsewhere as doesamitotic division. 相似文献
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Light, fluorescence and electron microscopical analysis of therooted freshwater plantRanunculus trichophyllusrevealed a peculiaranatomical feature. In addition to the true endodermis encirclingthe root stele, endodermis-like sheaths occurred around eachvascular bundle of the leaf segments and of the eustelic stemwith its large central cavity, which assumed an anatomical featureresembling that of some pteridophyte stems. These impermeablesheaths, whose cells differentiate suberized walls, can playa major role in hampering the apoplastic leakage of the pressurizedwater solution which flows throughout the plant in xylem vesselsand contains the mineral nutrients taken up by the roots fromthe sediment. Moreover, these sheaths can function in preventingflooding of the aerenchymatic cavities of the submerged organs.In this way the endodermis-like sheaths preserve the correctcirculation of gas and nutrient solution through the entireorganism and assume great significance as a structural mechanismevolved by this species to survive and grow underwater.Copyright1999 Annals of Botany Company. Ranunculus trichophyllus,freshwater macrophyte, submerged angiosperm, anatomy, endodermis, endodermis-like sheaths, light microscopy, fluorescence microscopy. 相似文献
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The mitochondrial DNA (mtDNA) of individuals from 79 colonies of Apis mellifera from five Canary Islands was studied using the Dra I test based on the restriction of PCR products of the tRNAleu–COII intergenic region. Five haplotypes of the African (A) lineage and one of the west European (C) lineage were found. The haplotypes A14 and A15 are described for the first time. These haplotypes have a new P sequence named P1 . The wide distribution and high frequency of haplotype A15 suggest that it is characteristic of the Canarian Archipelago. Sources of haplotype variability of honeybee mtDNA in the Canary Islands (waves of colonization from Africa, queen importations, habitat diversification) are discussed. 相似文献