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41.
42.
The regulation of amidase synthesis inP. aeruginosa is under positive control. This review describes the experimental evolution of amidase and its regulator protein for the hydrolysis of novel substrates and experiments to elucidate the mechanism of the control system. 相似文献
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44.
The ribulose-1,5-bisphosphate carboxylase (Rubisco) large- and small-subunit genes are encoded on the chloroplast genome of the eukaryotic chromophytic alga Olisthodiscus luteus. Northern blot experiments indicate that both genes are co-transcribed into a single (>6 kb) mRNA molecule. Clones from the O. luteus rbc gene region were constructed with deleted 5 non-coding regions and placed under control of the lac promoter, resulting in the expression of high levels of O. luteus Rubisco large and small subunits in Escherichia coli. Sucrose gradient centrifugation of soluble extracts fractionated a minute amount of carboxylase activity that cosedimented with native hexadecameric O. luteus Rubisco. Most of the large subunit synthesized in E. coli appeared insoluble or formed an aggregate with the small subunit possessing an altered charge: mass ratio compared to the native holoenzyme. The presence in O. luteus of a polypeptide that has an identical molecular mass and cross reacts with antiserum generated against pea large-subunit binding protein may indicate that a protein of similar function is required for Rubisco assembly in O. luteus. 相似文献
45.
In vitro enzyme activities of glycolysis, pentose-phosphate pathway and dark CO2 fixation were assayed in batch cultures of heterotrophic Catharanthus roseus cells under various gassing rates and partial pressures of carbon dioxide. Detrimental effects of low pCO2 culture conditions on the growth characteristics could be linked to marked changes in levels of enzymes of primary metabolism during growth. The enzyme levels observed during the early stages of growth were found to be more stable when a constant pCO2 (20 mbar) was maintained and enabled exponential growth to be reached more rapidly.The importance of carbon dioxide as a conditioning factor of the culture medium is discussed. 相似文献
46.
47.
The activity levels of enzymes of aromatic amino acid biosynthesis respond to changing physiological states of growth, as illustrated by results obtained from suspension-cultured cells of Nicotiana silvestris Speg. et Comes line ANS 1 (2N=24). The experimental system provides a foundation for interpretations about overall regulation of enzyme levels in relationship to growth physiology. Levels of activity for shikimate dehydrogenase (EC 1.1.1.25), prephenate aminotransferase and arogenate dehydrogenase were followed throughout a growth cycle obtained by a conventional subculture protocol. Enzyme date were also obtained from cell cultures maintained in continuous exponential growth for greater than 10 generations (EE cells). Both shikimate dehydrogenase and prephenate aminotransferase exhibited elevated stationary-phase levels of enzyme, much of which was carried over into a subsequent subculture. At least 4 generations of exponential growth were required before diminution of the latter two enzymes to the levels characteristic of truly exponential-phase growth (EE cells) occurred. This is reminiscent of the overall behavior of 3-deoxy-D- arabino -heptulosonate 7-phosphate (DAHP) synthase (EC 4.1.2.15), specifically attributed to the properties of the cytosolic isozyme species (DAHP synthase-Co). Elevation of arogenate dehydrogenase also occurred in stationary-phase cells, but diminished rapidly during lag phase to reach the level characteristic of EE cells. 相似文献
48.
The leaf ultrastructure of NADP-malic enzyme type C4 species possessing different anatomical features in the Cyperaceae was examined: types were the Rhynchosporoid type, a normal
Kranz type in which mesophyll cells are adjacent to Kranz cells, and Fimbristyloid and Chlorocyperoid types, unusual Kranz
types in which nonchlorophyllous mestome sheath intervenes between the two types of green cells. They show structural characteristics
basically similar to the NADP-malic enzyme group of C4 grasses, that is, centrifugally located chloroplasts with reduced grana and no increase of mitochondrial frequency in the
Kranz cells. However, the Kranz cell chloroplasts of the Fimbristyloid and Chlorocyperoid types exhibit convoluted thylakoid
systems and a trend of extensive development of peripheral reticulum, although those of the Rhynchosporoid type do not possess
such particular membrane systems. The suberized lamella, probably a barrier for CO2 diffusion, is present in the Kranz cell walls of the Rhynchosporoid type and in the mestome sheath cell walls of the other
two types, and tightly surrounds the Kranz cells (sheaths) that are the sites of the decarboxylation of C4 acids. These ultrastructural features are discussed in relation to C4 photosynthetic function. 相似文献
49.
猪肺血管紧张素转换酶的提纯 总被引:2,自引:0,他引:2
本文报道了猪肺血管紧张素转换酶(ACE)的提纯方法及其鉴定,并讨论了方法的改进。肺匀浆经1.6—2.6mol/L硫酸铵沉淀,Sephadex G-200凝胶过滤,DEAE-Sephaeel及羟基磷灰石柱层析步骤,从168克肺中获得4.5毫克酶蛋白纯品。活力回收45.2%,比活力15.6单位/毫克蛋白;和匀浆上清比较,提纯390倍。经聚丙烯酰胺凝胶电泳(pH8.3)鉴定为一条带。按SDS聚丙烯酰胺凝胶电泳(SDS-PAGE)测得其分子量为132,000道尔顿。酶蛋白在-30℃貯存10月,比活力丢失30%。 相似文献
50.
F Puvion-Dutilleul E Pichard 《Biology of the cell / under the auspices of the European Cell Biology Organization》1992,76(2):139-150
Formation of progeny viruses in the nuclei of HeLa cells infected with adenovirus type 5 was studied at the ultrastructural level by in situ hybridization techniques allowing specific detection of either viral double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA). Prior to the initiation of replication of viral genomes, infective DNA molecules which entered the nucleus of the target cell were randomly distributed among host chromatin fibers including nucleolus-associated chromatin. They were double-stranded, that is, without single-strand breaks. Such association of viral DNA with host condensed chromatin also occurred in mitosis. The initiation of viral genome replication occurred simultaneously with the appearance in the nucleoplasm of small fibrillar regions containing intermingled viral dsDNA and ssDNA. Later, at the intermediate stage of nuclear transformation, viral dsDNA and ssDNA molecules were almost entirely separated into two contiguous substructures. At this stage, viruses were observed occasionally in the vicinity of viral ssDNA accumulation sites. Still later, an additional substructure developed in the centre of the nucleus which consisted of large quantities of viral dsDNA, traces of viral ssDNA and abundant viruses. Portions of viral ssDNA were attached to some viruses even at late stage of nuclear transformation, an association which strongly suggests the occurrence of encapsidation of at least some of the viral genomes while they are still engaged in replication. 相似文献