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1.
Salil K. Niyogi Thomas S. Soper Robert S. Foote Frank W. Larimer Richard J. Mural Sankar Mitra Eva H. Lee Richard Machanoff Fred C. Hartman 《Journal of biosciences》1987,11(1-4):203-214
Both Lys-166 and His-291 of ribulosebisphosphate carboxylase/oxygenase fromRhodospirillum rubrum have been implicated as the active-site residue that initiates catalysis. To decide between these two candidates, we resorted
to site-directed mutagenesis to replace Lys-166 and His-291 with several amino acids. All 7 of the position-166 mutants tested
are severely deficient in carboxylase activity, whereas the alanine and serine mutants at position 291 are ∼40% and ∼18% as
active as the native carboxylase, essentially ruling out His-291 in theRhodospirillum rubrum carboxylase (and by inference His-298 in the spinach enzyme) as a catalytically essential residue. The ability of some of
the mutant proteins to undergo carbamate formation or to bind either ribulosebisphosphate or a transition-state analogue remains
largely unimpaired. This implies that Lys-166 is not required for substrate binding; rather, the results corroborate the earlier
postulate that Lys-166 functions as an acid-base group in catalysis or in stabilizing a transition state in the reaction pathway. 相似文献
2.
Detailed molecular analysis of three wild-derived MHC haplotypes provided evidence for an important role of the E beta recombinational hot spot in the recent evolution of the mouse I region. Examination of RFLP and restriction maps of cloned DNA permitted the mapping of the natural cross-over events in the haplotypes carried by strains B10.GAA37 (w21) and B10.KPB128 (w19) to a fragment of DNA not exceeding 4.1 kb, which lies almost entirely within the intron separating the beta 1 and beta 2 exons of the E beta gene. In the w14 haplotype (strain B10.STC77), which appears to be a natural recombinant between a p-like parental haplotype and another wild-derived haplotype, the site of crossing over can be mapped to a segment between the beta 2 exon of the E beta gene (left border) and the E beta 2 gene (right border). This segment containing the cross-over site in the w14 haplotype includes the E beta hot spot. In addition, the w14 haplotype as well as the standard p haplotype contain a deletion of approximately 1.0 kb in the second intron of the E beta gene, which may represent the product of an unequal cross-over event in a E beta recombinational hot spot. 相似文献
3.
Properties of Venezuelan Equine Encephalomyelitis Virus Accompanying Attenuation In Vitro 总被引:4,自引:2,他引:2
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Virus obtained during serial plaque passage of the virulent parent egg seed (PES) of the Trinidad strain of Venezuelan equine encephalomyelitis (VEE) virus produced only large plaques during either 3 serial plaque passages in chick fibroblasts or 10 plaque passages in L cells, and was lethal for mice by the intraperitoneal route. Virus showing these characteristics was designated the stable large-plaque (Ls) type. In contrast, virus obtained during serial plaque passage of the attenuated 9t strain in chick fibroblasts formed only very small plaques and was not lethal for mice by the intraperitoneal route. Virus showing these properties was designated the stable small-plaque (Ss) type. Under other passage conditions, however, large-plaque virus that yielded about 90% large and 10% small plaques was obtained; this virus was designated the unstable large or Lu type because it differed from the Ls type, which yielded only large plaques. The Lu type continued to yield the same ratio of large to small plaques for several plaque-to-plaque passages. In addition, small-plaque virus that yielded both large and small plaques and that showed a reduced capability to infect mice was also recovered. This virus was designated the unstable small or Su type because it differed from the Ss type in its higher level of virulence and in its plaque-forming properties. Thus, based upon the properties of virulence for mice and plaque size, four viral types could be discerned. The evidence suggests that serial passage in cell culture imposed environmental pressures that sequentially selected the following viral types: Ls, Lu, Su, and Ss. 相似文献
4.
5.
An infant, born to unrelated parents, who had a rugated perineal mass which measured 17 cm in diameter is reported. No external genitalia or anal orifice was identified although the infant voided from a 5 mm crevice on the caudal surface of the mass. The patient died at four weeks of age. The perineal mass was made up of two separate sacs. The anterior sac resembled a urinary bladder in which two ureteral and a single vaginal orifice were identified. The posterior sac was continuous with the peritoneal cavity and contained bowel, left ovary, uterus and right kidney. The left kidney was small, polycystic and the right gonad a streak. 相似文献
6.
A vacuum apparatus has been described that has enabled samples of bacterial spore suspensions to be dehydrated at defined temperatures between 0 and 65 °C, with facilities for reequilibration of the dried samples to aqueous vapor pressures between 5 × 10?4 and 10 torr and subsequent exposure to dry gases. The apparatus has been characterized using sample temperature/drying-time profiles, and drying rate/ drying-time curves, and the reproducibility of the dehydration and rehydration techniques has been established. Biological data have confirmed the suitability of the apparatus since no loss of spores from samples has been observed during any of these experimental treatments. On the basis of measurements recorded during rehydration of dried spores, it is suggested that dehydration occurs at specific sites in the spore which are of two types, 1) reversibly dehydrated (rehydratable) and 2) irreversibly dehydrated (nonrehydratable). 相似文献
7.
8.
The distribution of PGE2 binding sites in four subcellular fractions (F1-F4) from porcine fundic mucosa obtained by gradient centrifugation was examined. Binding of 3HPGE2 to fractions F2-F4 was specific, dissociable, saturable and pH dependent. A significant degree of specific binding was not evident in F1. The Scatchard analysis of binding to F2 and F3 revealed heterogenous populations of binding sites with similar dissociation constants but greater concentrations of binding sites than was evident in the initial 30,000 xg homogenate protein. A single class of low affinity binding sites was evident in F4. The ratio of total: nonspecific binding was approximately equal in F2 and F3. The ratio was considerably smaller in F4. The activity of 5' nucleotidase the marker enzyme for plasma membranes followed this ratio. There was no correlation between the binding ratio and marker enzyme activities for mitrochondrial membranes and endoplasmic reticulum. These data suggest that high affinity PGE2 binding sites occur predominantly on the plasma membrane from gastric mucosal tissue. 相似文献
9.
Under the Red Queen hypothesis, outcrossing can produce genetically variable progeny, which may be more resistant, on average, to locally adapted parasites. Mating with multiple partners may enhance this resistance by further increasing the genetic variation among offspring. We exposed Potamopyrgus antipodarum to the eggs of a sterilizing, trematode parasite and tested whether this altered mating behaviour. We found that exposure to parasites increased the number of snail mating pairs and the total number of different mating partners for both males and females. Thus, our results suggest that, in host populations under parasite-mediated selection, exposure to infective propagules increases the rate of mating and the number of mates. 相似文献
10.
Renu Goel Krishna R Murthy Srinivas M Srikanth Sneha M Pinto Mitali Bhattacharjee Dhanashree S Kelkar Anil K Madugundu Gourav Dey Sujatha S Mohan Venkatarangaiah Krishna TS Keshava Prasad Shukti Chakravarti HC Harsha Akhilesh Pandey 《Clinical proteomics》2013,10(1):9