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81.
An experiment is described in which the effects of age, previous infection, pregnancy and lactation on some reactions of cattle to infection with Ostertagia ostertagi were studied. It was found that an acquired resistance to the establishment of worms developed more rapidly in 20-month-old heifers than in calves, that it was unaffected by pregnancy of the host but that it was largely lost by heifers in early lactation. The rate at which populations were turned over, i.e. the mean life-span of worms through the late 4th and 5th stages was unaffected by the factors studied. Although, in the conditions of the experiment, development of the worms was not arrested in susceptible calves, both age of the host and its previous experience of infection were significant causes of arrest, and in previously infected 20-month-old cattle 86% of the worms of a challenge infection were arrested. Pregnancy did not affect the proportion of worms that was arrested but in lactating heifers only marginally more worms were arrested than in calves. Worms that were not arrested grew more rapidly in calves and in lactating heifers than in empty heifers or those in mid-pregnancy. 相似文献
82.
Monique Decastel Anh-Tuan Tran Jean-Pierre Frénoy 《Biochemical and biophysical research communications》1982,106(2):638-643
The binding of 4-methylumbelliferyl-α-D-galactopyranoside, -β-D-galactopyranoside and -D-Galβ(1→3)DGalNac to peanut agglutinin was studied by fluorescence. Peanut agglutinin quenched the fluorescence intensity of 4-methylumbelliferyl-α-D-galactopyranoside but enhanced that of the two 4-methylumbelliferyl-β-galactosides. For α-D-galactopyranoside, the association constants measured at 4 and 25°C were 3.4 × 103 and 1.7 × 103 M?1 respectively, and for D-Galβ(1→3)DGalNac, 1.5 × 105 and 3.3 × 104 M?1. The binding enthalpies estimated from these values are consistent with the existence of extended sugar binding sites in the peanut agglutinin molecule. 相似文献
83.
T Ohashi C M Hong S Weiler J M Tomich J M Aerts J M Tager J A Barranger 《The Journal of biological chemistry》1991,266(6):3661-3667
Human cDNA was mutagenized to duplicate six naturally occurring mutations in the gene for glucocere-brosidase. The mutant genes were expressed in NIH 3T3 cells. The abnormal human enzymes were purified by immunoaffinity chromatography and characterized. The Asn370----Ser mutant protein differed from normal enzyme in its inhibition by both conduritol B epoxide and glucosphingosine demonstrating that the 370 mutant enzyme has an abnormal catalytic site. In addition, the 370 mutant enzyme is less activated by saposin C, but more stimulated by phosphatidylserine than the wild type enzyme. The Arg463----Cys mutant protein was normal with respect to conduritol B epoxide and glucosphingosine inhibition, but was less activated by both saposin C and phosphatidylserine. The Arg120----Gln mutant protein was catalytically inactive. The Leu444----Pro, the pseudopattern, and the Pro415----Arg mutants appear to have reduced amounts of enzyme protein in cells. The studies demonstrated that mutations in the gene for glucocerebrosidase have different effects on the catalytic activity and stability of the enzyme. 相似文献
84.
An alternative to estimation of cell growth kinetics via continuous culture experiments is proposed in this article. The method employed is based on batch culture experiments with very small inocula (initial cell concentrations being typically less than 5000 cells/mL). Such low initial cell concentrations result in extended exponential cell growth phase during which culture conditions remain unchanged, thereby permitting precise estimation of specific cell growth rates from batch experiments especially for fast-growing microorganisms such as Bacillus species. The effectiveness and utility of this approach are demonstrated via several experiments conducted with a wild-type strain (Bacillus subtilis TN106) and a recombinant strain (B. subtilis TN106[pAT5]). True establishment of exponential growth phase requires insignificant variance of most of the culture conditions during the initial growth phase. Satisfaction of this requirement is demonstrated for microbial systems investigated here. This approach is especially well suited for recombinant microorganisms containing segregationally unstable plasmids, since estimation of growth kinetics of these from continuous cultures is very difficult and highly unreliable due to continual reversion of recombinant ceils to plasmid-free host cells unless some selection pressure is applied at levels sufficient to keep the presence of plasmid-free cells minimal. 相似文献
85.
Engineering a Bacillus subtilis expression-secretion system with a strain deficient in six extracellular proteases. 总被引:14,自引:2,他引:12 下载免费PDF全文
We describe the development of an expression-secretion system in Bacillus subtilis to improve the quality and quantity of the secreted foreign proteins. This system consists of a strain (WB600) deficient in six extracellular proteases and a set of sacB-based expression vectors. With the inactivation of all six chromosomal genes encoding neutral protease A, subtilisin, extracellular protease, metalloprotease, bacillopeptidase F, and neutral protease B, WB600 showed only 0.32% of the wild-type extracellular protease activity. No residual protease activity could be detected when WB600 was cultured in the presence of 2 mM phenylmethylsulfonyl fluoride. By using TEM beta-lactamase as a model, we showed that WB600 can significantly improve the stability of the secreted enzyme. To further increase the production level we constructed an expression cassette carrying sacY, a sacB-specific regulatory gene. This gene was placed under the control of a strong, constitutively expressed promoter, P43. With this cassette in the expression vector, an 18-fold enhancement in beta-lactamase production was observed. An artificial operon, P43-sacY-degQ, was also constructed. However, only a partial additive enhancement effect (24-fold enhancement) was observed. Although degQ can stimulate the production of beta-lactamase in the system, its ability to increase the residual extracellular protease activity from WB600 limits its application. The use of the P43-sacY cassette and WB600 would be a better combination for producing intact foreign proteins in high yield. 相似文献
86.
兔出血症病毒核酸的某些理化性质的研究 总被引:1,自引:0,他引:1
本文对我国无锡分离的兔出血症病毒A_2R-3毒株核酸的某些理化性质进行了研究。采用孚尔根染色、二苯胺反应和核酸酶解实验证实病毒核酸为DNA类型。吖啶橙染色、甲醛反应、核酸酶S_1消化和核酸热变性实验表明病毒核酸为单链型。核酸电泳呈单一组分。电境观察显示核酸分子链呈线状,平均长度约为2.15μ。计算分子量约为2.1—2.5×10~6d。核酸碱基组盛为A25.34、T29.37、G23.85、C21.43、(G C)克分子百分比值为45.28。结合以前的报道、我们认为:兔出血症病毒可以归类于细小病毒科。 相似文献
87.
The transmembrane domain of N-glucosaminyltransferase I contains a Golgi retention signal. 总被引:6,自引:0,他引:6
The enzyme N-acetylglucosaminyltransferase I (NT, EC 2.4.1.101) is a resident type II transmembrane protein of the Golgi apparatus. To delineate the portion of its primary sequence that is responsible for the Golgi retention of this protein, we constructed chimeras containing different N-terminal portions of NT joined to a reporter sequence, the ectodomain of a type II surface membrane protein. These chimeric proteins were found to be retained in the Golgi apparatus as assessed by cell surface biotinylation and immunofluorescence. We found that the transmembrane domain of NT is sufficient to confer Golgi retention of the fusion proteins and propose that it contains the Golgi retention signal of the parent molecule. 相似文献
88.
Y Ishimi E Abe C H Jin C Miyaura M H Hong M Oshida H Kurosawa Y Yamaguchi M Tomida M Hozumi 《Journal of cellular physiology》1992,152(1):71-78
Leukemia inhibitory factor/differentiation-stimulating factor (LIF/D-factor), expression of its mRNA, and possible roles in bone metabolism were studied in murine primary and clonal osteoblast-like cells. Local bone-resorbing factors such as IL-1, TNF alpha, and LPS strongly induced expression of LIF/D-factor mRNA in both clonal MC3T3-E1 cells and primary osteoblast-like cells. Neither parathyroid hormone nor 1 alpha,25-dihydroxyvitamin D3 stimulated expression of LIF/D-factor mRNA. LIF/D-factor per se did not stimulate expression of its own mRNA. Appreciable amounts of LIF/D-factor were detected in synovial fluids from rheumatoid arthritis (RA) patients but not in those with osteoarthritis (OA). Simultaneous treatment with LIF/D-factor, IL-1, and IL-6 at the concentrations found in synovial fluids from RA patients greatly enhanced bone resorption, though these cytokines did not stimulate bone resorption when separately applied. This suggests that LIF/D-factor produced by osteoblasts is in concert with other bone-resorbing cytokines such as IL-1 and IL-6 involved in the bone resorption seen in the joints of RA patients. LIF/D-factor specifically bound to MC3T3-E1 cells with an apparent dissociation constant of 161 pM and 1,100 binding sites/cell. LIF/D-factor dose-dependently suppressed incorporation of [3H]thymidine into MC3T3-E1 cells. In addition, it potentiated the alkaline phosphatase activity induced by retinoic acid, though LIF/D-factor alone had no effect on enzyme activity. These results suggest that LIF/D-factor is involved in not only osteoclastic bone resorption but also osteoblast differentiation in conjugation with other osteotropic factors. 相似文献
89.
90.
Soluble luminal proteins of the endoplasmic reticulum (ER) are known to be retained by a tetrapeptide retention signal, KDEL. We report in this communication that the KDEL sequence when appended to the carboxy terminus of a cell surface membrane protein, dipeptidyl peptidase IV (DPPIV), resulted in its retention in the endoplasmic reticulum of transfected Madin-Darby canine kidney cells as assessed by indirect immunofluorescence. Selective surface biotinylation revealed that about 90-95% of the expressed DPPIV was retained in the ER. Appendance of the sequence KDEV did not, however, result in ER retention, illustrating the functional specificity of the retention signal. The ER retention was not due to misfolding of the mutant protein, as the mutant proteins remained enzymatically active. Our data suggest that the KDEL receptor is able to recognize and recycle type II membrane proteins containing a carboxyl-terminal KDEL sequence and postulates the existence of such yet to be identified endogenous proteins. 相似文献