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41.
A 14-kilodalton inner membrane protein of Vibrio cholerae biotype e1 tor confers resistance to group IV choleraphage infection to classical vibrios. 下载免费PDF全文
Choleraphage phi 149 differentiates the two biotypes, classical and el tor, of Vibrio cholerae. This phage cannot replicate in V. cholerae biotype el tor cells because the concatemeric DNA intermediates produced are unstable and cannot be chased to mature phage DNA. A V. cholerae biotype el tor gene coding for a 14,000-Da inner membrane protein which destabilizes the concatemeric DNA intermediates by hindering their binding to the cell membrane has been identified. Presumably, a 22,000-Da V. cholerae biotype el tor protein might also have a role in conferring phage phi 149 resistance to cells belonging to the biotype el tor. A nucleotide sequence homologous to the 1.2-kb V. cholerae biotype el tor DNA coding for both the 14,000- and 22,000-Da proteins is present in all strains of classical vibrios but is not transcribed. The nucleotide sequence of the gene coding for the 14,000-Da protein has been determined. 相似文献
42.
Efficiency of homologous intermolecular recombination at different locations on the Bacillus subtilis chromosome. 下载免费PDF全文
The efficiencies of intermolecular recombination at 12 different locations on the Bacillus subtilis chromosome were determined by transforming competent cells with a nonreplicative plasmid. The efficiencies varied by only about threefold but were significantly different (P less than 0.05 by a chi-square test) for approximately 20% of the locations. The recA gene product is required for recombination, and the addA gene product appears to affect the variation in a site-specific way. 相似文献
43.
Rats were exposed intermittently for 8h per day over 6 days at simulated high altitude of 20 000 feet. One group of altitude-exposed animals was treated with naproxen, a prostaglandin inhibiting drug. Significant reduction in body weight gain was observed in both altitude-exposed and drug-treated altitude-exposed animals compared to the control group. Right and left ventricular weights and weights of the adrenal glands were increased significantly in altitude-exposed and altitude-exposed drug-treated animals. The weight of the spleen was increased significantly in altitude-exposed animals whereas no such increase of splenic weight was observed in drug-treated altitude-exposed group of animals. On the other hand, the weight of the liver was decreased significantly in both cases. In drug-treated altitude-exposed animals, the unaltered splenic weight was thought to be due to inhibition of the erythropoietic activity. 相似文献
44.
Production, purification, and characterization of xylanase from a hyperxylanolytic mutant of Aspergillus ochraceus 总被引:2,自引:0,他引:2
Enhancement of the productivity of xylanase and beta-xy-losidase of Aspergillus ochraceus was investigated by multistep mutagenesis. The spores of the wild strain were subjected to UV and N-methyl-N-nitro-N-nitro-soguanidine (NTG). The hyperxylanolytic mutant (NG-13), which showed good clearing on the surface of the xylan-agar plate, secretes xylanase and beta-xylosidase at high levels during growth on commercial xylan and on agricultural wastes. Both liquid and solid state cultures were employed in the study for enzyme production. The xylanase from NG-13 was purified to homogeneity by ammonium sulfate precipitation and gel filtration. This purified enzyme showed a pH optimum of 6.0 and was stable in the range of pH 5 to 10. Prolonged stability of the enzyme was observed at 45 degrees C though its activity was maximal at 50 degrees C. The molecular weight of the enzyme was estimated to be 4.3 x 10(4) by SDS-polyacrylamide gel electrophoresis and 5 x 10(4) by gel filtration on Sephadex G-75. The kinetic data showed that the K(m) and V(max) values for xylan were 1 x 10(-3)M and 19.6 mumol/ min/mg protein, respectively. The enzyme was both more active and thermostable in the presence of K(+)and was inactivated by thiol reagents such as Hg(2+), p-hydroxymercuribenzoate (PHMB), 3', 5'-dithiobis (2'-nitrobenzoic acid) (DTNB), and N-ethylmaleimide (NEM). 相似文献
45.
Purification and properties of cyclic AMP-dependent protein kinase from rat epididymis 总被引:1,自引:0,他引:1
Two protein kinases (I and II: EC 2.7.1.37) that show a high degree of substrate specificity for protamine rather than histones, phosvitin and casein were partly purified from rat epididymal tissue. The enzymes were present in the cytosol because greater than 80% of the enzymic activity was recovered in the soluble fraction. The kinases required Mg2+ for activity although Co2+ and Mn2+ were partial substitutes. Zn2+ (1 mM) inhibited nearly completely the activity of the enzymes. Both the kinases showed high affinity for activation with cyclic AMP compared to other cyclic nucleotides. Amino acid analysis of 32P-labelled protamine product revealed that the kinases transfer the terminal phosphate of ATP to serine residues of the protein. The isoenzymes I and II showed certain differences in relation to their hydroxyapatite-chromatography profiles, pH activation profiles, heat sensitivity and Km for ATP and cyclic AMP. 相似文献
46.
Phosphoinositol kinase, the key enzyme responsible for the biosynthesis of higher inositol phosphates has been isolated from the cotyledons of mung beans germinated for 24 hr and has been resolved into two different forms, phosphoinositol kinase A and phosphoinositol kinase B. Both forms were purified to homogeneity and characterized. The Km values for ATP with phosphoinositol kinase A (1.78 × 10?4 M) and phosphoinositol kinase B (3.12 × 10 ?5 M) showed that phosphoinositol kinase B had a greater affinity for ATP. ATP could be partially replaced as phosphate donor by UTP and phosphoenolpyruvate in the case of phosphoinositol kinase A but not in the case of phosphoinositol kinase B. 相似文献
47.
The whole plant of Swertia hookeri, collected at flowering has been shown to contain two tri- and nine tetraoxygenated free, glucosyloxy, and stearyl ester xanthones and one flavonol stearyl ester. Among these, three are previously unreported in nature and one was known previously only as a synthetic compound. The xanthones are based on 1,3,5,-, 1,3,5,8- and 1,3,7,8-oxygenated systems with the middle oxygenation pattern predominating. The two ester compounds appeared only at the flowering stage. Plants collected at the pre-flowering stage gave the corresponding free compounds. The biochemical and biological significance of these findings are appraised. 相似文献
48.
N-Acetylmannosamine kinase activity is absent from yeast cells grown on N-acetylmannosamine. However, other enzymes of the catabolic pathway, namely, N-acetylmannosamine-2-epimerase, N-acetylglucosamine kinase and glucosamine-6-phosphate deaminase are induced. In addition, a high affinity uptake system (permease) for the uptake of N-acetylglucosamine is synthesized under these conditions. The presence of either N-acetylmannosamine or N-acetylglucosamine as inducer is essential for the induced synthesis of these enzymes. The enzyme synthesis stops and their concentration in the cells declines rapidly as soon as inducer is removed from the medium. N-Acetyl-D-galactosamine can also induce all these enzymes except for N-acetylmannosamine-2-epimerase, suggesting the convergence of catabolic pathways for both the aminosugars at N-acetyl-D-glycosamine. Experiments with inhibitors of macromolecule synthesis suggest that the snythesis of RNA and protein is necessary for the induction of these cyzymes whereas the synthesis of DNA is not. 相似文献
49.
50.
The rate of RNA synthesis and its inhibition by α-amanitin in the nuclei of mature and immature avian erythrocytes are increased
with the increase in ionic strength of incubation medium. Polyacrylamide gel electrophoresis indicates that heterogeneous
species of RNAs are synthesised in the mature and immature erythrocyte nuclei. However, a large number of high molecular weight
RNAs are synthesised in the nuclei of immature erythrocytes. Elution profiles on poly(U)-sepharose chromatography indicate
that the RNAs synthesised in the nuclei of two types of cell contain poly(A) segments. Sixteen per cent of mature erythrocyte
nuclear RNA syntbesised are polyadenylated, while it is 13% in immature erythrocyte nuclei. However, the total RNA synthesised
is 2–3 fold higher in immature erythrocyte nuclei than that in mature erythrocyte nuclei. 相似文献