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991.
The synthesis of some monocyclic beta-lactams (monobactams) by the Staudinger reaction using D-glucosamine propanedithioacetal as chiral auxiliary is reported. The influence of several radicals at C3, C4, and C1' (sugar moiety) as well as other structural aspects are considered in relation to the antielastase activity. 相似文献
992.
Kinga Michno David Knight Jorge M. Campussano Diana van de Hoef Gabrielle L. Boulianne 《PloS one》2009,4(9)
Much of our current understanding about neurodegenerative diseases can be attributed to the study of inherited forms of these disorders. For example, mutations in the presenilin 1 and 2 genes have been linked to early onset familial forms of Alzheimer''s disease (FAD). Using the Drosophila central nervous system as a model we have investigated the role of presenilin in one of the earliest cellular defects associated with Alzheimer''s disease, intracellular calcium deregulation. We show that expression of either wild type or FAD-mutant presenilin in Drosophila CNS neurons has no impact on resting calcium levels but does give rise to deficits in intracellular calcium stores. Furthermore, we show that a loss-of-function mutation in calmodulin, a key regulator of intracellular calcium, can suppress presenilin-induced deficits in calcium stores. Our data support a model whereby presenilin plays a role in regulating intracellular calcium stores and demonstrate that Drosophila can be used to study the link between presenilin and calcium deregulation. 相似文献
993.
J W Wray W A Baase J D Lindstrom L H Weaver A R Poteete B W Matthews 《Journal of molecular biology》1999,292(5):1111-1120
The mutation Glu108-->Val (E108V) in T4 lysozyme was previously isolated as a second-site revertant that specifically compensated for the loss of function associated with the destabilizing substitution Leu99-->Gly (L99G). Surprisingly, the two sites are 11 A apart, with Leu99 in the core and Glu108 on the surface of the protein. In order to better understand this result we have carried out a detailed thermodynamic, enzymatic and structural analysis of these mutant lysozymes as well as a related variant with the substitution Leu99-->Ala. It was found that E108V does increase the stability of L99G, but it also increases the stability of both the wild-type protein and L99A by essentially equal amounts. The effects of E108V on enzymatic activity are more complicated. The mutation slightly reduces the maximal rate of cell wall hydrolysis of wild-type, L99G and L99A. At the same time, L99G is an unstable protein and rapidly loses activity during the course of the assay, especially at temperatures above 20 degrees C. Thus, even though the double mutant L99G/E108V has a slightly lower maximal rate than L99G, over a period of 20-30 minutes it hydrolyzes more substrate. This decrease in the rate of thermal inactivation appears to be the basis of the action of E108V as a second-site revertant of L99G. Mutant L99A creates a cavity of volume 149 A(3). Instead of enlarging this cavity, mutant L99G results in a 4-5 A displacement of part of helix F (residues 108-113), creating a solvent-accessible declivity. In the double mutant, L99G/E108V, this helix returns to a position akin to wild-type, resulting in a cavity of volume 203 A(3). Whether the mutation Glu108-->Val is incorporated into either wild-type lysozyme, or L99A or L99G, it results in a decrease in crystallographic thermal factors, especially in the helices that include residues 99 and 108. This increase in rigidity, which appears to be due to a combination of increased hydrophobic stabilization plus a restriction of conformational fluctuation, provides a structural basis for the increase in thermostability. 相似文献
994.
995.
Analysis of the fine specificity and cross-reactivity of monoclonal anti-lipid A antibodies 总被引:3,自引:0,他引:3
T N Kirkland D E Colwell S M Michalek J R McGhee E J Ziegler 《Journal of immunology (Baltimore, Md. : 1950)》1986,137(11):3614-3619
We have investigated the fine specificity of anti-lipid A antibodies to identify conserved lipid A antigens. Because lipid A derived from many different Gram-negative bacteria has similar biologic activities, the conserved regions may be of particular importance for the immunostimulatory and toxic properties of lipid A. We found that five of nine antibodies bound to a wide variety of Gram-negative bacteria. All these widely cross-reactive antibodies bound to the same antigenic site within lipid A. Polymyxin B, an inhibitor of lipid A activity, bound to this site as well. The widely cross-reactive antibodies bound to native and base-hydrolyzed lipid A equally well, and also bound to the monosaccharide precursor lipid X. The less cross-reactive antibodies recognized base-hydrolyzed lipid A poorly, and did not recognize lipid X at all. Other investigators have shown that lipid X has some of the activities of lipid A in vitro and can inhibit the lethal toxicity of LPS in vivo. On the basis of this study, we suggest that lipid X contains a conserved lipid A epitope as well. 相似文献
996.
The photometric assay of reducing sugars with 2,2'-bicinchoninate was improved and its conditions were optimized. Optical density is linear between 1 and 25 nmol sugar/sample, and the assay is not affected by borate, phosphate, or other buffer anions. The molar extinction coefficients produced by the standard procedure with the 12 most common monosaccharides occurring in carbohydrates and conjugated glycocompounds are listed. 相似文献
997.
L Takemoto J Smith T Kodama 《Biochemical and biophysical research communications》1987,142(3):761-766
Polyclonal antisera to three synthetic peptides of bovine MIP26K have been used in combination with Western blot analysis to probe for changes of the MIP26K molecule during human senile cataractogenesis. Anti-MIP26K229-237 binds well to the 26K component from cataractous lens membranes, but binds poorly to the same component from normal lens. In contrast, antisera to two other sequences of MIP26K (anti-MIP26K252-259 and anti-MIP26K256-263) bind approximately equally well to the 26K component from either cataractous or normal lens. Together, these results demonstrate that during cataract development there is a selective covalent change in a region of the MIP26K molecule that may have profound effects upon the ability of this molecule to facilitate intercellular communication between lens fiber cells. 相似文献
998.
999.
Erythrocyte isozymes of phosphofructokinase in genetically high- and low-2,3-diphosphoglycerate rats
N. A. Noble L. H. Kuwashima T. T. Togioka K. R. Tanaka 《Biochemical genetics》1982,20(11-12):1055-1065
A major locus (Dpg) with two alleles (d and D) controls erythrocyte 2,3-diphosphoglycerate (DPG) levels in Long-Evans rats and is closely linked to a locus (Hbb) determining a hemoglobin electrophoretic polymorphism. Glycolytic intermediate levels and phosphofructokinase (PFK) kinetic studies suggest that in vivo PFK activity differences underlie the differences in DPG levels. We report here chromatographic and immunologic evidence that rat erythrocyte PFK is composed of two isozymes which elute from DEAE-Sephadex at positions identical to those of the isozymes in platelets and liver, respectively. The percentage of platelet-type PFK is significantly (P less than 0.05) smaller in low-DPG (dd) hemolysates than in DD hemolysates regardless of hemoglobin phenotype. When hemolysates were prepared in a stabilizing buffer, PFK specific activity was significantly (P less than 0.005) higher in DD rats. These data suggest that the PFK kinetic differences may result from alterations in the isozyme composition of active PFK. 相似文献
1000.
A common DNA religation assay for topoisomerase II takes advantage of the fact that the enzyme can rejoin cleaved nucleic acids but cannot mediate DNA scission at suboptimal temperatures (either high or low). Although temperature-induced DNA religation assays have provided valuable mechanistic information for several type II enzymes, high-temperature shifts have not been examined for human topoisomerase IIalpha. Therefore, the effects of temperature on the DNA cleavage/religation activity of the enzyme were characterized. Human topoisomerase IIalpha undergoes two distinct transitions at high temperatures. The first transition occurs between 45 and 55 degrees C and is accompanied by a 6-fold increase in the level of DNA cleavage at 60 degrees C. It also leads to a loss of DNA strand passage activity, due primarily to an inability of ATP to convert the enzyme to a protein clamp. The enzyme alterations that accompany the first transition appear to be stable and do not revert at lower temperature. The second transition in human topoisomerase IIalpha occurs between 65 and 70 degrees C and correlates with a precipitous drop in the level of DNA scission. At 75 degrees C, cleavage falls well below amounts seen at 37 degrees C. This loss of DNA scission appears to result from a decrease in the forward rate of DNA cleavage rather than an increase in the religation rate. Finally, similar high-temperature alterations were observed for yeast topoisomerase II and human topoisomerase IIbeta, suggesting that parallel heat-induced transitions may be widespread among type II topoisomerases. 相似文献