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排序方式: 共有362条查询结果,搜索用时 667 毫秒
1.
A V Kabanov A L Klibanov V P Torchilin K Martinek A V Levashov 《Bioorganicheskaia khimiia》1987,13(10):1321-1324
The characteristics of water-soluble enzyme (alpha-chymotrypsin) modification with [3H] palmitoyl chloride in the reversed Aerosol OT micelles in octane were determined. The degree of enzyme modification depends on the molar ratio [palmitoyl chloride]/[protein]. The modification reaction is characterized by the wide pH-optimum range and proceeds with high speed. 相似文献
2.
Inhibitor-induced enzyme activation in organic solvents 总被引:8,自引:0,他引:8
The enzymatic activity of the protease subtilisin in anhydrous organic solvents can be dramatically increased by pretreating the enzyme before it is placed in the nonaqueous medium. For instance, lyophilization of subtilisin from aqueous solution containing competitive inhibitors (followed by their removal) created an enzyme which was up to 100 times more active than the enzyme lyophilized in the absence of such ligands. This phenomenon of ligand-induced "enzyme memory" also extends to the stability, affinity, and substrate specificity of subtilisin in organic solvents. 相似文献
3.
V P Torchilin A L Klibanov L Huang S O'Donnell N D Nossiff B A Khaw 《FASEB journal》1992,6(9):2716-2719
The less than optimal accumulation of immunoliposome-associated reagents at target sites has often been attributed to the rapid in vivo clearance of immunoliposomes from the blood. In an attempt to overcome the drawback of rapid clearance and use the targeting potential of immunoliposomes, we have prepared long-circulating, 111In-labeled immunoliposomes. Targeting properties and enhanced circulation times were demonstrated in a rabbit model of acute experimental myocardial infarct. The specificity of liposomes for newly exposed intracellular cardiac myosin at the necrotic sites was achieved by incorporating monoclonal antimyosin antibody. Extended circulation times were achieved by cocoating the antimyosin-liposomes with polyethylene glycol (PEG). The half-life of the immunoliposomes was 40 min, which increased to 200 min with 4% mol PEG and to approximately 1000 min with 10% mol PEG. The degree of binding of modified immunoliposomes at the target sites was also dependent on the concentration of PEG incorporated at the liposome surface. This study demonstrates the accumulation of long-circulating targeted liposomes at the area of acute rabbit experimental myocardial infarction. 相似文献
4.
The unbound bilirubin concentration and the enzymatic rate of bilirubin degradation by bilirubin oxidase in bilirubin-serum albumin solutions have been investigated experimentally and theoretically. A stoichiometric bilirubin-serum albumin binding analysis shows that the unbound bilirubin concentration depends only on the molar ratio of the total bilirubin concentration to the total serum albumin concentration. From the theoretical analysis and the measured unbound bilirubin concentrations, serum albumin may be modelled as a molecule having two binding sites, primary and secondary, with stoichiometric equilibrium constants of K(1) = 6 x 10(7)M(-1) and K(2) = 4.5 x 10(6)M(-1), respectively. The rate of total bilirubin degradation in bilirubin-serum albumin mixtures is zero order. An immobilized bilirubin oxidase reactor model, which shows good agreement with experimental bilirubin conversions, is presented. At a flow rate of 1 mL/min with a 8-mL reactor volume, a 50% bilirubin conversion per pass was observed with an inlet bilirubin concentration of 350muM and a serum albumin concentration of 500muM. 相似文献
5.
Evaluation of quantitative parameters of the interaction of antibody-bearing liposomes with target antigens 总被引:2,自引:0,他引:2
Alexander L. Klibanov Vladimir R. Muzykantov Nikolai N. Ivanov Vladimir P. Torchilin 《Analytical biochemistry》1985,150(2):251-257
The model system for the analysis of targeted liposomes is proposed--the layer of protein antigen adsorbed on polystyrene wells. Antibodies were treated with palmitoyl chloride and liposomes were produced by the cholate dialysis method in the presence of the modified protein (7 X 10(-4) mol protein/mol lipid). Affinity of antibody-bearing liposomes to the antigen on the surface of Multiwell plates was studied, and apparent dissociation constant value was estimated: KD was in the range 1.5 to 5 X 10(-9) M liposomes. Sequential transfers of liposomes in antigen-coated plates revealed that the high-affinity fraction of liposomes is adsorbed first. The bound fraction has 1.7-times-higher protein content. For effective in vivo targeting it would be necessary to have high-affinity liposomes and a high concentration of the target antigen. 相似文献
6.
V P Torchilin A L Klibanov N N Ivanov M A Gluckhova V E Koteliansky H K Kleinman G R Martin 《Journal of cellular biochemistry》1985,28(1):23-29
We have incorporated antibodies against fibronectin or laminin into liposomes and studied their interaction with insoluble forms of these antigens. The antibodies, after modification by palmitoylchloride, were incorporated into the lipid bilayer by the cholate dialysis method. The antibodies in the liposomes recognized their specific antigen with little reaction to the alternative attachment protein or to albumin (less than 2%). The binding of antibody-containing liposomes to insoluble antigen was inhibited by soluble antibodies to the respective antigens but not by antibodies to other antigens. The affinity constant of the liposome-antibody complex with the antigen was estimated at 1-10 X 10(-9) M liposomes. Thus, antibodies in liposomes retain their reactivity and specificity, and the reaction constant is comparable to that observed for immune complexes. 相似文献
7.
On the role of reversible denaturation (unfolding) in the irreversible thermal inactivation of enzymes 总被引:1,自引:0,他引:1
The contribution of the reversible thermal unfolding of an enzyme toward the overall irreversible thermoinactivation process has been examined both theoretically and experimentally. Using bovine pancreatic ribonuclease as a model, we have studied the effect of such variables as pH and salts both on the equilibrium constant of reversible denaturation and on the rate constant of the overall irreversible process. It has been demonstrated that at temperatures where a significant fraction of the enzyme molecules are in the native conformation, there is a correlation between the enzyme thermostabilities with respect to the reversible and irreversible inactivations: greater stability against the former is accompanied by greater stability against the latter. On the other hand, at very high temperatures (where essentially all of the enzyme molecules are unfolded), such a correlation does not exist. These findings are considered in terms of a kinetic model for irreversible enzyme thermoinactivation, and the implications of the derived relationship are discussed. 相似文献
8.
It has been found that sulfatase from Helix pomatia hydrolyzes beta-naphthyl sulfate much faster than alpha-naphthyl sulfate; e.g., at pH 7.8, while the former is readily hydrolyzed, the latter undergoes no appreciable hydrolysis. Kinetic investigations of both enzymatic and acid hydrolysis of naphthyl sulfates and their analogs indicate that in the enzymatic reaction the difference in reactivities is due to steric hindrances exerted in alpha-naphthyl sulfate by the benzene ring adjacent to the one bearing the sulfate group. (In the beta-ester this ring is remote from the site of hydrolysis.) The enzyme was immobilized and employed for the preparative resolution of alpha- and beta-naphthols: a mixture of the isomers was first sulfated with chlorosulfonic acid and then incubated with sulfatase covalently attached to alumina. The beta-naphthol produced was extracted with benzene, followed by acid hydrolysis of alpha-naphthyl sulfate in the remaining aqueous solution and extraction of the alpha-naphthol formed. Helix pomatia sulfatase also expresses a marked regiospecificity in the hydrolysis of ortho and para substituted phenyl sulfates. Therefore, the enzyme can be used for the preparative separation of naphthols as well as a variety of isomeric phenols. 相似文献
9.
Enzymatic catalysis in anhydrous organic solvents 总被引:28,自引:0,他引:28
A M Klibanov 《Trends in biochemical sciences》1989,14(4):141-144
Not only do enzymes work vigorously in anhydrous organic media, but in this unnatural milieu they acquire remarkable properties such as greatly enhanced stability, radically altered substrate and enantiomeric specificities, molecular memory, and the ability to catalyse unusual reactions. 相似文献
10.
The influence of the mode of enzyme preparation on enzymatic enantioselectivity in organic solvents and its temperature dependence 总被引:2,自引:0,他引:2
The enantioselectivities of subtilisin Carlsberg and Rhizomucor miehei lipase in organic solvents are found to strongly depend on the method by which the enzymes are prepared. For the transesterification between sec-phenethyl alcohol and vinyl butyrate in dioxane at 7 degrees C, the enantioselectivity of subtilisin precipitated with isopropanol is more than twice that of the enzyme prepared by lyophilization from aqueous buffer. Furthermore, the temperature dependence of the enantioselectivity is influenced by the mode of enzyme preparation. For example, in the aforementioned process the enantioselectivities of subtilisin lyophilized from aqueous buffer and crosslinked subtilisin crystals increase when the temperature is raised from 7 to 45 degrees C. In contrast, the enantioselectivities decrease with temperature for the enzyme precipitated from aqueous solution with acetone or isopropanol and for the enzymatic hydrolysis in water. The temperature dependence of the enantioselectivity of subtilisin lyophilized from buffer is markedly affected by the solvent: In acetonitrile and nitromethane the enzyme is more enantioselective at higher temperatures, while negligible temperature effects have been found in tetrahydrofuran and pyridine. Lyophilized lipase exhibits striking temperature dependencies of its enantioselectivity in dioxane, acetonitrile, and nitromethane, while showing almost none in pyridine, triethylamine, and tetrahydrofuran. The results underscore the importance of the mode of enzyme recovery on enantioselectivity and its temperature dependence in enzymatic reactions in organic solvents (in contrast to those in water). (c) 1996 John Wiley & Sons, Inc. 相似文献