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W Känzig

Publications and source records attributed to W Känzig.

10 recordsLinked to original sources
PubMed1985

Temperature dependence of fibrin polymerization: a light scattering study.

The aggregation of fibrin occurring in a fibrinogen solution upon addition of the enzyme thrombin has been studied prior to the sol-gel transition at different temperatures by means of dynamic light scattering and simultaneous measurement of the released fibrinopeptide A (FPA). The evolution of the polymer distribution with time was found to be independent of the temperature. The analysis of the experiments yields the explanation: with increasing temperature the rate of FPA release increases because it involves an activation energy, whereas the aggregation rate of the fibrin monomers decreases because it is exothermic. The light scattering experiments show that the state of aggregation is a chemical equilibrium that can be shifted by the addition of the tetrapeptide Gly-Pro-Arg-Pro. From dynamic light scattering data it is possible to derive the probability of bond formation between fibrin molecules and from it the aggregation enthalpy. For 30 degrees C a value of -19 kcal/mol was obtained.

Fibrin↗
PubMed1984

Preparation of monodisperse vesicles with variable size by dilution of mixed micellar solutions of bile salt and phosphatidylcholine.

We have investigated by means of quasi-elastic light scattering the aggregative behavior of aqueous mixed micellar solutions of glycocholate and phosphatidylcholine. Upon dilution with buffer the micellar size and the polydispersity increases dramatically, and, as the system is diluted beyond the mixed micellar phase boundary, a spontaneous transition from polydisperse micelles to monodisperse vesicles occurs. The radius of the vesicles formed upon dilution depends strongly upon the final composition of the solution and can be varied between 120 and 550 A. In contrast to the thermodynamically stable mixed micelles these vesicle solutions can be brought into a metastable state in which it is possible to remove by dialysis the bile salt molecules from the mixed vesicles without changing their radius by more then 10%. The combination of dilution and dialysis thus represents a method for the preparation of unilamellar, monodisperse and detergent-free vesicles with a desired radius that can be chosen between 120 and 500 A.

Bile Acids and Salts↗
PubMed1984

Quasi-elastic light scattering studies of native hepatic bile from the dog: comparison with aggregative behavior of model biliary lipid systems.

Using quasi-elastic light scattering ( QLS ), we have characterized the macromolecular components in hepatic bile obtained from the dog and compared these results with data from model bile solutions containing the bile salt (BS) sodium taurocholate (TC), egg lecithin (L), and cholesterol (Ch). Native bile samples were obtained by direct catheterization of the common bile duct in a previously cholecystectomized dog fitted with a Thomas duodenal cannula. Hepatic bile was sampled during three secretory states: (A) unstimulated "fasting" bile, (B) "stimulated" secretion during an intravenous TC infusion, and (C) "secretin-stimulated" secretion. All three samples had comparable molar ratios of L/BS (0.21 +/- 0.03) and Ch/L (0.027 +/- 0.006) but differed in the total lipid concentration (BS + L + Ch): (A) 13.1 +/- 0.8, (B) 6.7 +/- 0.8, and (C) 3.0 +/- 0.4 g/dL. From the QLS autocorrelation functions measured on samples B and C, three macromolecular components (denoted 1 alpha, 1 beta, and 2) were resolved. Component 1 alpha (hydrodynamic radius R1 alpha = 10 +/- 2 A) is comparable in size to the micellar aggregates of model systems. Component 1 beta (R1 beta = 67 +/- 7 A) appears to reflect an average of biliary proteins. Component 2 (R2 = 650 +/- 15 A) is a trace component whose size and sedimentation behavior are compatible with those of the canalicular membrane vesicles postulated to be present in bile [ Godfrey , P. P., Warner, M. J., & Coleman , R. (1981) Biochem. J. 196, 11]. Serial dilution of the B and C bile samples with Tris buffer (0.15 M NaCl, pH 8.0) showed a remarkable similarity in the behavior of the 1 alpha component as compared to the mean hydrodynamic radius Rh of similarly diluted model bile solutions. When a critical dilution factor, d gamma, is reached, Rh increases abruptly from approximately 30 to approximately 400 A. Above a second dilution factor, d alpha, it then decreases to a value of approximately 150 A. Similar results were obtained on sample A but were shifted to higher dilutions. Such behavior is consistent with the presence of "mixed disk" micelles [ Mazer , N. A., Benedek , G. B., & Carey, M. C. (1980) Biochemistry 19, 601] in native bile which undergo a micelle-to-vesicle transition upon dilution. From the d gamma and d alpha values, estimates of the intermicellar bile salt concentrations were made for all three samples (range 1.4-6.2 mM) which agree well with previous experimental results on model and native bile. These studies offer compelling evidence for the existence of micellar aggregates in native bile whose size, structure, and equilibria are similar to those found in model bile solutions.

Animals↗
PubMed1982

Fibrin aggregation before sol-gel transition.

Fibrinogen solutions (concentrations 2 mg/ml, 0.15-M Tris-NaCl buffer, pH 7.4) were incubated at 20 degrees C with quantities of reptilase or thrombin that were so small that the polymerization process could be followed for several hours by means of static and dynamic light scattering. The scattered intensity and its correlation function were recorded at scattering angles between 30 degrees and 150 degrees. The measured data were compared with model calculations based on the Flory-Stockmayer distribution, which predicts a sol-gel phase transition. This distribution is characterized by a parameter, lambda, that indicates the extent of aggregation. lambda = 0 corresponds to the monomeric solution, and lambda = 1 indicates the sol-gel transition. Good agreement was found for monomeric units of 75-nm length aggregating (a) end-to-end in the early stage (0 less than or equal to lambda less than or equal to 0.3), and (b) in a staggered overlap pattern for the progressing polymerization (0.3 less than or equal to lambda less than 1). Before the gel point was reached, no systemic difference was observed between the data obtained after activation with thrombin which releases both fibrinopeptides A and B from fibrinogen, and reptilase, which exclusively releases the fibrinopeptides A. This confirms that the release of the fibrinopeptides A is the essential prerequisite for the aggregation process.

Batroxobin↗
PubMedDate not supplied

Dynamic laser light scattering studies of the micelle to vesicle transition in model and native bile.

Using quasielastic light scattering, we investigated the formation of vesicles produced spontaneously by diluting a mixed micellar solution of bile salt and lecithin beyond the micellar phase boundary. The vesicles were nearly monodisperse, and their size varied between 120 to 500 A depending upon the dilution conditions. A systematic study of the dependence of the vesicle size upon the bile salt and lecithin concentration was made and interpreted in terms of a simple equilibrium model. Likewise, the particle size distribution in native bile obtained from the dog was studied. A comparison of the dilution effect on native bile and on model bile of identical biliary lipid composition provides unambiguous evidence for micellar aggregates and the occurrence of a micelle to vesicle transition in native bile.

Animals↗