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Biomedical subjects

M Fisch

Publications and source records attributed to M Fisch.

At least 91 records · Page 5Linked to original sources
PubMed1988

Quasi-elastic light scattering of antigen-antibody complexes.

Many biological properties of immune complexes (IC) depend upon their size. Quasi-elastic light scattering (QLS) was used to measure a mean equivalent hydrodynamic radius (Rh) and variance of the distribution of model IC composed of bovine serum albumin (BSA) as antigen (Ag) and combinations of two or three well-characterized monoclonal antibodies (MAb) which bound noncompetitively to unique epitopes on BSA. With the molar ratio (X) of each MAb to Ag fixed, Rh increased with concn. Rh was maximal at equivalence (X = 0.5) with two MAb and at slight MAb excess (X = 0.67) with three MAb. The largest Rh with two MAb was about 200 A, and Rh was uniformly different amongst the three combinations of two MAb IC. The largest hydrodynamic radius of individual complexes which formed with two MAb was estimated to be about 400 A; even larger individual complexes were formed with three MAb. Size changes following alteration of solution concns were also followed with QLS. Kinetics of two MAb IC association were too fast to observe; dissociation following large dilution (40-fold) required 5-10 min to attain a new steady state, much less at small dilution. With three MAb, Rh dropped sharply in 5 min and became steady after 1-2 hr. These results suggest that conventional chromatographic and ultracentrifugation techniques for studying IC size, involving large dilution and long measurement time, provide misleading results. Association of three MAb produced a rapid initial increase of Rh in several min, followed by diverse behavior which depended upon concn. From high to low concn, these included (1) exponential growth of Rh with time and appearance of visible macroscopic particles; (2) metastable states for several hr followed by slow growth to large size over several days, leading to formation of particles; and (3) rapid growth to steady state conditions with no visible particles. This heretofore unobserved equilibrium and kinetic behavior of model IC in solution may be reflected in the behavior of more complex, naturally occurring IC.

Animals↗
PubMed1985

Solution studies of the quaternary structure and assembly of human von Willebrand factor.

The reversible association of protomers of von Willebrand protein (vWF) was studied in order to analyze the forces and mechanism of vWF polymer assembly. At concentrations of vWF found in plasma (approximately 16 micrograms/mL), disulfide bond reduction with 50 mM 2-mercaptoethanol (2-ME) markedly reduced both vWF activity, as measured by ristocetin-dependent platelet agglutination, and average polymer size (Rh, the mean hydrodynamic radius) in solution, as determined by quasi-elastic light scattering (QLS) and by gel filtration chromatography. With increasing vWF concentration, activity and Rh increased despite reduction of interprotomer disulfide bonds. Changes in temperature after 2-ME treatment produced reversible changes in activity and Rh. Varying the total vWF concentration at any given temperature after 2-ME treatment changed Rh in a consistent and predictable fashion, so that estimates of the dissociation constant for vWF protomer-polymer equilibrium were obtained: Kd5 degrees C = 0.77 micrograms/mL, Kd25 degrees C = 2.4 micrograms/mL, and Kd37 degrees C = 7.7 micrograms/mL, where under the conditions of reduction presented here, the basic protomer of vWF is a dimer. Increasing ionic strength after 2-ME treatment with 1 M KCl did not change Rh, while approximately 100 microM sodium dodecyl sulfate (SDS) or approximately 300 microM sodium deoxycholate (DOC) reduced both Rh and activity compared with those of unreduced polymer. These data show that disulfide bonds are necessary to maintain vWF polymer size and activity at plasma concentrations but that noncovalent forces of association can maintain vWF polymer size and activity at higher concentrations. These forces of association may be important for polymer assembly during intracellular synthesis of vWF.

Disulfides↗