Journal of Lipid Research, Vol. 8, 631-635, November 1967
Copyright © 1967 by Lipid Research, Inc.

Dissociation of low density lipoprotein-antibody precipitates at alkaline pH

Jiwhey Chung and Toshiro Nishida

The Burnsides Research Laboratory, University of Illinois, Urbana, Illinois 61801

The effect of alkaline pH on the dissociation of immunoprecipitates of low density lipoproteins (LDL) of the S_f 0-10 class was studied by immunological and ultracentrifugal methods. The precipitates prepared at the equivalence point were dissolved and centrifuged in sodium chloride solutions of density 1.063 and pH's between 10.25 and 11.5.

Analytical centrifugation of the top fraction, which floated at density 1.063, after dialysis against 0.9% sodium chloride of pH 7.4 revealed the presence of LDL and of soluble LDL-antibody complex. The amount of soluble complex was greater for the preparations obtained at lower pH than those obtained at higher pH and was undetectable at pH 11.5. The yield of immunoglobulin from the bottom fractions was maximal when the pH of the centrifugation medium was 11.0. Below pH 11.0, the greatly reduced yield of immunoglobulin was due partly to incomplete dissociation and partly to aggregation of soluble complex, while above pH 11.0 the decreased yield was possibly due to alkaline denaturation of the globulin. The immunoglobulin separated at pH 11.0 and dialyzed to pH 7.4 was reprecipitatable by LDL, and the reactivity did not seem to be appreciably influenced by the alkaline treatment.

Supplementary key words low density lipoproteins • anti-low density lipoproteins • immunoprecipitates • Solubilization • alkaline • analytical centrifugation • immunoglobulin • soluble complex

Submitted on May 8, 1967
Accepted on August 3, 1967

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