|Effect of pressure and ionic strength on the self-association of Apo-A-I from the human high density lipoprotein complex. |
Formisano, S, et al.
J. Biol. Chem., 253: 354-9 (1978)
The self-association of apo-A-I isolated from the human high density lipoprotein complex has been investigated by gel permeation chromatography and sedimentation equilibrium. The apparent weight average molecular weight (MWapp) versus Apo-A-I concentration profile was found to be sensitive to ionic strength and pressure; MWapp increased with increasing ionic strength and decreasing rotor speed. The data were consistent with a monomer-dimer-tetrameroctamer association shceme over all conditions investigated if a change in the partial specific volume of apo-A-I upon association of 5.5 x 10(-2) ml/g is postulated.
|Apolipoprotein A-II content of human plasma high density lipoproteins measured by radioimmunoassay. |
Schonfeld, G, et al.
J. Lipid Res., 18: 645-55 (1977)
A double antibody radioimmunoassay for human ApoA-II is reported. ApoA-II isolated from human plasma high density lipoprotein (HDL) by column chromatography migrated as a single band on polyacrylamide disc gel electrophoresis, had the appropriate amino acid composition, and provoked the production of monospecific antisera. (125)I-ApoA-II (iodinated by lactoperoxidase, purified by Sephadex G-75 chromatography) migrated with "cold" ApoA-II as a single band on disc gel electrophoresis in SDS. Its specific radioactivity was 5-12 mCi/ micro g. In assays, (0.05 M barbital buffer, 0.01% Triton X-100, pH 8.6) over 90% of (125)I-ApoA-II was bound by excess first antibody and over 95% was displaced by excess "cold" ApoA-II. Low density lipoprotein, very low density lipoprotein, ApoA-I, ApoC-II, and ApoC-III displaced no counts. Intraassay and interassay coefficients of variation for lipoprotein or plasma samples were 7 +/- 4 and 11 +/- 6%, respectively. As little as 1.0 ng of ApoA-II was detectable with a precision of 10%. ApoA-II made up 20-25% of the proteins of HDL (d 1.083-1.19), HDL(2) (d 1.083-1.124), and HDL(3) (d 1.124-1.19) on column chromatography. The ApoA-II contents of these HDL fractions were also 20-25% by radioimmunoassay. Similar results were obtained whether assays were carried out on intact or delipidated HDL samples. Thus, in contrast with ApoA-I (only 10% of which is detectable), all of the ApoA-II contents of intact HDL are detected with accuracy by this assay. Plasma levels of ApoA-II in young normolipemic subjects were approximately 40 mg/dl (n = 29). In these subjects, over 98% of ApoA-II was found in the d 1.063-1.21 density fractions.