Search PubMed⌕ Search

Biomedical subjects

R I Levy

Publications and source records attributed to R I Levy.

At least 127 records · Page 7Linked to original sources
PubMed1973

A comparaive study of the effects of chemical modification on the immunochemical and optical properties of human plasma low-density lipoprotein(s) and apoproteins.

1. The structure of human plasma low-density lipoprotein(s) [LD lipoprotein(s)] was investigated by several immunological and optical techniques. The effects of delipidation and of chemical modification by 3-carboxypropionylation, acetylation, diazotization and amidination were examined. A sensitive double-antibody radioimmunoassay for human LD lipoproteins is presented and is used to assess the extent of immunochemical modification. A computer best-fit analysis is used to analyse circular-dichorism (c.d.) spectra. These methods permit comparisons of the relative effects of chemical modification and delipidation of LD lipoprotein under similar experimental conditions. 2. 3-Carboxypropionylation, acetylation or diazotization produces qualitative and quantitative changes in the immunochemical properties of LD lipoprotein. Amidination causes minor changes detected by radioimmunoassay but not by double-diffusion experiments. In general, the order of effectiveness in displacing (125)I-labelled LD lipoprotein is amidinated>diazo or acetyl>3-carboxypropionyl derivatives. 3. The order of the extent of conformational alteration induced in apoLD lipoprotein and LD lipoprotein, as judged by c.d. analyses, was 3-carboxypropionylation>diazotization>acetylation or amidination. 4. Delipidation of LD lipoprotein results in immunological alterations that are qualitatively detected by antisera to LD lipoprotein. Four of five antisera to apoLD lipoprotein form precipitin lines of identity between native LD lipoprotein and apoLD lipoprotein in double-diffusion experiments. An anti-(apoLD lipoprotein) serum that forms precipitin lines of complete identity between LD lipoprotein and apoLD lipoprotein reacts differently with these two antigens in radioimmunoassay. ApoLD lipoprotein is only one-fourth to one-half as effective as LD lipoprotein, on a protein basis, in the displacement of (125)I-labelled LD lipoprotein from this anti-(apoLD lipoprotein). 5. Conformational analysis indicates that apoLD lipoprotein retains a high proportion of the structural integrity of the native lipoprotein. Delipidation induces a small decrease in the content of beta-structure and a small increase in disordered structure, without greatly affecting the alpha-helical content. Chemical modification produces more severe conformational changes of apoLD lipoprotein than of LD lipoprotein. Computer analysis of the c.d. spectra of apoLD lipoprotein indicates that addition of high concentrations of sodium decyl sulphate abolishes most of the beta-conformation concomitant with increases in alpha-helical and disordered structure. 6. There is parallelism between the alteration of the charge of LD lipoprotein and apoLD lipoprotein and the extent of immunochemical and conformational changes.

Acylation↗
PubMed1973

Biosynthesis of lymph and plasma lipoprotein apoproteins by isolated perfused rat liver and intestine.

The ability of rat intestine and liver to synthesize the various apoproteins of plasma lipoproteins was investigated. After the individual isolated organs were perfused with blood containing [(3)H]lysine, chylomicrons plus very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL) were isolated from the perfusates and the intestinal lymph. After lipoprotein delipidation, apoproteins were separated by polyacrylamide gel electrophoresis and the (3)H content was determined. Livers incorporated [(3)H]lysine into all apoprotein bands of VLDL and HDL. The (3)H content was greater in large proteins that remained in the stacking gel (group I, predominantly beta-apoprotein) than in proteins with apparent molecular weights near 50,000 (group II) or in the smaller peptides (molecular weights near 10,000, group III). In the intestine, (3)H was incorporated into group I and, in larger amounts, into group II apoproteins of lymph VLDL. No labeled VLDL appeared in the perfusate. (3)H was also incorporated into group II apoproteins of lymph and perfusate HDL. Significantly, no [(3)H]lysine was found in the group III peptides of any lymph or intestinal perfusate lipoproteins. Since these peptides were always present in VLDL from mesenteric lymph collected in vivo, the results suggest that nascent VLDL of gut origin acquires group III peptides from other lipoproteins that penetrate lymph from plasma.

Animals↗
PubMed1973

Metabolic fate of rat and human lipoprotein apoproteins in the rat.

The fate of (125)I-labeled apolipoproteins was studied in vivo in rats that had received intravenous injections of (125)I-labeled rat HDL and (125)I-labeled human HDL, LDL, and VLDL. Plasma decay curves of rat and human HDL were exponential with similar half-lives in the circulation (11-12 hr). After injection, low molecular weight apolipoproteins (apoLP-alanine of human HDL and fraction HS-3 of rat HDL) were found to redistribute to other lipoproteins, predominantly VLDL. Decay curves of individual HDL proteins were constructed after lipoprotein fractionation, delipidation, and polyacrylamide gel electrophoresis. It was found that the half-lives of the different HDL apoproteins were not identical. A major rat HDL protein (52% of total counts) had a circulating half-life (t((1/2))) of 12.5 hr. Two others had a t((1/2)) of 8-9 hr while the t((1/2)) of several others was 11-12 hr. The t((1/2)) of three well-characterized human HDL apoproteins, apoLP-glutamine I, apoLP-glutamine II, and apoLP-alanine, were 13.5, 9.0, and 15.0 hr, respectively. The fate of (125)I-labeled human VLDL and LDL apoproteins in rats was similar to that described previously in humans. After injection of (125)I-labeled human VLDL into rats, apoLP-glutamic acid and apoLP-alanine rapidly transferred to rat HDL and were lost thereafter from the circulation from both VLDL and HDL. The apoLDL moiety of human VLDL moved metabolically to the LDL density range (d = 1.019-1.063) through a lipoprotein of intermediate density (d = 1.006-1.019).

Alanine↗