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Biomedical subjects

M C Ritter

Publications and source records attributed to M C Ritter.

29 records · Page 2Linked to original sources
PubMed1981

Stimulation of glycolipid synthesis and exchange by human serum high density lipoprotein-3 in human fibroblasts and leukocytes.

Upon exposure to either human skin fibroblasts or human circulating leukocytes, the composition of human serum high density lipoprotein-3 (HDL3) was modified by the apparent loss of apolipoprotein A-II and a 2- to 4-fold increase in glycosphingolipid content. Exposure of HDL3 to leukocytes produced an increase in the content of lactosylceramide, which is the major glycolipid in leukocytes, whereas exposure of HDL3 to human skin fibroblasts produced predominantly an increase in trihexosylceramide, which is the major glycolipid in fibroblasts. Other protein components of HDL3 (such as apolipoprotein A-I) were unaffected and there were no major changes in either neutral lipid or phospholipid composition. The increase in glycosphingolipid content of both cells and reisolated HDL3 particles was HDL3 concentration-dependent up to a concentration of 1 mg/ml and appeared to be the result of a stimulation of cellular glycolipid synthesis by HDL3 and subsequent transfer to HDL3 in the medium. A similar stimulation could not be produced by either low density lipoprotein or lipoprotein-deficient human serum. The coaddition of HDL3 and lipoprotein-deficient serum reduced both the loss of apolipoprotein A-II and the change in HDL3 glycolipid content, but not the increase in cellular glycolipid content, suggesting that modification of the apolipoprotein A-II peptide may enhance the ability of HDL3 to acquire new glycolipid from cells.

Cells, Cultured↗
PubMed1977

Role of apolipoprotein A-I in the structure of human serum high density lipoproteins. Reconstitution studies.

For a better definition of the role of human serum apolipoprotein A-I (apo A-I) in high density lipoprotein structure, a systematic investigation was carried out on factors influencing the in vitro association of this apoprotein with lipids obtained from the parent high density lipoprotein (HDL); these lipids include phospholipids, free cholesterol, cholesteryl esters, and triglycerides. Following equilibration, mixtures of apo A-I and lipids in varying stoichiometric amounts were fractionated by sequential flotation, CsCl density gradient ultracentrifugation, or gel-permeation chromatography, and the isolated complexes were characterized by physicochemical means. As defined by operational criteria (flotation at density 1,063 to 1.21 g/ml), only two types of HDL complexes were reassembled; one, reconstituted HDLS, small with a radius of 31 A, and the other, reconstituted HDLL, large with a radius of 39 A. The two types incorporated all of the lipid constituents of native HDL and contained 2 and 3 mol of apo A-I, respectively. A maximal yield of reconstituted HDL (R-HDL) was observed at an initial protein concentration of 0.1 muM, where apo A-I is predominantly monomeric. At increasing protein concentrations, the amount of apo A-I recovered in R-HDL was found to be proportional to the initial concentration of monomer and dimer in solution. The composition and yield of the complexes were independent of ionic strength and pH within the ranges studied. Both simple incubation and cosonication of apo A-I with HDL phospholipids produced complexes of identical composition, although the yeild of complexes was higher with co-sonication. When the comparison of the same methods was extended to mixtures of apo A-I and whole HDL lipids, the results confirmed previous observations that co-sonication is essential for the incorporation of the neutral lipid into the R-HDL complexes. The results indicate that (a) in vitro complexation of apo A-I with lipids is under kinetic control; (b) apo A-I can generate a lipid-protein complex with properties similar to those of the parent lipoprotein; (c) the process requires well defined experimental conditions and, most importantly, the presence in solution of monomers and dimers of apo A-I; (d) the number of apo A-I molecules incorporated into R-HDL determines the size and structure of the reassembled particle. All of these observations strongly support the essential role of apo A-I in the structure of human HDL.

Amino Acids↗
PubMed1973

Squalene and sterol carrier protein: structural properties, lipid-binding, and function in cholesterol biosynthesis.

Squalene and sterol carrier protein of liver plays a general role as a vehicle for cholesterol and its water-insoluble precursors; the carrier protein is essential for enzymic cholesterol synthesis. Liver microsomal enzymes contain a small amount of endogenous carrier protein, which is readily removed by washing or purification of the enzyme. Enzymic conversion to products of a cholesterol precursor.carrier protein complex is markedly faster than that for initially unbound sterol. The protomer form of the carrier protein has a molecular weight of 16,000; during sodium dodecyl sulfate gel electrophoresis one band is observed. Phospholipid facilitates the aggregation of the protomer to the oligomer form (>150,000 daltons; purified 720-fold) accompanied by the binding of cholesterol precursors to the oligomer. The carrier protein binds fatty acids as well as cholesterol precursors, suggesting that it may more generally be a lipid carrier protein with "squalene and sterol carrier protein" describing the functional aspects of the lipid carrier in cholesterol biosynthesis. Studies with several steroids and related compounds revealed that the binding sites of lipid carrier protein must contain highly specific hydrophobic and polar regions.

Animals↗