Selma L. Bandemer

Structure of egg yolk very low density lipoprotein. Polydispersity of the very low density lipoprotein and the role of lipovitellenin in the structure

Abstract Egg yolk very low density lipoprotein contained on the average 75% of lipid which could be extracted by ether and 25% of a residual lipoprotein, the classical lipovitellenin. The ether-extracted lipid was composed of 75% triglycerides, 7% sterols, 2% mono- and diglycerides, and 16% phospholipids. Lipovitellenin contained 48% lipid composed of 87% phospholipids, 11% triglycerides, and 2% sterols. The protein vitellenin was composed for the most part of units of 74,000 and 270,000 daltons molecular weight. Egg yolk very low density lipoprotein is polydisperse. Preparative ultracentrifugation separated it into six fractions of different average molecular size, and gel chromatography separated it into five. The fractions of larger molecular size contained more lipid and triglyceride than did the fractions of smaller molecular size. The proteins of the fractions appeared to be similar. Egg yolk very low density lipoproteins appear to be a series of molecules composed of cores of lipid of varying sizes with each core surrounded by a layer of lipovitellenin, which is composed principally of glycoprotein and phospholipid.

Binding of lipid to protein in the low-density lipoprotein from the hen's egg

Abstract Low-density lipoprotein isolated from the yolk of hens eggs contained 86% lipid. Approx. 19% of the total lipids were extracted by diethyl ether from a solution of native low-density lipoprotein in 1.0 M NaCl solution. Treatment with urea, guanidine hydrochloride, sodium thioglycolate, or non-ionic detergents did not increase the amount of lipid extracted, but treatment with sodium dodecylsulfate or sodium deoxycholate increased lipid extracted by ether to 50–64%. Digestion of low-density lipoprotein with phospholipase C increased lipid extracted to 74%, but phospholipase D digestion had no effect. Ether extracted 98% of the lipid from trypsin-digested low-density lipoprotein, and this lipid was composed of 73% glycerides, 7% sterols, and 21% phosphatides compared to 36% glycerides, 9% sterols, and 52% phosphatides in the residue lipid. Trypsin released 84% of the protein as soluble peptides. Further digestion of the residue with papain released lipids and peptides, and digestion of that residue with pronase also released lipids and peptides. The residue left after pronase digestion contained 27% protein, 39% lipid, 1% carbohydrate, and 33% of unknown material. The data obtained support the view that the low-density lipoprotein is a sphere of lipid surrounded by a layer of protein and phospholipid with hydrophobic groups on the inside and hydrophylic groups oriented to the outside making it very soluble in water and insoluble in organic solvents.

Chromatographic determination of cysteic acid.

Abstract Difficulty was encountered in the determination of cysteic acid with ninhydrin after elution from a resin column, using a Time-Flow fraction-collector. Since the trouble arose from the variable pH obtained on the addition of sodium hydroxide to the eluate, a buffered solution of 2 N sodium hydroxide saturated with sodium citrate was used to produce the pH 5.0 required for maximum color development. The calibration for 10 ml of the tubes collecting the eluate, and the use of a standard cysteic acid curve facilitated the calculation of the cysteic acid concentration in the sample.

Heat inactivation of threonine, glycine, and the acidic amino acids.

Abstract Little or no destruction of threonine, glycine, aspartic acid, and glutamic acid occurred when soybean oil meal, soybean protein, or the protein plus sucrose, glucose, dextrin, agar-agar, gum arabic, or soybean oil was autoclaved for 4 hr. at 15 lb. pressure. A portion of each of these amino acids was “inactivated” or tied up in such a manner that the biologically active amino acid could be liberated by acid but not by in vitro trypsin and erepsin digestion. Studies with soybean protein and mixtures of soybean protein and other constituents of soybean oil meal indicated that two types of inactivation occurred during autoclaving. Protein-bound threonine, glycine, and glutamic acid reacted with sucrose or glucose (glycine to some extent with dextrin or agar-agar) to form a linkage resistant to enzymatic but not to acid digestion. Protein-bound aspartic and glutamic acids reacted with some other constituent of the protein to form a linkage resistant to trypsin and erepsin digestion in vitro but hydrolyzed by acid digestion. Part of the second carboxyl groups of protein-bound aspartic and glutamic acids are combined with ammonia as the amide and part are free. It was postulated that the free carboxyl groups react with the free amino groups of lysine and arginine and with the imidazolyl group of histidine to form a peptide-type linkage resistant to enzymatic cleavage.