Nuclear Membrane Fractions Research Articles

The isolation of nuclear membrane from a large-scale preparation of bovine liver nuclei.

Abstract 1. 1. A procedure for the large-scale preparation of bovine liver nuclei is described. 2. 2. Nuclear membrane was prepared by treatment of nuclei with deoxyribonuclease followed by extraction with a 0.5 M MgCl2 solution. 3. 3. An evaluation of mitochondrial and microsomal contamination involving chemical, enzymatic and ultrastructural analysis indicated only slight contamination in both nuclear and nuclear membrane fractions. 4. 4. The total contaminating protein averaged 2.65% for nuclei and 10.6% for nuclear membrane. 5. 5. Electron microscopy showed that the membrane fraction contained both outer and inner nuclear membranes. 6. 6. The nuclear membrane fraction contained 74.6% protein, 8.9% RNA, 0.92% DNA, and 13.7% phospholipid. Recovery studies showed an average of 10.3% of the nuclear protein, 23.9% of the nuclear RNA, 0.27% of the nuclear DNA, and 47.1% of the nuclear phospholipid recovered in the membrane fraction.

Lipid composition of nuclear membranes isolated from bovine liver.

Abstract 1. 1. Nuclear membrane fractions were prepared from rat-liver nuclei by treatment with deoxyribonuclease and MgCl2. 2. 2. The lipid distribution and fatty acid composition of total lipids and individual phospholipids was determined. 3. 3. The ratio of protein to total lipid was 2.96. Phospholipids accounted for 62% of the total lipid fraction. The remainder was accounted for as neutral lipids. Non-phosphorus-containing polar lipids were not detected. Based on lipid phosphorus distribution the major phospholipids were phosphatidylcholine (55%), phosphatidylethanolamine (23%), phosphatidylinositol (8%), phosphatidylserine (6%) and sphingomyelin (6%). Cholesterol and free fatty acids were the major constituents of the neutral lipid fraction, accounting for t6 and t3%, respectively, of the total membrane lipids. 4. 4. Phosphatidylcholine was the least saturated and sphingomyelin the most saturated of the major phospholipids. Eighteen-carbon chain-length fatty acids accounted for 70% of the acyl residues of the total lipid fraction. The palmitic acid to oleic acid ratio of the total lipid fraction was 0.55.

Nuclear electron transport I electron transport enzymes in bovine liver nuclei and nuclear membrane

The electron transport enzymes NADH-cytochrome c reductase, NADH oxidase and cytochrome c oxidase are present in isolated bovine liver nuclei and highly concentrated in a nuclear membrane fraction. Evaluation of contamination indicates that the enzymes are of nuclear origin. Nuclear NADH oxidase is distinguished from mitochondrial NADH oxidase by the effects of exogenous cytochrome c, DNase and histone on enzyme activity. We suggest that the nuclear electron transport enzymes are located in the nuclear membrane.

Lipids of the BAI strain A avian tumor virus and of the myeloblast host cell

Lipids of the BAI strain A virus and of the myeloblast host cell and nuclear, microsomal and external membrane cell fractions were analyzed by thin-layer chromatography. Total virus lipids consisted of 34% cholesterol, 5.3% neutral fat and 61% phospholipid. Of the latter, the principal components were sphingomyelin, 16; phosphatidyl ethanolamine, 21; and lecithin, 11%, respectively. This constitution of the BAI strain A virus was proportionally similar to that of the influenza agent. Virus lipids were qualitatively similar to those of the whole host cell and the nuclear, microsomal, and cell membrane fractions. Marked quantitative differences were observed between the virus and host cell components, particularly with respect to the cell membrane fraction in which the low content of cholesterol, 9%, and 30% neutral fat were the reverse of the virus with 34 and 5.3% of these constituents. Major differences observed also with the phospholipids were, again, greater in the comparison between the virus and the cell membrane. The findings were interpreted to indicate the improbability of major cell membrane contribution to the virus lipids. Consideration of the analytical data and correlation with the ultrastructural aspects of BAI strain A budding from the myeloblast surface suggest that the virus lipids are specifically assembled in the process of virus synthesis not only from the external cell membrane but also principally from contiguous and possibly other cytoplasmic structures.

Polysomes on a nuclear membrane fraction as intermediates in the transfer of ribonucleic acid from the nucleus to the cytoplasm.

Polysomes on a Nuclear Membrane Fraction as Intermediates in the Transfer of Ribonucleic Acid from the Nucleus to the Cytoplasm