Nuclear Membranes From Mammalian Liver

Abstract

The qualitative and quantitative lipid composition of nuclei and nuclear membranes from pig and rat liver were determined . These determinations were compared with the corresponding data obtained for microsomes from the same material after similar treatments . The results indicate that, at least, by far the major part of the nuclear lipids is located in the membranes of the nuclear envelope . The phospholipid pattern of the nuclear membranes and the endoplasmic reticulum (ER) membranes in general is widely identical in both species . As a striking difference in the lipid composition, however, a fourfold increase of esterified cholesterol in the nuclear membranes was found . In a quantitative approach the ratio of total surface area of the nuclear lipids to the total surface area of the nuclear envelope membranes was calculated as being 3 .6, a value which fairly approximates the requirements of a bimolecular lipid leaflet model .

Effect of Plasma Membrane Lipid Composition on Cellular Susceptibility to Virus-induced Cell Fusion

“…The present results indicate, however, that the susceptibility of different cell types to virus-induced cell fusion is not simply related to the ratio of cholesterol to phospholipid in the plasma membrane of the cell. This is not surprising in view of the fact that mitochondrial membrane systems have a very low (< o'13) cholesterol to phospholipid ratio (Pascaud, Auliac & Pascaud, 1968;Suzuki, Mitropoulos & Myant, I969;Kleinig, I97O) yet rarely, if ever, fuse. Membranes of the lysosomal complex and endoplasmic reticulum are highly susceptible to fusion yet have significantly higher cholesterol to phospholipid ratios (Dingle, 1969;Renkonen et al 1972 ).…”

Cholesterol Metabolism in the Macrophage

“…Cytomembranes of the "thick" variety (80-100 A) which have potential access to the extracellular milieu are rich in cholesterol and include plasma membrane, lysosomal membrane, and secretion granules (1-10). In contrast, "thin" membranes (40-70 A) such as endoplasmic reticulum, mitochondria, and nuclear envelope are poor in cholesterol, whereas Golgi membranes are intermediate in size and cholesterol content (5,11,12).…”

“…Cytomembranes of the "thick" variety (80-100 A) which have potential access to the extracellular milieu are rich in cholesterol and include plasma membrane, lysosomal membrane, and secretion granules (1-10). In contrast, "thin" membranes (40-70 A) such as endoplasmic reticulum, mitochondria, and nuclear envelope are poor in cholesterol, whereas Golgi membranes are intermediate in size and cholesterol content (5,11,12).Although there is an extensive literature on cholesterol metabolism of the whole organism (13-16), our knowledge of the cellular level is fragmentary. Exceptions are the well-documented studies first described by Hagerman and Gould (17) demonstrating cholesterol exchange from plasma lipoproteins to the membrane of erythrocytes.…”

The Nuclear Envelope in Freeze-Etching

“…Peculiarities of the nuclear membrane enzymology have also been noted with the hen erythrocyte (Zentgraf et al, 1971). A certain distinctiveness of the nuclear membrane has also been noted at the membrane lipid level (e.g., Keenan et aI., 1970;Kleinig, 1970;Kleinig et al, 1971;Stadler and Kleinig, 1971). On the background of the membrane differentiation hypothesis as outlined by Grove et aI.…”

“…For this purpose, and in particular in order to examine the general architectural principles beyond the pecularities of one cell type, we chose the following widely divergent cellular systems: (a) Mature rat liver parenchyma, since this is a "reference" mammalian tissue cell which provides a good example of a differentiated steady-state cell system and in which a lot of work on the nuclear envelope structure, chemistry and function has already been done in many laboratories (see, e.g., Watson, 1959;Kashnig and Kasper, 1969;Zbarsky et al, 1969;Franke et aI., 1970;Kleinig, 1970;Franke et aI., 1971). (b) The hen erythrocyte as a cell system in an extreme "dead end differentiation" with an almost totally inactive nucleus.…”