Search PubMed⌕ Search

Biomedical subjects

R Nilsson

Publications and source records attributed to R Nilsson.

At least 145 records · Page 8Linked to original sources
PubMed1968

Heterogeneity of rough-surfaced liver microsomal membranes of adult, phenobarbital-treated, and newborn rats.

Rough microsomes from the livers of adult, phenobarbital-treated, and newborn rats were subfractionated on a continuous sucrose gradient. Among the subfractions a marked heterogeneity in the distribution patterns of some enzyme activities appears. The isopycnic density of the various fractions in aqueous sucrose ranges from 1.17 to 1.25. The sedimentation coefficients (s(0)) in 0.25 M sucrose lie between 0.4 x 10(3) S and 1.2 x 10(3) S. In adult animals, the NADH- and NADPH-cytochrome c reductase as well as the G6Pase activities are much higher in the slower sedimenting fractions than in the pellet. The increase in the level of G6Pase induced by fasting as well as the phenobarbital-induced changes are most prominent in the slowly sedimenting fractions. Three injections of phenobarbital have no effect on the specific NADPH-cytochrome c reductase activity in the pellet, but cause a significant increase of this enzyme activity in the light fractions. In the newborn animal, the NADH-ferricyanide reductase and NADPH-cytochrome c reductase activities are highest in the light fractions. On the other hand, the amount of cytochrome b(5) is evenly distributed in all cases. Short-term incorporation of leucine-(14)C and glycerol-(3)H in vivo after phenobarbital treatment shows contrasting results, as the former is increased and the latter is decreased in the slowly sedimenting fractions. Leucine-(14)C incorporation into isolated, total membrane proteins is greater in both phenobarbital-treated and newborn animals than in untreated adults. The data support a multistep model for membrane biogenesis and indicate dynamic and individual behavior of the different parts of the rough-surfaced endoplasmic reticulum.

Aging↗
PubMed1966

Mechanism of the cation effect in subfractionation of microsomes.

It was previously found that cations introduced into a discontinuous sucrose gradient exert a very pronounced effect on microsomal vesicles, and this principle proved to be effective in microsomal subfractionation. The mechanism of the cation effect was investigated. By using the radioactive isotopes (137)Cs and (85)Sr, it could be calculated that the amount of ions bound to the various subfractions increases their density by 0.14%, thereby enhancing the sedimentation velocity by only approximately 7%. In the presence of Cs(+) the total volume of the microsomal pellet was decreased by approximately 15%. Assuming this change in volume to be due to a contraction of the individual vesicles, a roughly 2(1/2)-fold increase in sedimentation velocity would be expected. It is further demonstrated, on the basis of light scattering and millipore filtration experiments, that monovalent cations cause an extensive aggregation of rough microsomes and a less pronounced aggregation of smooth microsomes. The mean radius of the sedimenting particles of rough microsomes was found to be at least doubled or trebled in the presence of Cs(+), which would give a 4- to 9-fold increase in the sedimentation velocity. Aggregation, therefore, appears to be the main factor in the accelerated sedimentation of rough microsomes in the presence of CsCl. Divalent cations exert a similar effect on a subfraction of the smooth microsomes. Isolated smooth microsomes are very unstable and often exhibit spontaneous aggregation. The presence of attached ribosomes, however, appears to impart greater stability to the rough microsomes as well as increasing their ability to bind monovalent cations. The primary cause of the aggregation of microsomal vesicles is probably due to a change in net charge.

Adenosine Triphosphatases↗