Permeability of Microsomal Membranes Isolated From Rat Liver

Abstract

Water compartments, permeability, and the possible active translocation of various substances in rat liver microsomes were studied by using radioactive compounds and ultracentrifugation. The total water of the microsomal pellet, 3.4 #l/rag dry weight, is the sum of water in the extramicrosomal and intramicrosomal spaces, or 56 and 44%, respectively. Sucrose space accounts for 77% of the intramicrosomal water and the hydration water ~ 14 %, leaving almost no sucrose-impermeable space when using the ultracentrifugation approach. With increasing sucrose concentration, microsomes do not show an osmotic response. The intramicrosomal water decreases greatly-in the presence of Cs + and Mg ++ in rough but not in smooth microsomes. Uncharged substances of molecular weight of up to at least 600 freely penetrate microsomal membranes, which already become impermeable to charged substances at a molecular weight of 90. These substances also induce an osmotic response. The vesicles can be made permeable to charged substances after water treatment and cooling, which, however, does not increase glucose-6-phosphatase and inosine diphosphatase (IDPase) activities, and these enzymes can still be activated by deoxycholate. IDPase, reduced nicotinamide adenine dinucleotide-cytochrome c reductase, and reduced nicotinamide adenine dinucleotide phosphate-dependent hydroxylation reactions, performed in vitro, also disproved the hypothesis of an accumulation of charged substances inside of vesicles of being a major pathway. The products of the enzymic reactions as well as the glucuronidated form of a hydroxylated product can be recovered on the cytoplasmic side of membranes, and little accumulation occurs in the intravesicular compartment.

Analytical Study of Microsomes and Isolated Subcellular Membranes From Rat Liver

“…As illustrated in Fig. 8, the relationship between particle density and density of the sucrose solution approaches linearity for several constituents, as is to be expected on theoretical grounds (10,16,20) for particles permeable to sucrose, as microsomes have been reported to be (29 (11), and 5Cnucleotidase (.) as a function of the density of the sucrose solution in which they were suspended.…”

Evaluation of data in terms of two-dimensional random walk model: Interaction between NADH-cytochrome b5 reductase and cytochrome b5

“…Preparation of wrongside-out microsomal vesicles are not available. Microsomal vesicles have been useful for studies of the transverse asymmetry of proteins, because they appear to mirror the properties of the endoplasmic reticulum (11). It is now well established that the functional asymmetry of many biological membranes is directly related to the absolute asymmetric distribution of proteins transversely across the membrane.…”

Carrier-mediated translocation of uridine diphosphate glucose into the lumen of endoplasmic reticulum-derived vesicles from rat liver.

“…Uptake of radiolabeled nucleotide or sucrose into microsomes was determined by a rapid filtration technique (16,17) using mixed cellulose filters (type HAWP 02500, 0.45 Mum pore size, from Millipore Corp., Bedford, MA) and an ultrafiltration manifold (FH 225V; Hoefer Scientific Instruments, San Francisco, CA). Microsomes (10 mg protein/ml except when stated otherwise) were resuspended in argon-flushed ice-cold 0.25 M sucrose containing 10 mM NaF and buffered to pH 7.4 with 10 mM Hepes (buffer B).…”