A Unique Ribonucleic Acid of Low Molecular Weight from Rat Liver Microsomes

Gardner, Jared; Hoagland, Mahlon B.

doi:10.1016/s0021-9258(18)99319-1

Cited by 26 publications

(2 citation statements)

References 28 publications

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“…Also, the small amount of RNA (Table I) seems to rule out significant contamination by rough-surfaced microsomes in the Golgi fraction . 4 It has been postulated that certain glycosyl transferases are localized in the Golgi apparatus and thus could serve as marker enzymes for this 4 The presence of RNA in different types of "smoothsurfaced membranes" is a matter of discussion, since theoretically it can be due either to ribosomes, subunits of ribosomes or to "membrane-constituents" (47)(48)(49) .…”

Section: Appearance Of Labeled Albumin In Subcellular Fractionsmentioning

confidence: 99%

Evidence for the Participation of the Golgi Apparatus in the Intracellular Transport of Nascent Albumin in the Liver Cell

Glaumann

Ericsson

1970

The Journal of Cell Biology

117

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A comparative biochemical and radioautographic in vivo study was performed to identify the site of synthesis and route of migration of albumin in the parenchymal liver cell after labeling with leucine-' 4 C or leucine-3 H via the portal vein. Free cytoplasmic ribosomes, membrane-bound ribosomes, rough-and smooth-surfaced microsomes, and Golgi membranes were isolated . The purity of the Golgi fraction was examined morphologically and biochemically. After administration of leucine-' 4C, labeled albumin was extracted, and the sequence of transport was followed from one fraction to the other . Approximately 2 min after the intravenous injection, bound ribosomes displayed a maximal rate of leucine-14C incorporation into albumin . 4 min later, a peak was reached for rough microsomes.Corresponding maximal activities for smooth microsomes were recorded at 15 min, and for the Golgi apparatus at -20 min . The relative amount of albumin, calculated on a membrane protein basis, was higher in the Golgi fraction than in the microsomes . By radioautography the silver grains were preferentially localized over the rough-surfaced endoplasmic reticulum at the 5 min interval . Apparent activity in the Golgi zone was noted 9 min after the injection ; at 15 and 20 min, the majority of the grains were found in this location. Many of the grains associated with the Golgi apparatus were located over Golgi vacuoles containing 300-800 A electron-opaque bodies . It is concluded that albumin is synthesized on bound ribosomes, subsequently is transferred to the cavities of rough-surfaced endoplasmic reticulum, and then undergoes migration to the smooth-surfaced endoplasmic reticulum and the Golgi apparatus . In the latter organelle, albumin can be expected to be segregated together with very low density lipoprotein in vacuoles known to move toward the sinusoidal portion of the cell and release their content to the blood .

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Section: Appearance Of Labeled Albumin In Subcellular Fractionsmentioning

confidence: 99%

Evidence for the Participation of the Golgi Apparatus in the Intracellular Transport of Nascent Albumin in the Liver Cell

Glaumann

Ericsson

1970

The Journal of Cell Biology

117

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“…3 . Smooth microsomes contain high G6Pase and IDPase activities, two enzymes which are re-2 The presence of RNA in smooth microsomal membranes is much debated, since it can be due to either ribosomes, subunits of ribosomes, or "membrane constituents" (25)(26)(27) . Smooth and rough microsomal subfractions were prepared on a CsCl-containing sucrose gradient (6, 9) .…”

Section: Chemical Compositionmentioning

confidence: 99%

Subfractionation of Smooth Microsomes From Rat Liver

Glaumann

Dallner

1970

The Journal of Cell Biology

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Total smooth microsomes from rat liver isolated on a Cs+-containing sucrose gradient were concentrated and subsequently fractionated by zone centrifugation on a stabilizing sucrose gradient. The prerequisite for fractionation is to prepare total smooth microsomes in a nonaggregated condition, as well as to utilize a procedure which counteracts enzyme inactivation . The median equilibrium density of the various smooth microsomal vesicles ranges from 1 .10 to 1 .18 . The phospholipid/protein ratio is identical in all subfractions, but cholesterol, on a PLP basis, is enriched in the subfractions with the highest sedimentation velocity . The enzyme distribution pattern reveals a pronounced heterogeneity. A number of NADH-and NADPH-oxidizing enzymes are concentrated in the upper part of the gradient and exhibit a certain degree of separation from G6Pase . Mg++-ATPase and AMPase are enriched in the lower part of the gradient . No specific enrichment of newly synthesized NADPH-cytochrome c reductase activity occurs in any of the subfractions after phenobarbital treatment . These data demonstrate that smooth microsomes, by adequate fractionation procedure, can be separated into subfractious of heterogeneous composition .

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