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I S O L a T I O N of S M O O T H V E S I C L E S a N D F R E E
| Content Provider | Semantic Scholar |
|---|---|
| Abstract | A B S T R A C T Microsomes, isolated from rat liver homogenate in 0.88 M sucrose, have been fractionated by differential centrifugation. The 2nd microsomal fraction, sedimented between 60 minutes at 105,000 g and 3 hours at 145,000 g, consists mainly of smooth vesicles, free ribosomes, and ferritin. By utilizing the differences in density existing between the membranes and the granular elements it has been possible to separate the smooth membranes from the free ribosomes and ferritin. The procedure is to resuspend the 2nd microsomal fraction in a sucrose solution of 1.21 or 1.25 density and centrifuge it at 145,000 g for 20 or 40 hours. A centripetal migration of membranes and a centrifugal sedimentation of granular elements are obtained. Phospholipids, as well as the enzymatic activities DPNH-cytochrome c reductase, glucose-6-phosphatase and esterase are localized in the membranes. The free ribosomes have been purified by washing. A concentration of 200 #g R N A per mg nitrogen has been reached. R N A is also present in the membranes. These results are discussed in relation to current views on microsomal structure and chemistry. It is well known that the microsomes, isolated by differential centrifugation, are rich in ribonucleic acid and phospholipids; biochemically this property serves to identify the microsomal fraction (1, 2). From a morphological point of view, the micro-somes are essentially composed of structures which arise through fragmentation of the endoplasmic reticulum existing in the cell in situ (1, 3). In rat liver mainly the following structures are found: "rough" vesicles characterized by dense particles, or ribosomes, attached to the outer surface of their membranes, "smooth" vesicles lacking ribosomes, free ribosomes, and ferritin (1-5). The importance of microsomes in cellular metabolism is known, particularly during the biosynthesis of proteins (6) and fatty acids (7, 8), and in the processes of detoxification (9-11); but although light is shed at times on the function of each microsomal structure, one aspect of the problem remains almost unknown: that of the physiological relationship between the different components. In order to approach this problem one indispensable step lies in the separation of the various structures composing the microsomes of rat liver, in defined fractions and in a pure and unaltered state. This consideration stems moreover from a more general approach which has asserted itself for several years and which attempts to correlate the biochemistry and morphology of the subcellular components (1, 2, … |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://jcb.rupress.org/content/jcb/12/1/17.full.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
