Ts'o, Paul O. P. and Bonner, James and Vinograd, Jerome (1956) Microsomal nucleoprotein particles from pea seedlings. Journal of Biophysical and Biochemical Cytology, 2 (4). pp. 451-467. ISSN 0095-9901 http://resolver.caltech.edu/CaltechAUTHORS:TSOjcb56
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Ultracentrifugal analysis of an extract of pea epicotyls, previously freed of debris and larger particles by centrifugation at 40,000 g for 10 minutes, has revealed the presence of a major component which possesses a sedimentation coefficient of 74 S. This component constitutes about 25 per cent of the TCA-precipitable material in the clarified epicotyl extract and is estimated to make up 1 to 2 per cent of the dry weight of the original tissue. In size, chemical composition, and morphology, the 74 S component resembles the nucleoproteins of the microsomes from animal tissues. The 74 S component of pea epicotyl extracts has been purified by repeated cycles of differential centrifugation to yield a preparation which is 80 per cent homogeneous in the analytical ultracentrifuge. It has been found to contain 30 to 37 per cent RNA as judged by a variety of analytical techniques. Approximately 55 per cent of the weight of the material is protein and a further 4.5 per cent phospholipide. Electron micrographs of air-dried specimens of the purified preparation show the 74 S constituent to be flattened spheres with an average height of 180 A and an average diameter of approximately 280 A. The molecular weight of the 74 S particles is computed from sedimentation, viscosity, and partial specific volume data to be 4.5 million ± 10 per cent in agreement with the value estimated from electron micrographs. The 74 S or microsomal component of pea epicotyls is rapidly aggregated in the presence of low concentrations of Mg ions or by somewhat higher concentrations of Ca or K salts. ATP on the contrary causes resolution of electrolyte-induced microsomal aggregates with simultaneous degradation of the particles to an ultracentrifugally inhomogeneous mixture of lower molecular weight materials.
|Additional Information:||Copyright © 1956 by Rockefeller University Press (Received for publication, April 25, 1956) Report of work supported in part by a grant No. H-1645 from the National Institutes of Health, United States Public Health Service. Contribution No. 2092 from the Gates and Crellin Laboratories of Chemistry, California Institute of Technology, Pasadena.|
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|Deposited On:||13 Sep 2006|
|Last Modified:||26 Dec 2012 09:02|
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