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Physiochemical properties of rat liver mitochondrial ribosomes

By Vinood B. Patel, Carol C. Cunningham and Roy Hantgan

Abstract

In the present study, the physiochemical properties of\ud rat liver mitochondrial ribosomes were examined and\ud compared with Escherichia coli ribosomes. The sedimentation\ud and translational diffusion coefficients as\ud well as the molecular weight and buoyant density of rat\ud mitochondrial ribosomes were determined. Sedimentation\ud coefficients were established using the time-derivative\ud algorithm (Philo, J. S. (2000) Anal. Biochem. 279,\ud 151-163). The sedimentation coefficients of the intact\ud monosome, large subunit, and small subunit were 55, 39,\ud and 28 S, respectively. Mitochondrial ribosomes had a\ud particle composition of 75% protein and 25% RNA. The\ud partial specific volume was 0.688 ml/g, as determined\ud from the protein and RNA composition. The buoyant\ud density of formaldehyde-fixed ribosomes in cesium chloride\ud was 1.41 g/cm3. The molecular masses of mitochondrial\ud and E. coli ribosomes determined by static lightscattering\ud experiments were 3.57 +/- 0.14 MDa and 2.49 +/-\ud 0.06 MDa, respectively. The diffusion coefficient obtained\ud from dynamic light-scattering measurements\ud was 1.10 +/- 0.01 x 10 -7 cm2 s-1 for mitochondrial ribosomes and 1.72 +/- 0.03 x 10 -7 cm2 s-1 for the 70 S E. coli monosome. The hydration factor determined from these\ud hydrodynamic parameters were 4.6 g of water/g of ribosome\ud and 1.3 g/g for mitochondrial and E. coli ribosomes,\ud respectively. A calculated hydration factor of 3.3 g/g for\ud mitochondrial ribosomes was also obtained utilizing a\ud calculated molecular mass and the Svedberg equation.\ud These measurements of solvation suggest that ribosomes\ud are highly hydrated structures. They are also in\ud agreement with current models depicting ribosomes as\ud porous structures containing numerous gaps and tunnels.\u

Topics: UOW2
OAI identifier: oai:westminsterresearch.wmin.ac.uk:414
Provided by: WestminsterResearch

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