37. NUCLEIC ACID AND PROTEIN SYNTHESIS 



357 



TABLE I 



A Summary of Some Physical Properties of Ribosomes 



a A. Tissues and J. D. Watson, Nature 182. 778 (1958). 



b W. C. Gillchriest and R. M. Bock, in "Microsomal Particles and Protein Synthesis" (R. B. Roberts, ed.), 

 p. 1. Pergamon Press, London, 1958. 



c F. C. Chao and H. K. Schachman, Arch. Biochem. Biophys. 61. 220 (1956). 



d P. O. P. Ts'o, J. Bonner, and J. Vinograd, Biochim. et Biophys. Ada 30, 570 (1958). 



e H. M. Dintzis, H. Borsook, and J. Vinograd in "Microsomal Particles and Protein Synthesis" (R. B. 

 Roberts, ed.), p. 95. Pergamon Press, London, 1958. 



/ M. L. Petermann, M. G. Hamilton, M. E. Balis, K. Samarth, and P. Pecora, in "Microsomal Particles 

 and Protein Synthesis" (R. B. Roberts, ed.), p. 70. Pergamon Press, London, 1958. 



et al. 16h ), and reticulocytes (cf. Dintzis et al. l6i ). Bacterial ribosomes are 

 discussed further in Chapter 38. 



To obtain mammalian ribosomes they must often be freed of the mem- 

 branous component of the microsomes either by treatment with deoxy- 

 cholate 35, 39, 47 or a high salt concentration. 35,48 Bacterial, yeast, and re- 

 ticulocyte particles may usually be obtained in relatively pure form directly 

 by breaking the cells and centrifuging. 



The secret of stabilization of ribosomes seems to lie chiefly in the level 

 of divalent metal ions, particularly Mg + +, in the medium. The pH of the 

 medium may also be important. 46 In the presence of adequate Mg ++ levels 

 it appears that the bulk of the ribosomes from all sources have a sedimen- 

 tation constant of about 70 to 80 aS, corresponding to a molecular weight of 

 3 to 4 X 10 6 . In this state they are quite stable. This uniformity extends 

 to the pattern of reversible disaggregation or dissociation which they un- 



47 M. L. Petermann and M. G. Hamilton, J . Biophys. Biochem. Cytol. 1, 469 (1955). 



48 J. L. Simkin and T. S. Work, Biochem. J. 65, 307 (1957). 



