356 MAHLON B. HOAGLAND 



It is important to note, however, that the ribosomes do not have a con- 

 tinuous size distribution, but rather show a tendency to appear in groups 

 of sizes having sedimentation constants around 80, 40, 20 S, and small 

 amounts of even more slowly sediment ing material. Thus Petermann et al. 

 found the relative proportion of smaller particles increased in regenerating 

 as opposed to normal rat liver, 42 in leukemic mouse spleen as opposed to 

 normal, 42 and in rat liver hepatomas and cholangiomas versus normal. 34 In 

 ascites tumor cells, Littlefield et al. 30 found that the particles obtained were 

 of relatively low average sedimentation constants, 20 and 27»S. Schachman 

 et a/. 43 found a wide range of particle sizes in yeast and bacterial cells. Ashi- 

 kawa 16c has demonstrated striking changes in the sedimentation patterns 

 of yeast particles in the transition from dormancy to rapid growth; resting 

 cells have a preponderance of 80 S particles which disappear and are re- 

 placed by more slowly sedimenting particles as the cells enter the log phase 

 of growth. 



Petermann suggested early that the smaller ribosomes, and those not 

 attached to membranes, are perhaps concerned with the synthesis of the 

 cell's own protein substance, the larger ones with the synthesis of export- 

 able protein products of the differentiated cell. As we shall see in the follow- 

 ing section, however, the bulk of ribosomes, when isolated from tissues and 

 stabilized by Mg ++ , are remarkably uniform in size. Intracellularly, the 

 particles appear as relatively uniform bodies, also in electron micrographs. 

 One may well ask whether the above-mentioned variety of sizes found in 

 tissues is an indication of the true state of the ribosomes in nature or of a 

 differing lability to isolation procedures. It would seem probable that many 

 of the findings could be explained by dissociation of particles during isola- 

 tion. Such altered stability of particles reflecting differences in protein syn- 

 thetic activity of tissues is of considerable interest, but its meaning is un- 

 known as yet. 



The uniformity of ribosomes from a wide range of cell types is illustrated 

 in Table I. Ribosomes have now been isolated — and their physical prop- 

 erties studied — from such sources as Escherichia coli u (cf. also Roberts et 

 a/., 16d Dagley and Sykes, 16e Wagman and Trawick 16f ), Azotobacter vinelandii 

 (cf. Gilchriest and Boch 16g ), yeast, 45 higher plant tissues, 46 liver (cf. Peter- 

 mann et al., 16b Hall and Doty 16h ), pancreas, 39 tumor tissue 35 (cf. Petermann 



42 M. L. Petermann, M. G. Hamilton, and N. A. Mizen, Cancer Research 14, 360 

 (1954). 



43 H. K. Schachman, A. B. Pardee, and R. Y. Stanier, Arch. Biochem. Biophys. 38, 

 245 (1952). 



44 A. Tissieres and J. D. Watson, Nature 182, 778 (1958). 



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



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



