236 TORE HULTIN et al. 



25. Rendi, R., Exp. Cell Res. 19, 489 (i960). 



26. Rendi, R., and Hultin, T., Exp. Cell Res. 19, 253 (i960). 



27. Selby, C. C.,J. biophys. biochetfi. Cytol. I, 429 (1955). 



28. Siekevitz, V.,y. biol. Chem. 195, 549 (1952). 



29. Siekevitz, P., Exp. Cell Res. Suppl. 7, 90 (1959). 



30. Spiegelman, S., in "Symposia of the Society for Experimental Biology", 

 ed. F. Danielli and R. Brown. University Press, Cambridge, 286 (1948). 



31. Ts'O, P. O. P., Bonner, J., and Vinograd, J., ^. biophys. biochem. Cytol. 2, 

 451 (1956). 



32. Wieland, T., in "Festschrift Arthur Stoll", ed. P. Karrer et al. Birkhauser, 

 Basel, 582 (1957)- 



33. Zamecnik, P. C, and Keller, E. B.,J. biol. Chem. 209, 337 (1954). 



Discussion 



Williams : Korner has reported effects of insulin and growth hormone on 

 amino acid incorporation, and I was wondering if you had confirmed these effects. 



Hultin : No. I do not think that Korner's experiments say very much about 

 whether a high content of ribonucleoprotein particles has been induced or whether 

 the particles already available work more efficiently in the system, but I should 

 like to test that possibility. 



Siekevitz: One other explanation of your results is this: In the liver cells some 

 RNP particles are on the membrane and some others are free, and when you mea- 

 sure the incorporation you measure the protein radioactivity in these mixed kind 

 of particles. These particles are possibly synthesizing proteins at different rates 

 and are perhaps also synthesizing different kinds of proteins. So that when you 

 think you are making these particles increase they synthetic ability, what you 

 might be really doing is changing the ratio from the normal state, the ratio of bound 

 to free particles. You, therefore, might be switching over the synthesis from one 

 kind of protein to another kind of protein which has a higher rate of synthesis. 



Hultin : I have also been considering that kind of possibility and also the 

 possibility that particles may be released from the membrane and therefore work 

 better. I am not quite convinced that a major change in the population pattern 

 of the particles would be the right explanation in the case of the just fertilized sea 

 urchin egg. 



Packer: Both you and Dr. Siekevitz are implying that what has happened is 

 that changes in structure are simultaneously occurring, and I was wondering 

 whether it would not be possible to devise an experiment, at least in an in vitro 

 system, where you could simultaneously follow a parameter in physical structure 

 and one in the function activity, such as viscosity determinations, light scattering 

 determinations and sedimentation velocity. 



Hultin : Yes, perhaps under certain conditions what you call ergastoplasm 

 may form some sort of sandwich which may become released, so that particles 

 attached to this open sandwich may act more rapidly by becoming more easily 

 supplied with energy and amino acids. 



Zamecnik: There is another possible site of operation of a regulator of protein 

 synthesis. Data of Dr. Tissieres et al. {Proc. nat. Acad. Sci., Wash. 46, 1450-1463 



