88 ERNEST POLLARD 



POLLARD : It seems to me that within the cells there is no considerable protective 

 effect. 



EREERA: Did the cross-section of the protein synthesizing particles for the ^sg 

 incorporation coincide with that for the methionine? Were the cross -sections 

 comj^ared for the cells with deficient and adequate amino acid and nucleotide 

 supply? 



POLLARD : The first question we may answer in the affirmative, although it would 

 be interesting to determine the specificity of the methionine's behaviour com- 

 pared with that of its homologue. The second problem we have not yet studied 

 although we intended to in order to determine whether ribosomes can exist in 

 the extended as well as in the contracted form. 



PASSYNSKY: In the basic ec(uations \)i (h/do) = — ]I and In, {n/i^a) = SD the 

 values V and S are not the volume and real surface of the target in the strict 

 meaning of the word. They are but factors of probability, possessing the dimen- 

 sions of volume and surface, but they differ from these by dissimulated non-de- 

 nominated coefficients of proportionality K. If /v = 1, then these concepts coincide. 

 For pure proteins results may be compared with those obtained by other methods 

 and it could often be assumed that K = 1; this approach then gives some in- 

 teresting results. But with regard to such complex intracellular systems as systems 

 of protein biosynthesis or amino acid incorporation we cannot be sure that the 

 condition K = 1 always holds true, and in such cases the dimensions calculated 

 may differ considerably from the real values. 



POLLARD : That is cjuite correct. In model expei'iments on simple substances the 

 agreement was gootl enough. Unfortimately, for the study of protein synthesis 

 in a living cell there are no other ai:)proaches available to evaluate the dimensions 

 of the structures involved. 



We believe that our investigations contribute sonie information and deserve 

 some consideration along with other joroofs. It is possible that they have some 

 importance. 



BACQ : It is 2^ossible that the peculiar behaviour of methionine is accounted for 

 by its utilization by the cell not only for protein synthesis but for other functions, 

 for example, connected with methyl group transfer. 



POLLARD : This possibility exists for other amino acids too. 



TOBIAS: Irradiation with doses as large as 2 x 10^ r could produce membrane 

 lesions and loss of a quantity of certain substances (ions, nucleotides) from the 

 cell which could alter the calculated results. 



POLLARD: Within 1.5 minutes we have not seen any loss of substances with the 

 exception of arginine. Since there is an increase in cell mass we Ijelieve that 

 active protein biosynthesis was taking j:)lace. 



TUMERMAN : Are there data available on the use of the electron microscope for 

 the direct measiu-ement of the areas studied, since their flimensions are within 

 the resolution range of this method. 



POLLARD : While studying irradiated viruses and ribosomes of the irradiated cells 

 witli the electron microscope, no difference was found comjoared with non- 

 irradiated preparations. It is unlikely that this approach would allow us to discern 

 differences in the process of amino acid incorporation. 



