406 



N. M. SISAKYAN 



intensively in the mitochondrial fraction. However, accumulation of protein 

 does not occur in these fractions. This is clearly to be explained by the occurrence 

 of intensive proteolytic processes at the same time as the incorporation of the 

 labelled compound. Although the metabolic rate of the chloroplast fraction is 

 low, as may be seen from the lower rate of incorporation of labelled glycine, a 

 very considerable increase in protein occurs there. 



Thus, the available facts and observations lead to the idea that the function of 

 protein synthesis is not associated with a strictly determinate structural organ- 

 ization but is brought about by various types of structures (nuclei, mitochondria, 

 microsomes) with a different degree of intensity and with peculiarities deter- 

 mined by the organoidal specificity of the proteins. 



The brilliant work of Gale and his colleagues [33, 34] has shown, quite recently, 

 that protein can be synthesized by disrupted bacterial cells. All this, taken 

 together, indicates the relative nature of the association of a biochemical function 

 with a particular structural organization and means that one must be very careful 

 how one uses the concept of the 'localization' of biochemical function. 



£•* 



Time. 



2 

 hr 



Fig. 2. Relation of the incorporation of [^■'C]glycine into the chloroplasts to 

 time of incubation. 



I — Without the addition of amino acids. 

 II — With a mixture of 15 amino acids. 



Comparison of the data derived from a comparative study of the synthesis of 

 the peptide bond in the protoplasmic structures of the animal and plant cell 

 reveals points of difference as well as points of resemblance. Differences are 

 present, not only in the localization of protein synthesis, but also in the chemical 

 mechanism of the actual process of the synthesis of protein in different structures. 

 The differences are to be seen in the kinetics of the process and also in the énergie 

 conditions, the optimum pH and the susceptibility to inhibiting substances. 



Thus, in homogenates of animal cells the incorporation of a labelled amino 

 acid into protein is directly proportional to the time of incubation of the homo- 

 genate with the labelled amino acid [35], while in the incorporation of labelled 

 glycine into the protein of the chloroplasts a hnear relationship between the 

 intensity of incorporation and time is not found. 



In Fig. 2 it may be seen that, during the first 35-40 minutes, the incorporation 

 of the labelled compound proceeds very fast. The process of incorporation is 



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