Protein and Polynucleotide Turnover 



209 



The maximum turnover in glycine in the proteins appeared 

 approximately 30 hours later (60 hours after partial hepatec- 

 tomy). All of the other amino acids also had a maximum at 

 this point, indicating a common maximum of transamination. 



The cytological changes during regeneration (Fig. 6) are 

 in accordance with earlier similar findings, and bear out the 

 conclusions from tracer analyses that nucleic acid turnover 

 and synthesis play the primary role in nucleic acid-protein 



Nudeus-CytopjQsmic Ratio 



168 

 Hours after the operation. 



Nucleic acid Protein 

 maxima. maximum. 



Fig. 6. Constituents of regenerating liver cell. In order to 

 facilitate comparison, the curves have been separated by multi- 

 plying each value by an arbitrary factor and adding a constant. 

 The maximum values, expressed as percentage increase of normal 

 liver cell constituents, are: nucleolus, 260; nucleus, 160; cyto- 

 plasm, 145; and nucleus-cytoplasm ratio, 130. The mitosis 

 frequency increased from less than 0.05 per cent in normal 

 liver to 10ii:0-32 per cent at 24 hours regeneration. 



formation. One notes the coincidence of the maximum rate 

 of polynucleotide synthesis with the maximum of mitosis 

 frequency and with the size of nuclei and nucleoli. Also it 

 can be seen that during the period of maximum protein syn- 

 thesis, at regeneration times 48-56 hours, these cytological 

 quantities have already diminished. 



In this connection I would like to mention some measure- 

 ments that have been made recently. The rats were fed by 



ISOTOPES 



15 



