502 J. BRACKET 



of hemoglobin, it has been conclusively proved by Borsook et al.^^^''^" 

 that radioactive leucine and other labeled acids are quickly incorporated 

 into hemoglobin and other proteins. In the same laboratory, Holloway and 

 Ripley^^^ have shown that development of reticulocytosis is accompanied 

 by a substantial increase in the PNA content, which is closely paralleled 

 by the amount of radioactive leucine incorporated into the proteins. The 

 authors point out that their results are compatible with the view that 

 PNA is closely associated with amino acid incorporation into proteins; 

 it might be added that they are not compatible with the view that the 

 cell nucleus is the most important center of protein synthesis. 



Slightly different results have, however, been reported by Koritz and 

 Chantrenne,'*^ who find that the maximal rate of incorporation of labeled 

 glycine precedes the PNA maximum by 2 to 3 days; the PNA peak coin- 

 cides with maximal content of the red blood cells in hemoglobin, dipep- 

 tidase, and carbonic anhydrase. 



Nothing as yet is known about the capacity of nonnucleated Amoeba 

 halves to incorporate labeled amino acids into their proteins except the 

 fact that autoradiographic techniques show that such an incorporation 

 actually occurs 1 day after enucleation. But recent work by Brachet'^*'"'^*^ 

 and Urbani^^'^'*' has disclosed the interesting fact that different enzymes 

 — therefore different proteins — behave in a very dissimilar manner in non- 

 nucleated Amoeba halves: while protease, amylase, and adenosinetriphos- 

 phatase remain completely unaffected by the removal of the nucleus, 

 dipeptidase (as well as the total tyrosine-containing proteins: Brachet'^^) 

 markedly decreases during the first 3 to 4 days; it then remains constant 

 at a level which represents 50% of the amount present in the nucleated 

 halves. A third group of enzymes, including acid phosphatase and esterase, 

 remain constant for about 3 to 4 days and then drop sharply : they behave 

 exactly as PNA. 



These unexpected results show that the control exerted on protein 

 maintenance by the nucleus differs according to the protein studied; it is 

 very likely, but not yet definitely proved, that the enzymes which are 

 unaffected by the removal of the nucleus are bound to large granules, 

 comparable to the mitochondria, while those which behave like PNA are 



i^« H. Borsook, C. L. Deasy, A. J. Haagen-Smit, G. Keighley, and P. H. Lowy, Fed- 

 eration Proc. 10, 18 (1951). 



'" H. Borsook, C. L. Deasy, A. J. Haagen-Smit, G. Keighley, and P. H. Lowy, J. 

 B?oZ. C/iem. 196, 669 (1952). 



1^8 S. B. Koritz and H. Chantrenne, Arch, intern, physiol. 60, 549 (1952). 



1" J. Brachet, Biochim. et Biophys. Acta 9, 221 (1952). 



'50 E. Urbani, Arch, intern, physiol. 60, 189 (1952). 



'51 E. Urbani, Biochim. et Biophys. Acta 9, 108 (1952). 



'52 J. Brachet, Nature 168, 205 (1951). 



