BIOLOGICAL ROLE OF PENTOSE NUCLEIC ACIDS 503 



part of the microsomes. Dipeptidase seems to be, in the amcBbse, a soluble 

 enzyme (see Holter,'^^ Holter and Pollock^^^ for a discussion of the intra- 

 cellular localization of enzymes in amoebae). 



Another unicellular organism, the alga Acetabularia mediterranea, pro- 

 vides much more decisive proof that protein synthesis can go on for a long 

 time in the absence of the nucleus: as shown already by Hammerling's^^^ 

 beautiful experiments, a nonnucleated half can regenerate to a fairly large 

 extent. Quantitative studies by Vanderhaeghe^^^ have definitely shown 

 that this regeneration is accompanied by an increase in dry weight and in 

 protein; these synthetic processes go on for a fortnight at the same rate 

 in the nucleated and nonnucleated halves; they then slow down and stop 

 gradually in the enucleated half, which is, however, able to survive for 

 several months. Experiments by Brachfet and Chantrenne^"'^^^ with radio- 

 active CO2 have confirmed and extended these findings: incorporation of 

 this precursor in the proteins is perfectly normal in nonnucleated halves 

 for 2 weeks, when it begins to decrease. Nonnucleated halves are also able 

 to incorporate radioactive glycine into their proteins (Brachet and Bry- 

 gjgj.159) ; it is interesting to note, in this respect, that while incorporation of 

 CO 2 into the proteins occurs almost exclusively in the chloroplasts and is 

 dependent on light supply, incorporation of glycine is more active in the 

 microsomes than in the chloroplasts and is not affected by light : two differ- 

 ent protein-synthesizing mechanisms, both largely independent of the 

 presence of the nucleus, thus exist in this alga. Finally, it has been shown 

 (Brachet and Chantrenne,^^" Chantrenne, Brachet, and Brygier'®') that 

 nonnucleated halves of Acetabularia, as well as nucleated ones, react to 

 the addition of hydrogen peroxide to the medium by increased catalase 

 activity, apparently due to adaptive synthesis: this capacity for increased 

 catalase activity or production slows down in nonnucleated halves after 1 

 week, but it still exists in cytoplasmic fragments which have been removed 

 from the nucleus for as long as 3 months. 



These experiments clearly show that the nucleus exerts only a remote 

 control on protein synthesis in this material: incorporation of amino acids 



" H. Holter, Advances in Enzymol. 13, 1 (1952). 



" H. Holter and B. M. Pollock, Compt. rend. trav. lab. Carlsberg, Ser. chim. 28, 221 



(1952). 

 ^^ J. Hammerling, Wilhelm Roux, Arch. Entwicklungsmech . Organ. 131, 1 (1934). 

 ^* F. Vanderhaeghe, Arch, intern, physiol. 60, 190 (1952). 

 " J. Brachet and H. Chantrenne, Nature 168, 950 (1951). 

 ^* J. Brachet and H. Chantrenne, Arch, intern, physiol. 60, 547 (1952). 

 " J. Brachet and J. Brygier, Arch, intern, physiol. 61, 248 (1953). 

 ^o J. Brachet and H. Chantrenne, Arch, intern, physiol. 61, 246 (1953). 

 " H. Chantrenne, J. Brachet, and J. Brygier, Arch, intern, physiol. 61, 419 (1953). 



