510 J. BRACKET 



There are, nevertheless, a few indications in favor of the existence 

 of phosphorylated PNA. It has been recently reported by Bressler and 

 Nidzyan^"^ — and confirmed in this laboratory — that if ATP labeled with 

 P*2 is mixed with PNA in the presence of a liver homogenate, part of the 

 radioactive P is transferred to PNA or, at any rate, to a substance absorb- 

 ing ultraviolet light and resembling PNA chromatographically. 



In a paper dealing with the use of firefly luminescence for ATP estima- 

 tion, Strehler and Totter^''^ incidentally report that some purified PNA's 

 have been found to have "ATP" activity; this activity does not disappear 

 after treatment with ribonuclease. It is interesting to note that, according 

 to Strehler and Totter,^''^ PNA's from growing yeast cultures have "ATP" 

 activity, while samples from dormant cultures do not. 



While these findings provide interesting hints that phosphorylation of 

 PNA might be a step in protein synthesis, it must be admitted that the 

 evidence is still too meager to allow any definite conclusion. At the present 

 time, we are still unable to decide whether peptide synthesis is due to 

 reversal of proteolysis or to intermediate phosphorylation reactions, or to 

 both; and the difficulties of explaining protein specificity are even more 

 formidable. 



c. The "Template" Hypothesis 



For the biologist, especially the geneticist and the immunologist, the 

 major problem to be solved is the mechanism of specific protein synthesis 

 rather than the nature of the energy-yielding reactions. The problem here 

 is merely at the stage of ingenious hypotheses, the major one, for which 

 there is no satisfactory substitute so far, being the so-called template 

 hypothesis, which postulates the existence of a model (template) under the 

 influence of which the building blocks, whether they are amino acids or 

 peptides, are arranged in the right order. The template would act as a 

 mold forming a counterpart to the protein to be formed. It is tempting to 

 suppose, as many have already done (Friedrich-Freksa,^*'' Rondoni,^''^ 

 Haurowitz,i73,i8o,i8i ^nd Caldwell and Hinshelwood^"^), that it is PNA 

 which represents the counterpart to the protein. 



It would be fruitless to go into details of all these theories, but those of 

 Haurowitz'"'*"''^' and of Caldwell and Hinshelwood^o^ deserve further 

 mention. Haurowitz^''^ believes that protein synthesis takes part in two 

 successive steps. The first stage is the combination of amino acids to form 

 a definite species-specific peptide pattern; in the second phase, the peptide 



^o' S. E. Bresler and E. I. Nidzyan, Doklady Akad. Nauk S. S. S. R. 75, 79 (1950). 



202 B. L. Strehler and J. R. Totter, Arch. Biochem. and Biophys. 40, 28 (1952). 



203 H. Friedrich-Freksa, Naturwissenschajten 28, 376 (1940). 



204 P. Rondoni, Enzymologia 9, 380 (1940). 



206 p. C. Caldwell and Sir Cyril Hinshelwood, /. Chem. Soc. 1950, 3156. 



