290 IV. THE PRINCIPLES OF LIFE PHENOMENA 



nucleic acids in the protoplasm is firstly to strengthen its template 

 pattern and secondarily to provide the energy for the protein syn- 

 thesis. 



As is well recognized, APT is involved in the energy metabolism 

 in the contraction of muscles. The muscle contraction, on the other 

 hand, is believed to be caused by expanding and contracting of the 

 component proteins, mainly a protein called actin. According to Szent- 

 Gyorgyi (115) ATP acts to expand the muscle protein and in case of 

 contraction ATP undergoes decomposition, yielding inorganic phosphate 

 and energy. Munch-Petersen (116) likewise showed that ATP expands 

 monolayers of myosin, another chief muscle protein. Mommaerts (117) 

 claimed that ATP is essential for the polymerization of actin. Poly- 

 merized actin can be separated from accompanying protein by ultracen- 

 trifugation. The separated actin, after dissolution and depolymerization 

 in water, does not polymerize again upon addition of salt, unless ATP 

 is present during the entire depolymerization process. He has further 

 reported that in a pure system a stoichiometric reaction takes place 

 between actin and ATP in which 1 mole of globular actin reacts with 

 1 mole of ATP, yielding actin in the polymerized form with the 

 liberation of energy and inorganic phosphate (118). These evidences 

 clearly indicate that ATP, the chief component of nucleic acid, has 

 the function to maintain the protein molecules in a definite form 

 while it can provide energy on the decomposition. The nucleic acid 

 in the protoplasm may behave in a similar way. 



Spicer and Rozsa (119) have found in an electron microscopic study 

 that actomyosin tends to form fibrous aggregates in the presence of 

 ATP. At a lower pH the tendency to form fibrous structures appears 

 even in the absence of ATP, and needle-like or spindle-shaped aggre- 

 gates are to be seen, but this tendency is intensified by the presence 

 of ATP, showing that ATP contributes to the stretch of the actomyo- 

 sin molecules. 



There are two kinds of nucleic acids, /. e., desoxyribonucleic acid 

 (DNA) and ribonucleic acid (RNA), but it seems probable that only 

 the latter is used as the energy donor, as it is confirmed that the 

 nucleic acid which increases in case of active protein synthesis is 

 RNA, not DNA. 



Histological and chemical studies on the distribution of RNA in 

 different tissues and microspectrophotometric researches have led to 

 the recognition of a constant coincidence in space and time of a high 

 content of RNA and rapid protein formation. When protein formation 

 or growth is taking place the RNA content is high, but when the 

 same cells are not producing proteins, there is less RNA (29). 



Davidson and Raymond (112) fed labelled ammonium citrate to 



