693 



Shigetoh Miyachi 



stable P^^ in RNA -nucleotides (RNA-P^^) increases slowly while nucleo- 

 tidic labile P "^ decreases slowly under photos ynthetic condition indicate 

 that the nucleotidic labile P is not a simple hydrolysis product of RNA 

 but it may be labile P-compound(s) combined with nucleotides. We have, 

 however, no evidence to judge whether this labile compound is inorganic 

 polyphosphate or not. 



Our study revealed that Chlorella cells contain at least two groups of 

 polyphosphate which function differently; one group, poly-P"C" and poly- 

 P"A", plays a role as intermediate for the syntheses of intracellular P- 

 compounds which transfer P to the substances such as DNA and P-protein 

 under normal condition, and another group, poly-P"B" and poly-P"D", 

 functions as P reservoir but not as an energy reservoirV^^' -^^^j as con- 

 cluded by Harold(-^^) for Neurospora. 



Little is known of the path by which P from poly-P"C" and poly-P"A" 

 is transferred to other cellular compounds such as DNA and P-protein, 

 except the fact that the mobilization takes place only in the light. ADP is 

 generally considered to be the acceptor of P from polyphosphates. It may 

 also be possible, however, to assume the direct transfer of P from poly- 

 phosphate. The recent discovery by Szymona^ ' with M y c obac te r i um of 

 an enzyme which catalyzed the formation of glucose -6-P from polyphos- 

 phate and glucose suggests at such a possibility. 



One may assume that photos ynthetic or respiratory ATP is the pre- 

 cursor of polyphosphate in Chlorella. In this connection, Harold found 

 that the accumulation of polyphosphate caused by the addition of phosphate 

 to phosphate -starved mycelium of Neurospora is always preceded by ATP 

 accumulation and that the turnover of this compound is very rapid, sup- 

 porting the view that ATP is the metabolic precursor of polyphosphate in 

 this organisms. The data we obtained indicate that, at least a part of 

 poly-P"A" is not synthesized directly from extracellular orthophosphate 

 but through intracellular P-compounds and the process is light -independ- 

 ent. By our previous study with synchronized Chlorella cells' s it was 

 found that the amount of P incorporated into poly-P"A" and some other P- 

 compounds from other intracellular P-compounds increases gradually 

 with the progress of culture, attains the maximum level at the stage of 

 ripening, and decreased markedly during the process of "post ripening" 

 and "division" of cells indicating that these compounds are playing an 

 important role in the process of cell maturation and division. As the con- 

 comitant decrease of P with the increase of poly-P"A" was observed only 

 in poly-P"C", it was inferred that poly-P"A" received P from poly-P"C". 

 In our dark experiment, however, decrease of poly-P "C" concomitant 



