MOLECULAR REJUVEXATIOX OF MUSCLE TISSUE 



367 



muscle we are faced with a molecular rejuvenation of the creatine phos- 

 phoric acid to the above extent. The adenosin and the hexosephosphate 

 molecules arc rejuvenated to about the same extent as those of the 

 creatine phosphoric acid. Witli increasing temperature, as is to be 

 expected, the rate of molecular rejuvenation increases, and in the course 

 of less than a day practically all creatine phosphoric acid molecules are 

 renewed. 



Phosphorus Isolated from Frog Killed 3 Hours after 

 Subcutaneous In.tection of Labelled Sodium Phosphate 



Relative specific activity 

 (activity per mgm V) 



Prog kept at 2° 



Inorganic P 



Creatine P 



Adenosin P (7 min hydrolysed at 100°) 

 "Hexose" P (30 min hydroly.sed at 100°) 

 Product of 100 min hydrolj'sis at 100" 

 Non-acid soluble residual fraction . . 



Frog kept at 21° 



100 



78 



78 

 38 



The new formation of some of the 'acid soluble' phosphorus compounds 

 present in the blood also takes place to a very appreciable extent. In 

 human blood 2 hours after intravenous injection of labelled sodium 

 phosphate, the specific activity of the total acid soluble organic phos- 

 phorus, kindly extracted by Mr. A. H. W. Aten from the blood cor- 

 puscles, amounted to 20 per cent of that of the plasma inorganic phos- 

 phorus. 



In experiments in vitro^'^Hn which dog's blood was shaken for 2.5 

 hours with labelled sodium phosphate, 1/25 of the total acid soluble 

 molecules was found to be labelled and thus split and resynthesized 

 under the action of enzymes. In the same in vitro experiments the for- 

 mation of only very minute amounts of labelled phosphatides (less 

 than 0.1 per cent) could be ascertained. Also in experiments in vivo 

 labelled phosphatides were found to be present to an appreciable extent 

 in the blood only after much longer time. The specific activity of phospha- 

 tide P extracted from human blood corpuscles 24 hours after administra- 

 tion of labelled sodium phosphate was found to be 40 times less than 

 that of plasma inorganic P, showing the very low rate of rejuvenation 

 of the phosphatide molecules present in the blood. 



There is thus a conspicuous difference in the rate of rejuvenation of 

 some low molecular water soluble compounds, as for example, creatine 

 phosphoric acid, adenosin phosphoric acid, hexosephosphate, and 

 non-w^ater soluble products like phosphatides, nucleoproteins and similar 



