Sec. 25.7] MAJOR ORGANIC METABOLITES 519 



yields from the cyclotron by the reaction P 31 (d, p)P 32 and in the uranium pile 

 by the reactions P 31 (n, t)P 32 and S 32 (n, p)P 32 . 



The mineral metabolism of phosphorus has been investigated by a number 

 of workers. It was early found that phosphorus rapidly appears in the bone 

 and that there was a slow but definite turnover of bone phosphates [P77,78]. 

 The excretion of phosphorus was shown to take place through both urine and 

 feces [P196], although less than 10 per cent escaped by the latter route. 

 Other studies have demonstrated the rates at which the inorganic plasma 

 phosphate becomes incorporated into the organic metabolic pool [P64,194, 

 etc.] and the permeability of erythrocytes [P102,167,189] anc ] other cellular 

 membranes to the phosphate ion [P51,207]. 



The major tracer studies with P 32 in intermediary metabolism have been 

 on the formation and fate of two important classes of organic compounds: the 

 phospholipids [see Chaikoff and Zilversmit's review, P66] and the nucleo- 

 proteins [see Hevesy's review, P188]. It has been demonstrated that the 

 main site of phospholipid production for systemic use is the liver, although 

 the kidney, intestinal mucosa, brain, and muscle synthesize their own phos- 

 pholipid independently of the liver. Considerable work has been done on 

 the turnover of ribose- and desoxyribosenucleoprotein in various tissues. 

 When labeled inorganic phosphate is administered to the mammal, it is 

 distributed in the nucleic acid moiety of the nucleoprotein of all tissues. 

 Furthermore, this distribution correlates with the known metabolic and 

 growth characteristics of the various tissues. Desoxyribosenucleic acid, 

 being a nuclear constituent, turns over at a much greater rate in such rapidly 

 growing tissues as the spleen, growing liver, and neoplasms, than in the adult 

 liver, the cells of which, while metabolically very active, are not undergoing 

 many mitoses. Ribosenucleic acid on the other hand, being largely a cyto- 

 plasmic constituent, turns over in the liver as much as thirty-three times 

 as fast as desoxyribosenucleic acid; it also has a high turnover rate in the 

 spleen and intestinal mucosa. Such facts correlate well with the known 

 importance of those organs in protein metabolism and with the hypothesis 

 that the ribosenucleotides play a role in the synthesis of proteins. 



P 32 has also found an important role in the treatment of certain blood 

 dyscrasias (see Chap. 29). 



Despite the wide and intensive application of this isotope, its potentialities 

 in the study of vital processes have been by no means exhausted. 



