462 ADVENTURES IN KADIOISOTOPE RESEARCH 



genous inorganic P were found not to dialyse. The non-dialysing in- 

 organic phosphate is presumably combined with proteins. That a minor 

 part of the inorganic P of the plasma is bound to proteins is also made 

 very probable by previous work in which other methods were used and 

 which are discussed below. 



As seen in Table 1, the total acid-soluble P content was found to be 

 appreciably higher than inorganic P content, about ^5 of the acid- 

 soluble P being present in organic binding. The specific activity of the 

 total acid-soluble P Avas found to be lower than the corresponding value 

 of the inorganic P, indicating that the labelled phosphate does not 

 interchange or interchange to a minor extent only with the organic P 

 present in the plasma. 



PREVIOUS WORK ON THE PRESENCE OF PHOSPHATE-PROTEIN 



COMPOUNDS IN THE PLASMA 



Macheboeuf and S0rensen (1925/27) in their studies on the com- 

 position of egg-albumin were led to the result that between the large 

 complexes which are constituting egg-albumin molecules few phosphorus 

 containing complexes are present ; these are bound so firmly to the 

 other groups of the molecule that they have to be considered a con- 

 stituent of the latter. The amount of protein-bound phosphorus was 

 found in albumin, resp. globulin to amount to 7.5 resp. 2 mgm per gm 

 total nitrogen. This phosphorus could not be separated from albumin, 

 resp. globulin, by electrodialysis. S^rensen (1925/27) investigated on 

 similar lines the phosphorus content of serum-albumin and serum- 

 euglobulin. Serum albumin and euglobulin were found to contain 2 — 40, 

 resp. 0.15-0.3 mgm P pergm total nitrogen. In contrast to the phosphorus 

 of egg proteins only a small percentage of the phosphorus of the serum 

 proteins could be precipitated by alcohol. This and other observations 

 induced S0rensen to regard the serum protein P as an accessory con- 

 stituent of the serum proteins only. No conclusions can be drawn from 

 these investigations if this accessory phosphorus is getting into exchange 

 equilibrium with the comparatively large amounts of inorganic phos- 

 phorus simultaneously present in the plasma or not. 



Masket et al. (1942) analysed fractioned centrifuged horse serum 

 and found that the inorganic phosphorus concentration increases 

 progressively with the protein concentration. Differences of 0.14 and 

 0.15 mM of P per kilo water were obtained between the top and bottom 

 fraction, the top fraction containing 11% less, the bottom fraction 12% 

 more inorganic P than the unfractionated plasma which contained 

 1.3 mM per kilo of HoO. These authors conclude from their results that 

 phosphate-protein compounds normally occur in horse serum. 



