784 ADVENTURES IN RADIOISOTOPE RESEARCH 



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1 mgm of the desoxyribonucleic acid obtained had an activity of up 

 to2000 counts per minute. Thus, 0.05 mgm of P split off from this sub- 

 strate was determined without difficulty by activity measurements. The 

 nucleic acid, which is highly polymerised in the beginning, becomes 

 depolymerised to a certain extent in the course of the purification process, 

 and had a molecular weight of about 14,000 only. 



In our investigations we use a few mgm or less of labelled substrate, 

 which was added to the plasma of a rat, and the plasma was kept at 

 37° for a definite time. After cooling with ice, trichloracetic acid was 

 added, and both the precipitate and the filtrate were secured. The 

 precipitate contained the non-spUt nucleic acid, while the filtrate was 

 found to contain not only labelled inorganic phosphate but also an 

 organic acid-soluble fraction containing labelled phosphate. By com- 

 paring the activities of the different fractions we obtained figures for the 

 percentage formation of inorganic and organic acid-soluble P, due to 

 enzymic action. 



The inorganic phosphate was precipitated from an aliquot of the 

 filtrate after adding 80 mgm of inactive sodium phosphate as ammonium 

 magnesium salt. Another aliquot was used for colorimetric determina- 

 tion of inorganic phosphorus. A third aliquot was ashed, and from the 

 solution obtained the P was precipitated as described above. The dif- 

 ference between the total acid-soluble P and the inorganic P corresponds 

 to the organic acid-soluble P spHt off owing to the action of enzymes 

 from the nucleic acid added. 



EFFECT OF BLOOD PLASMA PHOSPHATASE ON NUCLEIC ACID 



To begin with, we compared the phosphatase activities of the blood 

 serum of 6 weeks old normal rats and rats with Jensen-sarcomata. 

 7.02 mgm of labelled desoxyribonucleic acid was dissolved in 15 ml of 

 serum. The radioactivity of 2 ml was measured at once, and the radio- 

 activity of an equal volume of solution was determined after it had been 

 kept at 37° for 2 and 24 hours respectively. The nucleic acid concentra- 

 tion was 1.17 mgm (0.1 mgm nucleic acid P) per ml of plasma. The protein 

 and unchanged nucleic acid present were precipitated by adding 2 ml 

 of 10 per cent trichloracetic acid, the precipitate was centrifuged, washed 

 with further 2 ml trichloracetic acid and the activity of the sample 

 determined. An aliquote of the filtrate was ashed and its total phosphorus 

 content secured as magnesiumammonium phosphate. From an other 

 aliquote of the filtrate the inorganic phosphate was precipitated. We 

 investigated thus 3 fractions: 



(a) Protein, (b) Inorganic P, (c) Total acid-soluble P. 



