691 



COMMKNT ON PAPERS 67 — 70. 



We started our investigations on the application of radio-phosphorus as a tracer 

 with the study of the incorporation of ^ap into the minoial constituents of the 

 skeleton, then took up the study of the formation of labelled phosphatides and 

 acid-soluble compounds. In 1939 an investigation of incorporation of ^^p into 

 desoxyribonucleic acid was started. A note on the results of these studies was 

 published by Hahn and Hevesy (1940) and a more detailed account is given 

 in paper 67. Outgrown organs which do not secrete DNA containing leucocytes as 

 the liver and kidney were found to incorporate minimal amounts of ^^P into DNA 

 only. The spleen which secretes leucocytes incorporates appreciable amounts 

 of ^^P into its DNA since the secreted molecules have to be replaced and the new 

 formation of DNA molecules takes place under the incorporation of ^^p. The 

 production of labelled DNA molecules is very pronounced in the intestinal mucosa 

 in which the cells destroyed in the course of the digestive processes have to be 

 replaced. In paper 67 it is stated that " The rate of renewal of the nucleic 

 acid in the liver may be identical with the rate of formation of liver cells". 

 A statement, supported by the results of recent investigations. 



In later studies (paper 68) the rate of formation of both labelled DNA and ENA 

 was investigated. In the meantime Brues et al. (1944) found, in experiments tak- 

 ing over a week, the latter to be larger than the former. The very great difference 

 between the incorporation of ^ap into DNA and the UNA of the rat liver was 

 brought out in the investigation described in paper 68 in which incorporation was 

 determined after 2 hr only. The specific activity of RNA phosphorus was found 

 to be thirty-three times as large as that of the DNA phosphorus. In the spleen 

 and intestine in which DNA is built up at a rapid rate the corresponding ratio 

 makes out 3 and 2 only. In the rapidly growing Jensen-sarcoma of the rat in which 

 formation of DNA takes place at a very appreciable rate as it does in the spleen 

 and in the intestinal mucosa, the corresponding ratio was found to be 2.4 (pa- 

 per 69). The great stabihty of the DNA present in nucleated erythrocytes mad. 

 it possible to determine the previously unknown Ufe cycle of avian red corpuscles. 

 Doubts were expressed on the correctness of the results obtained when these were 

 communicated at the Solvay Congress in Brussels.Their correctness was, however, 

 brought out by later investigations (ShemIn, 1948; Ottesen, 1955). Since those 

 early days when ^ap was first incorporated into DNA, labelled desoxyribonucleic 

 acid found a very extended apphcation in numerous studies. 



References 



A. M. Brijes, M. M. Tracy and W. E. Cohn (1944) J. Biol. Chem. 155, 619. 



L. Hahn and G. Hevesy (1940) Nature 145, 549. 



J. Ottesen (1955) The Life-Cycle Of Hen Erythrocytes. Ejnar Munksgaard, Copen- 

 hagen. 



D. Shemin (1948) Cold Spring Harbour Symphosia On Quantitative Biology 13, 

 185. 



44* 



