Chapter 10 



EFFEC^r OF NEUTRONS ON THE RIBONUCLEINASE IN RABBIT 



BLOOD AND TISSUES 



By CHARLES A. ZITTLE 



X'ariations in the ultraviolet light absorption of cells in biopsy specimens 

 after irradiation with therapeutic doses of X-rays and gamma rays found 

 by Mitchell (1) led to the conclusions that there is an accumulation of 

 ribonucleic acid products in the cytoplasm and a cessation of synthesis 

 of desoxyribonucleic acid in the nucleus. Disturbances in the metabo- 

 lism of l)oth ribonucleic and desoxyribonucleic acids on irradiation with 

 ionizing rays was brought out in later papers by Mitchell as well (2, 3), 

 effects which were considered to be due to inacti^•ation of catalyst mole- 

 cules, presumably components of enzyme systems. Studies by Marshak 

 (4) also suggest an involvement of nucleic acids in the effects of X-rays. 

 ]^y means of radioactive phosphorus (P32) in tracer studies a shift of the 

 phosphorus from the cytoplasm to the nucleus in lymphoma cells after 

 irradiation with X-rays was demonstrated. This shift is probably cor- 

 related with changes in the metabolism of nucleic acid since it contains 

 phosphoric acid. 



The above observations suggested that enzymes in\olvcd in the me- 

 tabolism of nucleic acid be investigated in animals treated with neuti-ons, 

 since the fundamental biologic effects of X-rays and neutrons have been 

 assumed (5) to be the .same and dependent on the tlegree of ionization pro- 

 duced within tissue cells. The ionizing rays, however, may affect di- 

 rectly the nucleic acids and these in turn influence enzymiCS (i.e., dehvdio- 

 genases) (6). 



The present studies have been made on ribonucleinase, the enzyme which 

 catalyzes the depolymerization of ribonucleic acid with the formation of 

 mononucleotides (7), since a convenient manometric procedure was avail- 

 able (8) for its determination, and since its content in the blood and tissues 

 of normal rats and rabbits has been reported (9). The content of this 

 enzyme in the tissues of irradiated rabbits is reported herein. 



Studies are desirable with the enzymes which hydrolyze desoxyribonucleic 

 acid as well. The enzyme which depolymerizes desoxyribonucleic acid 

 has been purified (10) but hydrolysis of nucleic acid by this enzyme appar- 

 ently stops at the tetranucleotide stage (11). Further hydrolysis to mono- 

 nucleotides and nucleosides is brought about by a phosphoesterase from 

 calf intestinal mucosa and other tissues (12-16), which is not highly specific, 



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