Abstract
Summary
The measurement of DNA turnover in bone marrow of the rat is influenced by the type of labeled precursor chosen as tracer. After a single injection of H3-thymi-dine (0.1 μC/g body weight, spec. act. 1.9 C/mM) or of C14-thymidine (0.01 μC/g body weight, spec. act. 30 mC/mM). the specific activity of DNA declined from day 1 to day 9 in a simple exponential manner with a half time of approximately 2 days (46 hours). However, after injection of 5-I131-deoxyuridine (0.18 μC/g body weight, spec. act. higher than 30 C/mM), the respective half time was approximately 1.2-1.3 days (30 hours). The difference in rates of regression of DNA specific activity was discussed and attributed to reutilization of thymidine and to minimal or absent reutilization of 5-iodo-deoxyundine. The parallel regression of C14-and of H3-labeled DNA after single injection of respectively labeled precursor indicates that kinetic isotope effects do not interfere with the measurement of the reutilization pathway. The magnitude of the reutilization pathway is estimated to involve 35-40% of the thymidine which is released from DNA by catabolism. The data presented here confirm thymidine to be a major contributor to the reutilization pathway. No estimates can be made with regard to the additional possible participation of nucleotide chains in the intercellular transfer of DNA catabolites.
Get full access to this article
View all access options for this article.