Biosynthesis Of Deoxyribonucleic Acid Research Articles

Studies on the biosynthesis of deoxyribonucleic acid in extracts of mammalian cells II. The enzymic formation of deoxyribonucleoside triphosphates

Extracts of the Ehrlich ascites carcinoma of the mouse prepared by centrifuging the disrupted cells at 105,000 × g, have been shown to contain enzymes capable of phosphorylating the monophosphates of deoxyadenosine, deoxycytidine, deoxyguanosine and thymidine to the corresponding triphosphates. The mobilities of these deoxyribonucleotides in a number of solvent systems are described.

Studies on the biosynthesis of deoxyribonucleic acid by extracts of mammalian cells I. Incorporation of [ 3H]thymidine

A particle-free extract has been prepared from Ehrlich ascites tumour cells disrupted sonically or osmotically which promotes the incorporation of [ 3H]thymidine into DNA in the presence of ATP, Mg ++ ions and carrier DNA. With sonic extracts glucose and DPN in high concentrarions are required for good incorporation; with osmotic extracts a low concentration of DPN suffices. Incorporation is diminished by dialysis and is promoted by low concentrations of deoxyribonucleoside monophosphates and to a greater extent by deoxyribonucleoside triphosphates. Evidence is presented that incorporation is preceded by conversion of [ 3H]TDR to [ 3H]TTP. Degradation of the [ 3H]DNA yields among other products [ 3H]thymidine diphosphate. Investigation of extracts from a series of different tissues shows that ability to incorporate [ 3H]TDR into DNA is greater in tissues of high mitotic activity.

Effect of Isologous Bone Marrow and Antibiotics in Mice after Supralethal X-Irradiation (1000 to 1100 r)

It is widely recognized that the acute radiation after exposure to penetrating ionizing radiations in the lethal dose range is the resultant, primarily, of injury to the gastrointestinal epithelium, on the one hand, and the bone marrow and lymphoid tissues, on the other (1-3). At supralethal whole-body X-radiation dose levels in the mouse, of the order of 1100 r, it is known that the acute radiation syndrome (4, 5), characterized by early (4to 6-day) radiation mortality, is the predominant mode of death. In contrast, at radiation doses of 800 r (an LD0oo dose), the great majority of untreated mice die during the second and third weeks postirradiation as a consequence of a involving defects in the hematopoietic system, and infection (5). The latter is known to be amenable to therapy by parenterally administered bone marrow cell suspensions, spleen homogenates, and spleen implants, which elicit accelerated regeneration of the hematopoietic tissues (6-9), and retard or prevent infection (10, 11). Our knowledge of the pathogenesis of the intestinal phase of acute radiation death (5, 12) and other related data in the literature (9, 13-16), suggest that radiation injury to the intestinal mucosa and subsequent regeneration processes are largely independent of the corresponding events in the hematopoietic tissues. Thus, accelerated regeneration of deoxyribonucleic acid biosynthesis in bone marrow and spleen of X-irradiated animals, induced by injection of bone marrow cell suspensions or spleen homogenates, is not accompanied by accelerated regeneration of intestinal mucosa (9, 16). In view of these considerations it was of interest to investigate the effect of isologous bone marrow injection on mice exposed to whole-

Effect of the deoxyriboside of 6-azathymine (azathymidine) on the biosynthesis of deoxyribonucleic acid by bone marrow and neoplastic cells ( in vitro)

Incorporation in vitro of radioactive formate into the bases of the DNA of rabbit bone marrow and Ehrlich ascites tumor cells was related predominantly to the formation of thymine. Thymine deoxyriboside by dilution, and 6-azathymine deoxyriboside and Aminopterin by inhibition, caused a marked decreased in the utilization of formate for the biosynthesis of DNA-thymine. Deoxyuridine and deoxycytidine each may serve as an acceptor of formate-carbon for the biosynthesis (of the methyl group) of DNA-thymine. Certain implications of these findings are discussed.