Maxwell L. Eidinoff

Incorporation of unnatural pyrimidine bases into deoxyribonucleic acid of mammalian cells.

When a mammalian cell strain was incubated with 5-iododeoxyuridine and 5-bromodeoxyuridine, DNA thymine was partially replaced by the halogen-containing pyrimidines. The extent of incorporation of the unnatural bases increased when amethopterin and hypoxanthine were added to the medium. It is thus evident that the replacement of DNA thymine by selected structural analogs, a phenomenon previously reported for bacterial systems, is applicable to cells of higher organisms.

ISOTOPIC STUDIES OF PLASMA CHOLESTEROL OF ENDOGENOUS AND EXOGENOUS ORIGINS

This study was undertaken in order to compare the metabolic behavior of plasma cholesterol derived from the diet with that of cholesterol synthesized in vAvo from acetate (1). Cholesterol labeled with either isotopic carbon or hydrogen was administered orally to human subjects and the incorporation into plasma cholesterol was followed over an extended period. In certain instances, both endogenous and exogenous cholesterol metabolism were studied simultaneously by the use of appropriately labeled acetate and cholesterol. These techniques were also applied to an examination of the behavior of plasma cholesterol in four patients with hypercholesterolemia.

Effect of 5-bromodeoxyuridine on nucleic acid and protein synthesis and viability in HeLa cells

Abstract 1. A mitotically synchronized population of HeLa cells was exposed to 5-bromodeoxyuridine for 3-h intervals spaced over the entire division cycle. The maximum loss in cell viability took place when the exposure to 5-bromodeoxyuridine occurred during the interval when the rate of DNA synthesis was a maximum. 2. Following a 24-h exposure to the analog, DNA synthesis was inhibited in the subsequent replication cycle whereas RNA and protein synthesis was slightly reduced. 3. The activity of DNA polymerase (deoxynucleoside-triphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) and uridine kinase (ATP:uridine 5′phosphotransferase) was reduced by a significantly large percentage relative to changes in total cellular protein. This may imply alteration in functional protein consequent to the replacement of DNA thymine by 5-bromouracil.

Tritium in Biochemical Studies

TRITIUM AS A LABEL When a portion of a biochemically interesting compound, such as methyl or phenyl, etc., remains intactthroughout the experiment, then the hydrogens attached to the carbons may serve as a label for the carbons, or for the ring system. In this way, a purine or pyrimidine ring, a steroid framework, the phenyl group of an aromatic amino acid, a portion of fatty acid, has been used, when suitably labeled with tritium, as a marker forthe group in question. This was one of the important uses for deuterium in biochemical systems, as shown in the pioneering work of Schoenheimer, Rittenberg, and numerous other investigators. In the text by Kamen, Radioactive Tracers in Biology, there is a chapter listing compounds containing deuterium and references are given to some applications with these compounds. It is, thus, simply necessary to state that those examples using stably bound deuterium carry over exactly to the use of tritium in those positions.