STUDIES OF RII3OSE METABOLISM. I. THE PATHWAY OR NUCLEIC ACID RIBOSE SYNTHESIS IN A HUMAN CARCINOMA CELL IN TISSUE CULTURE'

An impressive body of evidence is available demonstrating the importance of the pentose phos-phate pathway (hexose mnonophosphate shunt) in the intermediary metabolism of carbohydrate (1). The pathway is involved in a number of vital bio-logical processes, including photosynthesis (2), carbohydrate utilization by many bacteria (3), the elaboration of the ribose moiety of nucleic acids in the chick (4), in certain microorganisms (5-8), and in the rat (9, 10), the synthesis of the pre-cursor of aromatic amino acids (11), and the gen-eration of reduced triphosphopyridine nucleotides, which are required for the synthesis of several sub-stances including fatty acids and cholesterol (12). In addition, it is the route by which a substantial fraction of glucose is catabolized by rat liver slices (13). Recent work has demonstrated its role in the in vivo conversion of ribose and xylose carbon to mouse liver glycogen (14). The present investigation was undertaken to study the mechanism of nucleic acid ribose syn-thesis by a human carcinoma cell (strain HeLa) grown in tissue culture. The results are consistent with ribose production via both the oxidative and nonoxidative steps of the pentose phosphate path-way, with the nonoxidative route predominating. METHODS Tissue culture. A human carcinoma cell (strain HeLa) and a human liver cell (Henle, strain 407) were grown in the amino acid-vitamin-salt-glucose medium described by Eagle (15) supplemented with 5 per cent whole horse serum. After two or three days of incubation, at which time the inoculated cells were firmly adherent to the wall of the 1-liter Blake bottle in which they were grown, the C14-labeled substrate was added in the amount de-scribed. The medium was renewed every second or third 1 studies were supported by grants from th