Metabolic Inhibition of Mammalian Uridine Diphosphate Galactose 4-Epimerase in Cell Cultures and in Tumor Cells

• Published in: The Journal of biological chemistry 1966-06, Vol.241 (12), p.2737-2745
• Main Authors: Robinson, E A, Kalckar, H M, Troedsson, H, Sanford, K
• Format: Article
• Language: English
• Subjects: Chromatography, Paper; Culture Techniques; Galactose - metabolism; HeLa Cells; Hexosephosphates - metabolism; Isomerases - metabolism; L Cells; NAD - metabolism; Uracil Nucleotides
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)96526-9

The metabolism of galactose compounds, especially that of uridine diphosphate d -galactose, has been studied in intact as well as in broken L cells and HeLa cells. It has been shown that the incorporation of d -galactose 1-phosphate into UDP-galactose is rate-limiting in broken cell preparations, whereas the enzymatic 4-epimerization takes place at an appreciable rate. The latter reaction is strongly inhibited by reduced diphosphopyridine nucleotide, especially at a pH close to 7. In intact L cells and HeLa cells, UDP-galactose 4-epimerase is rate-limiting. The intracellular epimerase activity constitutes only about 0.1% of that found under optimal conditions in broken cells. Addition of galactose to these cells brings about a block between the general carbon pool of metabolites and the UDP-hexose pool. This is borne out by the fact that administration to intact L cells or to HeLa cells of 14 C-galactose and 12 C-glucose in equimolar amounts brings about incorporation by 14 C into UDP-hexose without detectable dilution of nonradioactive glucose. This blockage of the UDP-hexose pool from the general metabolic pool as well as the blockage of UDP-galactose 4-epimerase may have biological implications, some of which are briefly discussed.