GLUTAMINE-METABOLISM IN AS-30D HEPATOMA-CELLS - EVIDENCE FOR ITS CONVERSION INTO LIPIDS VIA REDUCTIVE CARBOXYLATION

A study was undertaken to assess the role of a physiological concentra tion of glutamine in AS-30D cell metabolism. Flux of C-14-glutamine to (CO2)-C-14 and of C-14-acetate to glutamate was detected indicating r eversible flux between glutamate and TCA cycle alpha-ketoglutarate. Th ese fluxes were transaminase dependent. A flux analysis was compared u sing data from three tracers that label alpha-ketoglutarate carbon 5, [2-C-14]glucose, [1-C-14]acetate and [5-C-14]glutamine. The analysis i ndicated that the probability of flux of TCA cycle alpha-ketoglutarate to glutamate was, at minimum, only slightly less than the probability of flux of alpha-ketoglutarate through alpha-ketoglutarate dehydrogen ase. The apparent Km for oxidative flux of [C-14]glutamine to (CO2)-C- 14, 0.07 mM, indicated that this flux was at a maximal rate at physiol ogical, 0.75 mM, glutamine. Although oxidative flux through alpha-keto glutarate dehydrogenase was the major fate of glutamine, flux of gluta mine to lipid via reductive carboxylation of alpha-ketoglutarate was d emonstrated by measuring incorporation of [5-C-14]glutamine into C-14- lipid. In media containing glucose (6 mM), and glutamine (0.75 mM) 47 per cent of the lipid synthesized from substrates in the media was der ived from glutamine via reductive carboxylation and 49 per cent from g lucose. These findings of nearly equal fluxes suggest that lipogenesis via reductive carboxylation may be an important role of glutamine in hepatoma cells.