Lipogenesis in rat and guinea-pig isolated epididymal fat-cells.
Fat-cells were prepared from rat and guinea-pig epididymal adipose tissue and compared on the basis of the intracellular distributions and activities of enzymes and with respect to their utilization of various U-(14)C-labelled substrates for lipogenesis. 1. Compared with the rat, guinea-pig extramitochondrial enzyme activities differed in that aconitate hydratase, alanine aminotransferase, ATP-citrate lyase, lactate dehydrogenase, NAD-malate dehydrogenase, NADP-malate dehydrogenase and phosphoenolpyruvate carboxykinase activities were appreciably lower, whereas aspartate aminotransferase, glucose 6-phosphate dehydrogenase, NADP-isocitrate dehydrogenase and 6-phosphogluconate dehydrogenase activities were appreciably higher. Mitochondrial activities of citrate synthase, NADP-isocitrate dehydrogenase and pyruvate carboxylase were appreciably lower, whereas mitochondrial activities of aspartate aminotransferase, glutamate dehydrogenase, NAD-malate dehydrogenase and phosphoenolpyruvate carboxykinase were higher in the guinea pig compared with the rat. 2. In general guinea-pig fat-cells incorporated acetate and lactate into fatty acids more readily than rat fat-cells, whereas rat fat-cells incorporated glucose and pyruvate more readily than guinea-pig fat-cells. 3. Acetate stimulated the incorporation of glucose into fatty acids in rat fat-cells, but had no appreciable effect upon this process in guinea-pig fat-cells. Acetate greatly decreased the incorporation of lactate into fatty acids in cells from both species. 4. Lactate/pyruvate ratios produced by incubation of guinea-pig cells with glucose+insulin were very low compared with those found with rat cells under the same conditions. 5. With glucose (+insulin) or with glucose+acetate (+insulin) as substrates guinea-pig cells produced enough NADPH by the hexose monophosphate pathway to satisfy the NADPH requirements of lipogenesis. In rat fat-cells under the same conditions, hexose monophosphate-pathway NADPH provision was not sufficient to meet the requirements of lipogenesis. 6. These results are discussed, particularly in relationship to the disposition of cytosolic reducing equivalents in the cells.
D001275:ATP Citrate (pro-S)-Lyase / Q000378:metabolism; D000085:Acetates / Q000378:metabolism; D000154:Aconitate Hydratase / Q000378:metabolism; D000273:Adipose Tissue / Q000201:enzymology / Q000378:metabolism*; D000410:Alanine Transaminase / Q000378:metabolism; D000818:Animals; D002250:Carbon Radioisotopes; D004822:Epididymis / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D006168:Guinea Pigs; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D008055:Lipids / Q000096:biosynthesis*; D008291:Malate Dehydrogenase / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009243:NAD; D009249:NADP; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism; D010734:Phosphogluconate Dehydrogenase / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism; D051381:Rats; D013053:Spectrophotometry
D000085:Acetates; D002250:Carbon Radioisotopes; D007773:Lactates; D008055:Lipids; D011773:Pyruvates; D009243:NAD; D009249:NADP; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase; D007521:Isocitrate Dehydrogenase; D010734:Phosphogluconate Dehydrogenase; D005954:Glucosephosphate Dehydrogenase; D001275:ATP Citrate (pro-S)-Lyase; D000410:Alanine Transaminase; D010729:Phosphoenolpyruvate Carboxykinase (GTP); D000154:Aconitate Hydratase; D005947:Glucose