Regulation of flux through pyruvate dehydrogenase and pyruvate carboxylase in rat hepatocytes: effects of fatty acids and glucagon
L Agius, KGMM Alberti - European journal of biochemistry, 1985 - Wiley Online Library
L Agius, KGMM Alberti
European journal of biochemistry, 1985•Wiley Online Library1 The regulation of flux through pyruvate dehydrogenase (PDH) and pyruvate carboxylase
(PC) by fatty acids and glucagon was studied in situ, in intact hepatocyte suspensions. 2 The
rate of pyruvate metabolized by carboxylation plus decarboxylation was determined from the
incorporation of [1‐14C] pyruvate into 14CO2 plus [14C] glucose. The flux through PDH was
determined from the rate of formation of 14CO2 from [1‐14C] pyruvate correted for other
decarboxylation reactions (citrate cycle, phosphoenolpyruvate carboxykinase and malic …
(PC) by fatty acids and glucagon was studied in situ, in intact hepatocyte suspensions. 2 The
rate of pyruvate metabolized by carboxylation plus decarboxylation was determined from the
incorporation of [1‐14C] pyruvate into 14CO2 plus [14C] glucose. The flux through PDH was
determined from the rate of formation of 14CO2 from [1‐14C] pyruvate correted for other
decarboxylation reactions (citrate cycle, phosphoenolpyruvate carboxykinase and malic …
- 1The regulation of flux through pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) by fatty acids and glucagon was studied in situ, in intact hepatocyte suspensions.
- 2The rate of pyruvate metabolized by carboxylation plus decarboxylation was determined from the incorporation of [1‐14C]pyruvate into 14CO2 plus [14C]glucose. The flux through PDH was determined from the rate of formation of 14CO2 from [1‐14C]pyruvate correted for other decarboxylation reactions (citrate cycle, phosphoenolpyruvate carboxykinase and malic enzyme), and the flux through PC was determined by substracting the flux through PDH from the total pyruvate metabolized.
- 3With 0.5 mM pyruvate as substrate the ratio of flux through PDH/PC was 1.9 in hepatocytes from fed rats and 1.4 in hepatocytes from 24 h‐starved rats.
- 4In hepatocytes from fed rats, octanoate (0.8 mM) and palmitate (0.5 mM) increased the flux through PDH (59–76%) and PC (80–83%) without altering the PDH/PC flux ratios. Glucagon did not affect the flux through PDH but it increased the flux through PC twofold, thereby decreasing the PDH/PC flux ratio to the value of hepatocytes from starved rats.
- 5In hepatocytes from starved rats, fatty acids had similar effects on pyruvate metabolism as in hepatocytes from fed rats, however glucagon did not increase the flux through PC.
- 62[5(4‐Chlorophenyl)pentyl]oxirane‐2‐carboxylate (100 μM) an inhibitor of carnitine palmitoyl transferase I, reversed the palmitate‐stimulated but not the octanoate‐stimulated flux through PDH, in cells from fed rats, indicating that the effects of fatty acids on PDH are secondary to the β‐oxidation of fatty acids. This inhibitor also reversed the stimulatory effect of palmitate on PC and partially inhibited the flux through PC in the presence of octanoate suggesting an effect of POCA independent of fatty acid oxidation.
- 7It is concluded that the effect of fatty acids on pyruvate metabolism are probably secondary to increased pyruvate uptake by mitochondria in exchange for acetoacetate. Glucagon favours the partitioning of pyruvate towards carboxylation, by increasing the flux through pyruvate carboxylase, without directly inhibiting the flux through PDH.
Wiley Online Library