Lipogenic activities in rat liver are subjected to circadian rhythms.

Diurnal variations were investigated in the activities of the key lipogenic enzymes in rat liver under standard experimental conditions. Fatty acid synthetase, acetyl-CoA-carboxylase, and ATP-citrate lyase showed sinusoidal circadian rhythms (statistically sustained), reaching maximum activity at night and minimum during the light period, with a fold increase value of 1.7, 2.2 and 3.2, respectively. Although a non-sinusoidal circadian rhythm was observed in the malic enzyme activity, statistically different time-dependent activity values were detected throughout a day. The observed rhythms run in parallel with that previously reported for glucose-6-phosphate dehydrogenase, suggesting a whole circadian regulation for rat liver lipogenesis.

Metabolic regulation of glycolysis in sea bass (Dicentrarchus labrax L.) muscle. I. Kinetic study and characteristic modulators of pyruvate kinase.

White muscle pyruvate kinase from sea bass presents positive cooperativity with respect to PEP substrate. The enzyme is regulated by F-1.6-P2 and L-Phenylalanine. The activator effect of F-1.6-P2 in experiments carried out for the substrate PEP with crude extract seems to indicate that the enzyme is activated in vivo by this compound. The enzyme was not inhibited by either alanine or ATP but was inhibited by L-phenylalanine. Therefore this enzyme presents kinetic and regulatory properties similar to those of the mammalian isozyme M2.