Cell volume changes affect gluconeogenesis in the perfused liver of the catfish Clarias batrachus.

In addition to lactate and pyruvate, some amino acids were found to serve as potential gluconeogenic substrates in the perfused liver of Clarias batrachus. Glutamate was found to be the most effective substrate, followed by lactate, pyruvate, serine, ornithine, proline, glutamine, glycine, and aspartate. Four gluconeogenic enzymes, namely phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase (PC), fructose 1,6-bisphosphatase (FBPase) and glucose 6-phosphatase (G6Pase) could be detected mainly in liver and kidney, suggesting that the latter are the two major organs responsible for gluconeogenic activity in this fish. Hypo-osmotically induced cell swelling caused a significant decrease of gluconeogenic efflux accompanied with significant decrease of activities of PEPCK, FBPase and G6Pase enzymes in the perfused liver. Opposing effects were seen in response to hyperosmotically induced cell shrinkage. These changes were partly blocked in the presence of cycloheximide, suggesting that the aniso-osmotic regulations of gluconeogenesis possibly occurs through an inverse regulation of enzyme proteins and/or a regulatory protein synthesis in this catfish. In conclusion, gluconeogenesis appears to play a vital role in C. batrachus in maintaining glucose homeostasis, which is influenced by cell volume changes possibly for proper energy supply under osmotic stress.

The limitations of paradigms: studies on the intermediary metabolism of Trypanosoma cruzi

We review the development of our knowledge and interpretations of the intermediary metabolism of Trypanosoma (Schizotrypanum) cruzi. Already in the 1950's it was clearly established that when this organism was exposed to large external concentrations of carbohydrates it was unable to catabolize them completely, even in the presence of oxygen, producing a mixture of CO2, dicarboxylic acids (succinic, malic) and alanine as end products. However, subsequent work tended to emphasize such paradigmatic features as a full complement of glycolytic enzymes in all stages of the life cycle of the parasite, a functional Kreb's cycle, a cytochrome-dependent electron transport chain and phosphorylative oxidation which suggested that T. cruzi had the basic metabolic properties of classical glucose-utilizing cells, in contrast with the degenerate glycolytic metabolism of bloodstream African trypanosomes. Only in the 1980's interest revived on the how and why of the incomplete carbohydrate catabolism by this parasite. The primary reason for this anomaly was found to be the presence of a constitutive phospho-enol-pyruvate carboxykinase (PEPCK, ATP-dependent, E.C.4.1.1.49), present in all stages of the parasite's life cycle, and the lack of regulation of the glycolytic route at its classical control points, hexokinase and phosphofructokinase. On the other hand, the presence of two distinct glutamate dehydrogenases (NAD+ and NADP(+)-dependent), the former being strictly regulated by the energy charge of the cell and the Krebs' cycle activity, indicated that amino acids can be a primary source of energy for this organism.(ABSTRACT TRUNCATED AT 250 WORDS)