Showing papers on "Phosphofructokinase activity published in 1979"

Phosphorus-31 nuclear magnetic resonance studies of wild-type and glycolytic pathway mutants of Saccharomyces cerevisiae.

Abstract: High-resolution phosphorus-31 nuclear magnetic resonance (31P NMR) spectra of wild-type and mutant strains of Saccharomyces cerevisiae were observed at a frequency of 145.7 MHz. Levels of various phosphorus metabolites were investigated upon addition of glucose under both aerobic and anaerobic conditions. Three mutant strains were isolated and their biochemical defects characterized: pfk lacked phosphofructokinase activity; pgi lacked phosphoglucose isomerase activity; and cif had no glucose catabolite repression of the fructose bisphosphatase activity. Each mutant strain was found to accumulate characteristic sugar phosphates when glucose was added to the cell suspension. In the case of the phosphofructokinase deficient mutant, the appearance of a pentose shunt metabolite was observed. 31P NMR peak assignments were made by a pH titration of the acid extract of the cells. Separate signals for terminal, penultimate, and central phosphorus atoms in intracellular polyphosphates allowed the estimation of their average molecular weight. Signals for glycero(3)phosphochline, glycero(3)phosphoserine, and glycero(3) phosphoethanolamine as well as three types of nucleotide diphosphate sugars could be observed. The intracellular pH in resting and anaerobic cells was in the range 6.5--6.8 and the level of adenosine 5'-triphosphate (ATP) low. Upon introduction of oxygen, the ATP level increased considerably and the intracellular pH reached a value of pH 7.2--7.3, irrespective of the external medium pH, indicating active proton transport in these cells. A new peak representing the inorganic phosphate of one of the cellular organelles, whose pH differed from the cytoplasmic pH, could be detected under appropriate conditions.

The Pasteur effect and catabolite repression in an oxidative yeast, Kluyveromyces lactis.

Abstract: The presence of the Pasteur effect in Kluyveromyces lactis grown in glucose was shown by azide-stimulated glucose fermentation. Extracts from these cells contained ATP-sensitive phosphofructokinase activity. Cells grown on succinate oxidized glucose slowly at first without azide-stimulated rates of fermentation. Phosphofructokinase in these cells was ATP-insensitive. The activity of NAD+-isocitrate dehydrogenase in cell extracts did not require AMP activation. These results suggested the presence of a Pasteur effect in glucose-grown but not in succinate-grown K. lactis, mediated by (a) ATP inhibition of phosphofructokinase (b) possibly via feedback control of glucose transport, but not by AMP activation of isocitrate dehydrogenase. Azide inhibition of the Pasteur effect during growth of the cells did not lead to catabolite repression of respiratory activity. The results therefore suggest that the Pasteur effect does not inhibit the development of a Crabtree effect in oxidative yeasts.

Phosphofructokinase Regulation in Some Transplantable Thyroid Tumors

Abstract: Some kinetic, molecular, and rate-limiting properties of partially purified phosphofructokinase from normal rat thyroid and three transplantable rat thyroid tumors have been studied, and interesting differences have been found. Citrate inhibition of tumor phosphofructokinase and its reversal by cyclic adenosine 3′:5′-monophosphate were lower than those of the normal enzyme. A direct relationship between tumor growth rate and the decrease of citrate inhibition was observed. The diethylaminoethyl cellulose affinity properties of the rat thyroid phosphofructokinase were slightly but consistently different from those of the three tumors; differences observed among the tumor enzymes with regard to these properties were likewise related to their respective growth rates. When the amounts of lactate, pyruvate, and glycerol 3-phosphate produced from each of the substrates of the glycolytic pathway were measured, it was found that, in contrast to results obtained with normal thyroid extracts, no rate-limiting function was associated with phosphofructokinase activity in tumor extracts. It was concluded that the modulation of phosphofructokinase by its allosteric effectors was similar in all three tumors, although different from that of the enzyme from normal rat thyroid; it was proportional to tumor growth rate and probably related to molecular and regulatory modifications.

Molecular properties of phosphofructokinase (pfk) relevant to modulation of its function

Abstract: Studies during the past twenty years on the molecular properties of phosphofructokinase have contributed immensely to our understanding of its role as an important regulatory enzyme in glycolysis Both covalent and non-covalent changes in enzyme structure have been reported Evidence has been accumulating showing variation in phosphofructokinase activity in connection with different physiological conditions In many cases the changes in enzyme activity is implied from indirect evidence and on the basis of what we already know of the properties of the enzyme We wish to summarize briefly our current knowledge of some of the most important molecular properties of the enzyme We will then report on some recent experiments on its allosteric sites and the nature of inhibition by vanadate Finally, we will discuss briefly the relationship between these properties and the regulatory function of phosphofructokinase