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PubMed1981

Red cell metabolic alterations in postnatal life in term infants: glycolytic intermediates and adenosine triphosphate.

Red cell glycolytic intermediates and adenosinetriphosphate were evaluated in term infants from birth to on year of age and compared to values obtained from normal adults and subjects wit a population of a similar mean cell age. The concentration of glycolytic intermediates, with the exception of phosphoenolypyruvate were elevated at birth when compared to normal subjects, consistent with a young mean red cell population. The mean levels of red cell glucose-6-phosphate, fructose-6-phosphate, and "total triose phosphate" were elevated on days 1 and 4 of life when compared to both red cells from normal adults and subjects with a similar young mean red cell age. Glucose-6-phosphate steadily increased in concentration, peaked at 3 to 4 wk of age, and then progressively decreased in value. Total triose phosphate declined to a mildly elevated concentration by 3 to 4 wk of age. The mean concentrations of 2,3-diphosphoglycerate and adenosine triphosphate were normal on day 1, increased on day 4, and then declined by 3 to 4 wk to normal values, until 5 to 6 months when both increased. The mean phosphoenolpyruvate concentration was decreased on day 1 of age when compared to red cells of a similar mean age, but this decrease was not significant (P greater than 0.05). The mean concentrations of 3-phosphoglycerate increased at 3 to 4 wk of age and remained elevated for cell age at 11 to 12 months but this increase was no statistically significant (P greater than 0.05). 3-Phosphoglycerate levels did not change significantly throughout the first year of life. At one year of age, all red glycolytic intermediates and adenosine triphosphate were elevated when compared to red cells from normal adults, but were comparable to those observed in subjects with a red cell population of a similar mean cell age, consistent with the persistence of a young red cell population throughout the first year of life.

Adenosine Triphosphate↗
PubMed2002

Glucose metabolites inhibit protein phosphatases and directly promote insulin exocytosis in pancreatic beta-cells.

In human type 2 diabetes mellitus, loss of glucose-sensitive insulin secretion is an early pathogenetic event. Glucose is the cardinal physiological stimulator of insulin secretion from the pancreatic beta-cell, but the mechanisms involved in glucose sensing are not fully understood. Specific ser/thr protein phosphatase (PPase) inactivation by okadaic acid promotes Ca(2+) entry and insulin exocytosis in the beta-cell. We now show that glycolytic and Krebs cycle intermediates, whose concentrations increase upon glucose stimulation, not only dose dependently inhibit ser/thr PPase enzymatic activities, but also directly promote insulin exocytosis from permeabilized beta-cells. Thus, fructose-1,6-bisphosphate, phosphoenolpyruvate, 3-phosphoglycerate, citrate, and oxaloacetate inhibit PPases and significantly enhance insulin exocytosis, nonadditive to that of okadaic acid, at micromolar Ca2+ concentrations. In contrast, the effect of GTP is potentiated by okadaic acid, suggesting that the action of GTP does not require PPase inactivation. We conclude that specific glucose metabolites and GTP inhibit beta-cell PPase activities and directly stimulate Ca2+-independent insulin exocytosis. The glucose metabolites, but not GTP, seem to require PPase inactivation for their stimulatory effect on exocytosis. Thus, an increase in phosphorylation state, through inhibition of protein dephosphorylation by metabolic intermediates, may be a novel regulatory mechanism linking glucose sensing to insulin exocytosis in the beta-cell.

Animals↗
PubMed1988

Fructose 2,6-bisphosphate and glycolytic oscillations in skeletal muscle extracts.

Oscillatory behavior of glycolysis in cell-free extracts of rat skeletal muscle involves bursts of phosphofructokinase activity due to autocatalytic activation by fructose-1,6-P2. Fructose-2,6-P2 is an even more potent activator of phosphofructokinase and is competitive with fructose-1,6-P2 in binding and kinetic studies. The possible role and effects of fructose-2,6-P2 on the oscillating system were therefore examined. When muscle extracts were provided with 1 mM ATP and 10 mM glucose, fructose-2,6-P2 slowly accumulated to 50 nM in 1 h. The nearly monotonic rise, in contrast to the 50-fold oscillations in fructose-1,6-P2, indicated no involvement of fructose-2,6-P2 in the oscillatory process. Addition of 0.5 microM fructose-2,6-P2 blocked the oscillations, and there was negligible appearance of glycolytic intermediates from fructose-1,6-P2 to phosphoenolpyruvate, although similar amounts of lactate accumulated. In the presence of 0.2 microM fructose-2,6-P2, there were small, transient accumulations of fructose-1,6-P2, suggesting aborted activations of phosphofructokinase. Oscillations were not blocked by 0.1 microM fructose-2,6-P2. The average [ATP]/[ADP] ratio in the presence of 0.2 or 0.5 microM fructose-2,6-P2 was half the value in its absence, demonstrating the advantage of the oscillatory behavior in maintaining a high energy state. In the presence of higher, near physiological levels of ATP and citrate, inhibitors which reduce the affinity of phosphofructokinase for fructose-2,6-P2, glycolytic oscillations were not blocked by 1 microM fructose-2,6-P2, its approximate concentration in vivo.

Animals↗
PubMed1994

Allosteric sites of the large subunit of the spinach leaf ADPglucose pyrophosphorylase.

Pyridoxal-P, an analog of 3-phosphoglycerate, activates spinach leaf ADPglucose pyrophosphorylase. Reductive phosphopyridoxylation of the enzyme yields enzyme less dependent on the presence of activator for activity. Labeled pyridoxal-P is incorporated into both the 51- and 54-kDa subunits of the enzyme. The sequence of the single tryptic labeled peptide of the small subunit has been reported (Morell, M., Bloom, M., and Preiss, J. (1988) J. Biol. Chem. 263, 633-637). Three distinct labeled peptides are isolated from the tryptic digest of the large subunit. 3-Phosphoglycerate inhibits incorporation of pyridoxal-P by 80% into all three large subunit tryptic peptides, whereas inorganic phosphate, the allosteric inhibitor, inhibits incorporation into only one of those peptides. Comparison of the sequences of the labeled tryptic peptides with those of large and small subunits of the enzyme from other species indicate their positions in the primary structure of the spinach enzyme large subunit. The conservation in the amino acid sequences surrounding the lysyl residue in the small subunit and of the lysyl residue in the large subunit in higher plant and in cyanobacterial ADPglucose pyrophosphorylases, which are protected from phosphopyridoxylation by both allosteric effectors, suggests that these lysyl residues are involved in activator binding.

Allosteric Regulation↗
PubMed2006

ATP binding site in the plant ADP-glucose pyrophosphorylase large subunit.

The ATP binding region in the catalytically inactive large subunit (LS) of the potato tuber ADP-glucose pyrophosphorylase was identified and investigated. Mutations at the ATP binding significantly affected not only the apparent affinities for ATP and Glc-1-P, and catalytic rate but also in many instances, sensitivity to 3-phosphoglycerate. The catalytic rates of the LS mutant enzymes correlated most strongly with changes in the affinity toward ATP, a relationship substantiated by photoaffinity labeling studies with azido-ATP analog. These results indicate that the LS, although catalytically defective, interacts cooperatively with the catalytic small subunit in binding substrates and effectors and, in turn, influencing net catalysis.

Adenosine Triphosphate↗
PubMed1975

Aerobic adaptation in yeast. I. Changes in metabolic intermediates during a step-down anaerobic-aerobic transfer.

Early investigation into the mechanism of mitochondriogenesis in the facultative anaerobe Saccharomyces cerevisiae used anaerobic-aerobic transitions as model systems to study the in vivo assembly of these oxidative organelles. This methodology has become entrenched in the early literature and as a result a definitive study has been undertaken utilizing this protocol (high hexose, complete medium under anaerobic growth transferred to low hexose, minimal medium with aerobic environment) to study the altered distribution of various metabolites during these transitions. Measurement of all the glycolytic, and some tricarboxylic acid intermediates during such a transition has elucidated the following points. On a qualitative basis, the metabolic controls prevalent in these growing cultures are similar to those identified in yeast under less physiological conditions. Also, the effect of anaerobic catabolism, which preconditions enzyme and pool levels in the yeast, is of paramount importance in determining the events subsequent to oxygen challenge. However, this experimental approach has severe limitations and does not lend itself to a clear-cut delineation of the events that occur during the process of mitochondriogenesis.

Adenosine Triphosphate↗
PubMed1976

Carbohydrate metabolism in perfused livers of adrenalectomized and steroid-replaced rats.

In livers from fasted rats perfused with bicarbonate buffer containing bovine albumin and erythrocytes, adrenalectomy decreased glycogen levels and glucose production, impaired the incorporation of 14C from [14C]lactate into glucose or glycogen, and decreased the activity of the active (I) form of glycogen synthase. Cortisol treatment restored gluconeogenesis after 1 h and glycogen synthesis after 2 h. Adrenalectomy did not alter the production of glucose or lactate or the levels of gluconeogenic intermediates in livers from fasted rats perfused with fructose, but reduced the formation of glycogen from this substrate. Adrenalectomy increased the levels of lactate and decreased the levels of P-pyruvate and subsequent intermediates in the gluconeogenic pathway. These changes were reversed by cortisol treatment. It is concluded that glucocorticoids support gluconeogenesis and glycogen synthesis in livers from fasted rats primarily by facilitating a reaction(s) located between pyruvate and P-pyruvate in the gluconeogenic pathway and by promoting the conversion of inactive to active glycogen synthase.

Adenosine Diphosphate↗
PubMed1985

Red cell glycolytic intermediates and adenosine triphosphate in preterm infants on the first day of life.

Red cell glycolytic intermediates and ATP were evaluated in 47 appropriate for gestational age preterm infants on the 1st day of life who were divided into three groups on the basis of gestational age: 28-30, 31-33, and 34-36 wk. The results were compared to those previously obtained in term infants. The concentrations of glucose-6-phosphate, total triose phosphates, and ATP were significantly higher than in term infants but appeared to be appropriately elevated for the young mean age of the red cell population. The concentration of red cell 2,3-diphosphoglycerate (2,3-DPG) was significantly decreased when compared to term infants and was lowest at 28-30 wk gestation. The content of red cell 3-phosphoglycerate was increased in term infants and was inappropriately elevated for the age of the red cell population at 28-30 wk gestation. This pattern of glycolytic intermediates was suggestive of a young red cell population metabolizing at an increased glycolytic rate with increased flow through the phosphoglycerate kinase step rather than the 2,3-DPG bypass in "normal" preterm infants. Two preterm infants of 28-30 wk gestation with low red cell intracellular pH were also evaluated and had markedly decreased concentrations of red cell 2,3-DPG and ATP and all phosphorylated intermediates distal to the phosphofructokinase reaction, indicative of a cross-over at the phosphofructokinase step secondary to acidosis.(ABSTRACT TRUNCATED AT 250 WORDS)

2,3-Diphosphoglycerate↗