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Biomedical subjects

S Pontremoli

Publications and source records attributed to S Pontremoli.

At least 163 records · Page 9Linked to original sources
PubMed1979

Changes in activity of fructose-1,6-bisphosphate aldolase in livers of fasted rabbits and accumulation of crossreacting immune material.

The activity of fructose-1,6-bisphosphate aldolase (D-fructose-1,6-bisphosphate D-glyceraldehyde-3-phosphate-lyase, EC 4.1.2.13) in livers of fasted rabbits decreases to less than one-half the value found in livers of fed rabbits. However, the concentration of aldolase protein in the liver extracts, measured with a specific antibody, remains unchanged. More than twice as much antibody is required to neutralize the aldolase activity in liver extracts from fasted compared with fed rabbits. The results suggest that modification of liver aldolase occurs during fasting, resulting in loss of catalytic activity without loss of immunoreactivity.

Animals↗
PubMed1977

Binding of Zn2+ to rat liver fructose-1,6-bisphosphatase and its effect on the catalytic properties.

Rat liver fructose-1,6-bisphosphatase (D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) contains 12 binding sites for Zn2+ per molecule, or 3 per subunit, as determined by gel filtration and by precipitation of an insoluble Zn2+-enzyme complex. The first set of sites binds Zn2+ with very high affinity, and the binding constant for these sites could not be determined. The average values of the dissociation constants for the second and third sets of sites were approximately 0.4 and 1.5 muM, respectively. The third set of sites, having lowest affinity, appears to be identical to the binding sites for the activating cation, Mg2+, and the binding of Zn2+ to this set of sites is prevented by the addition of Mg2+. Binding of the first 4 equivalents of Zn2+ yields an enzyme of intermediate activity, while the binding of 8 equivalent results in almost complete inhibition of catalytic activity. Thus Zn2+ appears to function as both an activator and a negative allosteric regulator of fructose-1,6-bisphosphatase activity.

Allosteric Site↗
PubMed1976

Evidence for the selective release of lysosomal proteinases in fasted rabbits.

The enzyme responsible for the conversion of "neutral" to "alkaline" fructose 1,6-bisphosphatase (EC 3.1.3.11) by removal of a 7000 dalton peptide (converting enzyme, Proteinase I) has been shown to be localized in rat liverlysosomes. Lysosomes also contain a specific proteinase (Proteinase II) that catalyzes the release of a small peptide from the NH2-terminus of the native subunits. In fasted rabbits Proteinase II is released into the cytoplasm, together with Cathepsin A, but Proteinase I remains associated with the lysosomal fraction. Increased osmotic fragility of liver lysosomes in fasted rabbits has also been observed, but this increased fragility does not result in the release of Proteinase I. The appearance of Proteinase II in the cytoplasm may be due either to its selective release from the lysosomes, without release of Proteinase I, or its localization in a different lysosomal fraction. Changes in lysosomal structure induced by fasting may play a dual role in : 1) the mobilization of amino acids for gluconeogenesis and 2) the modulation of activity of gluconeogenic enzymes.

Acid Phosphatase↗
PubMed1976

Dual role of Zn2+ as inhibitor and activator of fructose 1,6-bisphosphatase of rat liver.

At neutral pH, Zn2+ is a potent and specific inhibitor of rat liver fructose 1,6-bisphosphatase (EC 3.1.3.11; D-fructose-1,6-bisphosphate 1-phosphohydrolase). Inhibition by Zn2+ is uncompetitive with respect to the activating cations Mg2+ and Mn2+, and the kinetic data suggest that the enzyme possesses a distinct high-affinity binding site for Zn2+, with Ki of approximately 0.3 muM. At higher concentrations (about 10(-5) M) Zn2+, and to a lesser extent Co2+, function as activating cations. Binding studies show that the enzyme binds two equivalents of Zn2+ per subunit; one equivalent is partially displaced by Mg2+ and is presumably bound to the site for activating cations. A second equivalent binds to the high-affinity site, presumably identical to the inhibitory site. The results suggest that Zn2+ functions as an allosteric regulator, and that the commonly observed activation of fructose 1,6-bisphosphatase at neutral pH by EDTA, histidine, and other chelators is due to removal of endogenous Zn2+ by these agents.

Animals↗
PubMed1975

Hormonal effects on structure and catalytic properties of fructose 1,6-bisphosphatase.

Gluconeogenic conditions, such as administration of triamcinolone or alloxan diabetes, cause the following changes in the molecular structure and properties of rabbit liver fructose 1,6-bisphosphatase (D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11): (1) the appearance of traces (about 10%) of a lighter subunit; (2) loss of tryptophan from all of the subunits, including those that show no apparent change in molecular weight; (3) increase in requirement for the positive allosteric effector, histidine; (4) increase in amount of enzyme, but not its specific activity. These changes are identical to those induced by cold or fasting, and are related to increased activities of lysosomal proteases. The results suggest that lysosomes may act as mediators of gluconeogenic stimuli.

Amino Acids↗