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Biomedical subjects

V Macchia

Publications and source records attributed to V Macchia.

At least 55 records · Page 3Linked to original sources
PubMed1977

Phosphofructokinase (isozymes) activation by theophylline or by 3',5' cyclic AMP administration.

Phosphofructokinase activity of rat thyroid, kidney and muscle can be enhanced by in vivo administration of theophylline or cyclic AMP. This enhancement occurs in the different tissues to a different extent depending on the tissue-specific isozymes. Thyroid and muscle phosphofructokinase which is mainly A-type, is strongly stimulated after administering theophylline in the drinking water over a 8 days period. The kidney enzyme which encompasses about 50% of each A and B type is activated to a lesser extent. Liver phosphofructokinase which is pure B-type shows very little response if any. Comparable results have been obtained with either the muscle or liver enzyme after two to four hours treatment with a single injection of 10 mg/rat of either cyclic AMP or theophylline. This short-term activation could be eliminated by treating the animals with Actinomycin D, 30 min prior to theophylline or cyclic AMP. The possible mechanisms leading to the enhancement of phosphofructokinase activity are discussed.

Animals↗
PubMed1977

[Guanyl cyclase activity in the EF-T elongation factor of Escherichia coli].

Highly purified EF-Ts from E. coli does contain guanylate cyclase activity, which is absent from other purified transfer factors, such as EF-Tu and EF-G. Guanylate cyclase activity has been characterized by its sensitivity to inhibitors and substrate specificity. Although the physicochemical properties of guanylate cyclase are closely related to those of EF-Ts, it does not appear to be a contaminant of this transfer factor, but a specific enzyme. The possible role of guanylate cyclase in protein synthesis is discussed.

Aurintricarboxylic Acid↗
PubMed1976

Differences in phosphofructokinase regulation in normal and tumor rat thyroid cells.

The kinetic and molecular properties of a phosphofructokinase derived from a transplantable rat thyroid tumor lacking regulatory control on the glycolytic pathway were studied. The properties of the near-purified enzyme (specific activity 140 units/mg) were compared with those of phosphofructokinase from normal rat thyroid (specific activity 134 units/mg). The electrophoretic mobilities and gel elution behavior of these two enzymes were almost similar. The thyroid tumor phosphofructokinase showed, however, a greater degree of size and/or shape heterogeneity in the presence of ATP than the normal thyroid enzyme, as determined by gel filtration and sucrose density gradient centrifugation. Kinetic studies below pH 7.4 showed a sigmoid response curve for both enzymes when the velocity was determined at 1 mM ATP with varying levels of fructose-6-P. The interaction coefficient, however, was 4.2 and 2.6 for normal and tumor thyroid phosphofructokinase, respectively. Ammonium sulfate decreased the cooperative interactions with the substrate fructose-6-P in both enzymes. The thyroid tumor enzyme, however, was less sensitive to the inhibition by ATP and by citrate. The reversal of citrate inhibition by cyclic 3':5'-adenosine monophosphate was also less effective with the thyroid tumor phosphofructokinase, while the protective effect of fructose-6-P was stronger. The difference in citrate inhibition between tumor and normal thyroid enzyme was not strongly affected by varying the MgCl2 concentration up to 10 mM. It is concluded that the complex allosteric regulation typical of the normal thyroid phosphofructokinase is still present in the enzyme isolated from the thyroid tumor tissue. The latter, however, is more loosely controlled by its physiological effectors, such as ATP, citrate, and cyclic AMP.

Adenosine Triphosphate↗
PubMed1975

Guanylate cyclase in Escherichia coli. Purification and properties.

Guanylate cyclase has been purified from extracts of Escherichia coli. After a 1000-fold purification, the enzyme contains only minor contaminants as judged by disc gel electrophoresis. The Km for GTP is approximately 7 times 10(-5) M and the optimal pH is 8.0. More activity is observed with Mn2+ than with Mg2+, and maximal activity is observed at 0.14 mM Mn2+ and 1.4 mM Mg2+. Based on its behavior on Sephadex G-100, the molecular weight of E. coli guanylate cyclase is about 30,000. Disc gel electrophoretic analysis indicates that the enzyme consists of a single polypeptide chain. Guanylate cyclase does not form 3':5'-AMP from ATP, and therefore, is distinct from adenylate cyclase.

Enzyme Activation↗
PubMed1975

Diminished binding of thyroid-stimulating hormone in a transplantable rat thyroid tumor as a possible cause of hormone unresponsiveness.

The adenylate cyclase activity and the binding of 125I-labeled thyroid-stimulating hormone (TSH) of normal and tumor rat thyroid plasma membranes were compared. No significant difference in the basal and fluoride-sensitive adenylate cyclase activity between normal and tumor plasma membranes was observed. Thyroid plasma membranes responded to TSH, whereas the enzyme from the tumor plasma membranes was TSH insensitive. Thyroid plasma membranes boud 125I-TSH. Tumor plasma membranes bound 125I-TSH poorly. At the highest concentration of unlabeled TSH used, 80% of the 125I-TSH that was bound to thyroid plasma membranes was displaced, whereas only 10% of the 125I-TSH bound to tumor plasma membranes was displaced. Therefore, it seems likely that the failure of this tumor to respond to TSH is due to an alteration in the functional unit of membrane adenylate cyclase at the level of the receptor subunit.

Adenylyl Cyclases↗
PubMed1975

[Subcellular distribution of the protein kinase activity in the normal and neoplastic thyroid tissue of the rat].

Thyroid tissue has been fractionnated by centrifugation (105 000 q) of its homogenate. Protein-kinase activity in presence of histone is distributed in nuclei (11.5%) mitochondira (22.8%), microsomes (9.8%) and soluble fraction (56%); it is activated by cyclic AMP and GMP, mostly in soluble and nuclear fractions. Protein-kinase activity of total homogenate of neoplasic thyroid (strain 1-5G Wollman) in presence of histone is 3 times higher than in normal tissue and more activated by cAMP. In absence of histone, protein-kinase activity is the more important in mitochondrial and microsomal fractions of normal thyroid and in soluble and nuclear fraction of neoplastic tissue.

Animals↗
PubMed1975

[Presence of various protein kinases and of partially copurified endogenous substrates in the soluble fraction of an experimental tumor of the rat thyroid gland].

Various fractions containing protein-kinases have been partly purified from supernatant (105 000 g) of an experimental rat's thyroid cancer (1-8 Wollman). These fractions are activated at different levels by cyclic nucleotides and present an unequal affinity for protamine; they phosphorylate an endogenous substrate apparently copurified with the enzyme fractions and adorbed with them on calcium phosphate gel.

Animals↗
PubMed1970

The effect of a purified preparation of lecithinase C on iodide transport.

Treatment of porcine thyroid slices with highly purified lecithinase C leads to a marked reduction in the ability to accumulate iodide ion. Although this response is less sensitive as a function of lecithinase concentration than is the ability to respond to thyrotropin with an increase in glucose oxidation, phospholipid synthesis or adenyl cyclase activity, it occurs when the baseline values of these parameters are not substantially altered.

Journal Article↗