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M Camici

Publications and source records attributed to M Camici.

34 records · Page 2Linked to original sources
PubMed1989

[Membrane signals: role of the inositol phosphate system].

Current information on cellular communications through plasmatic or synaptic mediators raises a great deal of questions about intracellular messengers diffusion and the apparent difference between the large number of intercellular mediators, or first messengers, and the few number of intracellular mediators, or second messengers. Regarding the intracellular messengers, the research is currently focused on the inositol phosphate system and especially on inositol-1,4,5 trisphosphate (IP3), which derives from the hydrolysis of a cellular membrane phosphoinositide: one of the most important function of IP3 is the release of intracellular calcium from the endoplasmic reticulum. The cell wall plays an important role in intracellular and intercellular communication as is shown by the balance between the cell-membrane phosphoinositide group and IP3 availability. Recent developments in knowledge about this inositol-phosphate system is going to show a new way of explanatory possibility about some not evident pathologies until now. The latest discovery of a specific intracellular receptor site of IP3 and the fact that some oligoelements, such as lithium, interfere with IP3 metabolism suggest exciting prospects for the treatment of pathologies resulting from these changes in receptor mechanism.

Chemical Phenomena↗
PubMed1989

Heparin and prostacyclin.

Hemodialysis performed with prostacyclin (5 ng/kg/min) as a substitute for heparin was studied in 10 patients. The subjects were studied during heparin perfusion alone and during heparin perfusion together with prostacyclin. The authors investigated the effect of two heparin regimens (regimen I: 2,000 U/hr and regimen II: 500 U/hr) upon plasma antithrombin level (IU/mL) and activated thromboplastin time (sec). Our findings show: (1) prostacyclin can substitute for heparin anticoagulation in hemodialysis; (2) the concomitant administration of prostacyclin enhances the anticoagulant effect of heparin, based on the measurement of the activated partial thromboplastin time; (3) the antithrombin activity is increased by both treatments but more so with prostacyclin; and (4) platelet activation plays a role in limiting heparin anticoagulation, a conclusion partly supported by the finding that activated partial thromboplastin time is somewhat more prolonged by heparin when measured in platelet-poor rather than in platelet-rich plasma in the presence of prostacyclin. Physiopathologic implications of these preliminary findings are discussed.

Adult↗
PubMed1988

Alpha-5-phosphoribosyl-1-pyrophosphate-independent salvage of purines in cultured Chinese hamster lung fibroblasts.

A variant clone of cultured chinese hamster lung fibroblasts (V79), selected for resistance to 8-azaguanine (V79 azagrst), although lacking hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), is able to convert hypoxanthine into IMP via purine-nucleoside phosphorylase (EC 2.4.2.1) and nucleoside kinase. In addition to the phosphoribosylation pathway, we also present evidence for the occurrence of a kinase-mediated pathway of recovery of hypoxanthine in the wild-type cells. The lower rate of formation of IMP in the V79 azagrst cells, apparently correlated with the phosphorylation of the nucleoside, suggests possible differences in the catalytic and/or regulatory properties of nucleoside kinase in the two cell lines. This fact might be of particular relevance in evaluating the mechanisms of resistance to purine analogs displayed by several cell types.

Animals↗
PubMed1987

Radioenzymatic determination of adenosine.

Adenosine has been measured at the nanomolar level by an enzymatic radioactive assay. The nucleoside is converted into [U-14C]ribose-labeled inosine via the following reactions: adenosine + H2O----adenine + ribose (adenosine nucleosidase); adenine + [U-14C]ribose 1-phosphate in equilibrium with T[U-14C]ribose-adenosine + Pi (adenosine phosphorylase); [U-14C]ribose-adenosine + H2O----[U-14C]ribose-inosine + NH3 (adenosine deaminase). The radioactivity of inosine, separated by thin-layer chromatography, is a measure of the adenosine initially present.

Adenosine↗
PubMed1987

In vitro modification of bovine lens aldose reductase activity.

Bovine lens aldose reductase can be activated in crude extracts upon incubation at 37 degrees C at relatively high ionic strength. This phenomenon shows a seasonal occurrence, the enzyme being susceptible to activation only in lenses of animals sacrified in summer. Systems generating oxygen activated species induce the enzyme activation, whereas scavengers of "oxygen radicals" preserve the activated state of the enzyme. Glutathione and other thiol compounds appear to prevent the enzyme activation.

Aldehyde Reductase↗
PubMed1987

A coupled optical assay for adenine phosphoribosyltransferase and its extension for the spectrophotometric and radioenzymatic determination of 5-phosphoribosyl-1-pyrophosphate in mixtures and in tissue extracts.

A reliable assay was developed to characterize crude cell homogenates with regard to their adenine phosphoribosyltransferase activities. The 5-phosphoribosyl-1-pyrophosphate (PRPP)-dependent formation of AMP from adenine is followed spectrophotometrically at 265 nm by coupling it with the following two-stage enzymatic conversion: AMP + H2O----adenosine + Pi (5'-nucleotidase); adenosine + H2O----inosine + NH3 (adenosine deaminase). The same principle was applied to develop a spectrophotometric and a radioenzymatic assay for PRPP. The basis of the spectrophotometric assay is the absorbance change at 265 nm associated with the enzymatic conversion of PRPP into inosine, catalyzed by the sequential action of partially purified adenine phosphoribosyltransferase, commercial 5'-nucleotidase, and commercial adenosine deaminase, in the presence of excess adenine. In the radiochemical assay PRPP is quantitatively converted into [14C]inosine via the same combined reaction. Tissue extracts are incubated with excess [14C]adenine. The radioactivity of inosine, separated by a thin-layer chromatographic system, is a measure of PRPP present in tissue extracts. The radioenzymatic assay is at least as sensitive as other methods based on the use of adenine phosphoribosyltransferase. However, it overcomes the reversibility of the reaction and the need to use transferase preparations free of any phosphatase and adenosine deaminase activities.

Adenine Phosphoribosyltransferase↗
PubMed1987

Phosphorylase-mediated mobilization of the amino group of adenine in Bacillus cereus.

Mobilization of the ribose moiety of purine nucleosides as well as of the amino group of adenine may be realized in Bacillus cereus by the concerted action of three enzymes: adenosine phosphorylase, adenosine deaminase, and purine nucleoside phosphorylase. In this pathway, ribose-1-phosphate and inorganic phosphate act catalytically, being continuously regenerated by purine nucleoside phosphorylase and adenosine phosphorylase, respectively. As a result of such a metabolic pathway, adenine is quantitatively converted into hypoxanthine, thus overcoming the lack of adenase in B. cereus.

Adenine↗
PubMed1986

Multiple phosphorylation sites of rat liver glycogen synthase.

Rat liver glycogen synthase was purified to homogeneity by an improved procedure that yielded enzyme almost exclusively as a polypeptide of Mr 85,000. The phosphorylation of this enzyme by eight protein kinases was analyzed by cleavage of the enzyme subunit followed by mapping of the phosphopeptides using polyacrylamide gel electrophoresis in the presence of SDS, reverse-phase high-performance liquid chromatography and thin-layer electrophoresis. Cyclic AMP-dependent protein kinase, phosphorylase kinase, protein kinase C and the calmodulin-dependent protein kinase all phosphorylated the same small peptide (approx. 20 amino acids) located in a 14 kDa CNBr-fragment (CB-1). Calmodulin-dependent protein kinase and protein kinase C also modified second sites in CB-1. A larger CNBr-fragment (CB-2) of approx. 28 kDa was the dominant site of action for casein kinases I and II, FA/GSK-3 and the heparin-activated protein kinase. The sites modified were all localized in a 14 kDa species generated by trypsin digestion. Further proteolysis with V8 proteinase indicated that FA/GSK-3 and the heparin-activated enzyme recognized the same smaller peptide within CB-2, which may also be phosphorylated by casein kinase 1. Casein kinase 1 also modified a distinct peptide, as did casein kinase II. The results lead us to suggest homology to the muscle enzyme with regard to CB-1 phosphorylation and the region recognized by FA/GSK-3, which in rabbit muscle is characterized by a high density of proline and serine residues. A striking difference with the muscle isozyme is the apparent lack of phosphorylations corresponding to the muscle sites 1a and 1b. These results provide further evidence for the presence of liver- and muscle-specific glycogen synthase isozymes in the rat. That the isozymes differ subtly as to phosphorylation sites may provide a clue to the functional differences between the isozymes.

Animals↗
PubMed1986

Concanavalin A induced inhibition of 5'-nucleotidase from guinea pig skeletal muscle and bull seminal plasma: a comparative study.

Both purified and membrane-bound 5'-nucleotidases (EC 3.1,3.5) from guinea pig skeletal muscle and bull seminal plasma are inhibited by Concanavalin A (Con A). 5'-Nucleotidase purified from skeletal muscle is inhibited by Con A by an apparent uncompetitive process (K'i = 160 nM), while the lectin inhibits the particulate enzyme by an apparent non-competitive process (Ki = K'i = 50 nM). 5'-Nucleotidase purified from bull seminal plasma is inhibited by Con A by an apparent non-competitive process (K'i = Ki = 270 nM), while the membrane-bound enzyme is subjected to a mixed type inhibition by the lectin (K'i greater than Ki; 30 and 14 nM, respectively). The enzyme purified from skeletal muscle exhibits a significant cooperativity in the interaction with Con A. The inhibition of bull seminal plasma particulate 5'-nucleotidase brought about by Con A is not completely reversed by addition of alpha-methyl-D-mannoside.

5'-Nucleotidase↗
PubMed1985

Isolation and kinetic properties of 5'-nucleotidase from guinea-pig skeletal muscle.

5'-Nucleotidase (EC 3.1.3.5) has been solubilized and purified 1200-fold from guinea-pig skeletal muscle, to a specific activity of 40 U/mg protein. The purified enzyme yields a single protein band on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Guinea-pig skeletal muscle 5'-nucleotidase is extremely sensitive to inhibition by nucleoside di- and triphosphates. The inhibition is of the competitive type, and can be reversed only by strong excess of Mg2+. Nucleoside diphosphates are more powerful inhibitors than nucleoside triphosphates. The Ki values for ADP and ATP are 0.036 and 0.28 microM, respectively. The purified enzyme does not require exogenous cations for maximal activity and is inhibited by EDTA. This inhibition is reversed by divalent cations. This indicates that the enzyme contains a tightly bound metal cation.

5'-Nucleotidase↗
PubMed1985

Effects of dithiothreitol, dithioerythritol and chelating agents on 5'-nucleotidase from bull seminal plasma.

5'-Nucleotidase from bull seminal plasma is inhibited by dithiothreitol and dithioerythritol. These reactives proved to dissociate the dimeric glycoprotein 5'-nucleotidase of Mr 160 000 into two subunits of apparent Mr 80 000, indicating that the subunits are held together by interchain disulfide bridges. HPLC determinations of cysteic acid and carboxymethylcysteine protein derivatives resulted in 50 +/- 3 half-cystine plus cysteine residues, while 1.9 +/- 0.4 free cysteine residues were estimated by HPLC analysis. The enzyme is inhibited by EDTA and EGTA, and the inhibition appears to be of the non-competitive type for both the chelating agents. Experiments for the enzyme activity recovery by MgCl2 and CaCl2 additions, after the EDTA and EGTA treatments in the presence of 8 M urea, are reported.

5'-Nucleotidase↗
PubMed1979

[Enzymologic characterization of adenosine nucleosidase of medicinal plants (Medicago sativa)].

Adenosine nucleosidase (adenosine ribohydrolase, E C 3.2.2.7) was purified from alfalfa leaf juice. The final preparation shows a single band on polyacrylamide gel electrophoresis; the enzyme activity is stable for 12 hrs between pH 5.5 and pH 8.5, but is completely lost on heating at 55 degrees C for 10 min. Optimal pH for the hydrolysis of adenosine is between pH 5 and pH 6. Among nine purine nucleosides tested, only adenosine, 2'-deoxyadenosine and purine riboside were hydrolyzed by the enzyme preparation. A Km value of 7 x 10(-6) M was found with adenosine as substrate at pH 7.4. Of the two reaction products, adenine exerted a weak inhibitory effect, while D-ribose was without effect on the initial rate of adenosine hydrolysis. The data reported are compared with those obtained on the enzymes from other plant sources.

Adenosine↗