PubMed Health⌕ Search

Biomedical subjects

C Stefan

Publications and source records attributed to C Stefan.

At least 19 recordsLinked to original sources
PubMed1999

An ecto-nucleotide pyrophosphatase is one of the main enzymes involved in the extracellular metabolism of ATP in rat C6 glioma.

The presence of a nucleotide pyrophosphatase (EC 3.6.1.9) on the plasma membrane of rat C6 glioma has been demonstrated by analysis of the hydrolysis of ATP labeled in the base and in the alpha- and gamma-phosphates. The enzyme degraded ATP into AMP and PPi and, depending on the ATP concentration, accounted for approximately 50-75% of the extracellular degradation of ATP. The association of the enzyme with the plasma membrane was confirmed by ATP hydrolysis in the presence of a varying concentration of pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a membrane-impermeable inhibitor of the enzyme. PPADS concentration above 20 microM abolished the degradation of ATP into AMP and PPi. The nucleotide pyrophosphatase has an alkaline pH optimum and a Km for ATP of 17 +/- 5 microM. The enzyme has a broad substrate specificity and hydrolyzes nucleoside triphosphates, nucleoside diphosphates, dinucleoside polyphosphates, and nucleoside monophosphate esters but is inhibited by nucleoside monophosphates, adenosine 3',5'-bisphosphate, and PPADS. The substrate specificity characterizes the enzyme as a nucleotide pyrophosphatase/phosphodiesterase I (PD-I). Immunoblotting and autoadenylylation identified the enzyme as a plasma cell differentiation antigen-related protein. Hydrolysis of ATP terminates the autophosphorylation of a nucleoside diphosphate kinase (NDPK/nm23) detected in the conditioned medium of C6 cultures. A function of the pyrophosphatase/PD-I and NDPK in the purinergic and pyrimidinergic signal transduction in C6 is discussed.

Adenosine Triphosphate↗
PubMed1998

Growth-related expression of the ectonucleotide pyrophosphatase PC-1 in rat liver.

Plasma cell differentiation antigen-1 (PC-1) is a 5'-ectonucleotide pyrophosphatase that has been implicated in various processes including insulin- and nucleotide-mediated signaling and cell growth. We show here that the expression of both PC-1 mRNA and protein in rat liver and in hepatoma cells is strictly growth-related. Thus, the level of PC-1 in FAO hepatoma cells increased with the cell density. PC-1 was not expressed in the neonatal rat liver, but gradually appeared in the first weeks of age, to reach adult levels around the weaning period. Furthermore, PC-1 protein and mRNA largely disappeared from the liver within 24 hours following a hepatectomy of 70%, but re-appeared in the later phases (3-15 days) of the ensuing regeneration period. An equally rapid loss of PC-1 protein and mRNA could also be provoked in normal livers by the administration of the translational inhibitor, cycloheximide, but the transcriptional inhibitors, actinomycin D and alpha-amanitin, did not show these effects. Nuclear run-on assays revealed that the loss of PC-1 mRNA after hepatectomy or after the administration of cycloheximide was not caused by a decreased transcription of the PC-1 gene, suggesting that the level of PC-1 is controlled by an mRNA-stabilizing protein that is lost after hepatectomy and has a high turnover.

Aging↗
PubMed1998

[Cataract and the exfoliative syndrome].

Exfoliation syndrome is more frequently in the older age and represents a risk factor for cataract surgery. This paper presents the results of a clinical trial made on 436 patients with troubles of transparency of the lens who were investigate in our clinic during January 1995-January 1997, and in whom, clinic and paraclinic exams have not revealed any associated ocular disease. In 14% of these patients who presented troubles of transparency of the lens were found uni- or bilateral exfoliation. The authors present the treatment applied both in patients in clinical follow-up (50% of patients with exfoliation syndrome develop secondary glaucoma) and patients who underwent surgical treatment. The patients with exfoliation syndrome and cataract have had a high risk to develop intra- and postoperative complications. The surgical treatment suggested by authors is extracapsular cataract extraction, either or without lens implantation and peripheral iridectomy which represents a compulsory step.

Aged↗
PubMed1997

[Pseudotumoral tuberculous choroiditis].

It is presented a case of a secondary tumoral retinal detachment that clinical examination and all paraclinical investigation go for a choroidal malignant melanoma. The anatomopathological examination of the enucleated eyeball has surprisingly put in evidence some choroidal consumptive lesions.

Adult↗
PubMed1996

Threonine autophosphorylation and nucleotidylation of the hepatic membrane protein PC-1.

The membrane protein plasma-cell-differentiation antigen 1 (PC-1) has been described as a phosphodiesterase-I/nucleotide pyrophosphatase and as an autophosphorylating protein kinase. It has been suggested, however, that PC-1 is not a real protein kinase and that the autophosphorylated enzyme represents a nucleotidylated derivative, which is formed on Thr238 (murine PC-1) as a catalytic intermediate during ATP hydrolysis [Belli, S.I., Mercuri, F.A., Sali, A.& Goding, J.W. (1995) Eur. J. Biochem. 228, 669-676]. We have investigated the proposed multifunctional role of PC-1 and show here that ATP hydrolysis and autophosphorylation represent two distinct catalytic reactions. The enzyme was radiolabeled when various concentrations (1-260 microM) of [alpha-32P]ATP or [alpha-32P]ADP, but not [gamma-32P]ATP, were used as substrates for the formation of the pyrophosphatase catalytic intermediate, especially in the presence of imidazole, which interferes with the hydrolysis of the nucleotidylated enzyme. In contrast, autoradiography revealed autophosphorylation only with [gamma-32P]ATP as the phosphoryl donor, and autophosphorylation has been shown to occur only at ATP concentrations below 5 microM. Autophosphorylation could also be differentiated from nucleotidylation by its higher resistance to alkaline treatment and its more basic pH optimum. An intestinal nucleotide pyrophosphatase with a structurally related catalytic site could not be autophosphorylated, which shows that autophosphorylation is not an intrinsic property of the nucleotide pyrophosphatase reaction. Autophosphorylation of PC-1 was associated with inactivation of its phosphodiesterase-I/nucleotide-pyrophosphatase activity. We propose that autophosphorylation of PC-1 on Thr238 at low ATP concentrations serves as an autoregulatory mechanism that makes Thr238 unavailable for participation in the hydrolysis of extracellular nucleotides when they become scarce.

Adenine Nucleotides↗
PubMed1996

The inhibition of the insulin receptor by the receptor protein PC-1 is not specific and results from the hydrolysis of ATP.

The membrane protein plasma cell differentiation antigen 1 (PC-1) has been purified as an inhibitor of insulin receptor tyrosine kinase activity and has been implicated in the pathogenesis of NIDDM. However, we show here that PC-1 is a general protein kinase inhibitor in vitro and that this inhibition results from the hydrolysis of ATP by the intrinsic nucleotide pyrophosphatase activity of PC-1. Thus, the inhibition diminished with increasing ATP concentrations, and it was nullified when the ATP concentration was kept constant with a regenerating system or when ATP was added repetitively. When care was taken to avoid ATP depletion, PC-1 did not affect the insulin sensitivity of insulin receptor autophosphorylation. We conclude that the reported inhibition of insulin signaling by PC-1 does not result from a direct inhibition of the insulin receptor kinase activity.

Adenosine Triphosphate↗
PubMed1995

Signalling mechanisms and oxidative stress in apoptosis.

A variety of stimuli can induce cells to undergo apoptotic death. One of the most reproducible inducers is mild oxidative stress, be it via exposure to hydrogen peroxide, redox-cycling quinones or thiol-alkylating agents. Oxidative modifications of proteins and lipids have also been observed in cells undergoing apoptosis in response to non-oxidative stimuli such as glucocorticoids or topoisomerase II inhibitors. This suggests that some unidentified oxidative changes occur during apoptosis in many, if not all, cases. However, recent experiments demonstrating apparently normal apoptosis even when cells are cultured at low oxygen tensions show that reactive oxygen species cannot be essential mediators of this type of cell death. Experiments revealing that apoptosis is typically accompanied by a depletion of intracellular reduced glutathione (GSH) are also discussed. As GSH depletion will lower a cell's capacity to buffer against endogenous oxidants, we propose that it contributes to the increased oxidative damage commonly observed to accompany apoptosis. In addition, it may set a time limit on continued mitochondrial function (and thus indirectly on total ATP levels and membrane integrity) in apoptotic cells, and thereby explain the often observed 'secondary necrosis' of cells undergoing apoptosis in vitro.

Animals↗
PubMed1991

Molecular cloning and characterization of the gene encoding the adenine methyltransferase M.CviRI from Chlorella virus XZ-6E.

The gene encoding the DNA methyltransferase M.CviRI from Chlorella virus XZ-6E was cloned and expressed in Escherichia coli. M.CviRI methylates adenine in TGCA sequences. DNA containing the M.CviRI gene was sequenced and a single open reading frame of 1137 bp was identified which could code for a polypeptide of 379 amino acids with a predicted molecular weight of 42,814. Comparison of the M.CviRI predicted amino acid sequence with another Chlorella virus and 14 bacterial adenine methyltransferases revealed extensive similarity to the other Chlorella virus enzyme.

Amino Acid Sequence↗
PubMed1991

A comparative study on involvement of tPA activity in ovulation induced by hCG and GnRH agonist in hypophysectomized rats.

A GnRH agonist (5-50 micrograms) is capable of inducing ovulation in PMSG-primed hypophysectomized immature rats, as is the case in hCG-induced ovulation, but 2-4 h earlier than hCG. GnRH-induced ovulation is effectively blocked by the concomitant administration of the GnRH-antagonist which failed to interfere with hCG-induced ovulation, indicating that GnRH and its agonists do not share a receptor with LH/hCG. Like hCG, GnRH is also capable of inducing tissue type (tPA), but not urokinase type (uPA) PA. The plasminogen activator activity in ovarian homogenates and the granulosa and theca-interstitial cells increase in a time-dependent manner, reaching maximum levels just prior to ovulation. Similar to hCG, GnRH also increases tPA activity in cumulus-oocyte complexes in a time-dependent fashion.

Animals↗
PubMed1982

[Lipid electrophoresis in the alcoholic. Features and usefulness in the diagnosis of various degrees of alcoholic liver diseases].

Reference is made to the importance of assessing serum lipoproteins by conventional agarose gel electrophoresis in the preliminary diagnosis of the degree of severity of a liver disease. A comparison is made between lipidogram changes in 48 alcoholic patients with the liver histologies following needle biopsy according to Menghini. The conclusion is drawn that in acute and chronic alcoholic liver disease there is a characteristic lipidogram profile, marked by a double "camel's hump" in the bands due to predominance of the beta and prebeta-lipoprotein fractions. This, in turn, is related to the liver steatosis observed bioptically. In macro and micronodular cirrhosis, however, examination of the electrophoretic lipid fractions is frequently unhelpful. Attention is drawn to the appearance of the alpha fraction as a presumably pointer to the condition in question. It is felt that this conventional, simple evaluation of lipoproteins is a valuable diagnostic test in assessing the seriousness of alcoholic liver disease.

Adult↗
PubMed1982

An investigation of the construct validity of the Bannister-Fransella Grid Test of Schizophrenic Thought Disorder.

An attempt was made to demonstrate the construct validity of the Grid Test in a psychiatric population by showing that: (a) judgements of thought disorder based on the Grid Test were associated with judgements based on a clinical interview; (b) Grid Test scores were not associated with measures of other forms of psychopathology, intelligence, or memory. Results of a principal components factor analysis confirmed both hypothesis, supporting the validity of the Grid Test as a measure of thought disorder.

Diagnosis, Differential↗
PubMedDate not supplied

Homeostasis changes induced by the action of ethanol on the materno-fetal complex in rats. VII. Effects on some alkaline and alkaline-earth metals of blood serum.

The effect of chronic biparental preconceptional alcoholization followed by alcohol consumption during the preimplantation period on the maternal and fetal homeostasis of some alkaline and alkaline-earth metals was studied in albino rats. Female and male rats consumed 20% ethanol (v/v) for 50-60 days before mating (group E). Further on pregnant females were alcoholized until day 5 of pregnancy. Control females and males consumed tap water (group C). Animals were sacrificed on day 20 of pregnancy. Blood samples were obtained from fetuses (the blood of each litter being pooled) and from pregnant females. Biochemical determinations were made by atomic emission spectroscopy for Na and K and by atomic absorption spectroscopy for Ca and Mg. Early and late mortality of conceptuses were checked. Non significant changes were observed within group E in the maternal serum as to Na (increase) and K(decrease), while Ca and Mg showed a significant decrease. Similar changes were found in the pooled fetal serum, the decrease of K and Mg being less marked. No structural anomalies were detected. With respect to tanatogenesis, both early resorptions and late fetal death were increased.

Animals↗