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E Villar

Publications and source records attributed to E Villar.

At least 73 records · Page 4Linked to original sources
PubMed1991

Activity of influenza C virus O-acetylesterase with O-acetyl-containing compounds.

Influenza C virus (strain C/Johannesburg/1/66) was grown, harvested, purified and used as source for the enzyme O-acetylesterase (N-acyl-O-acetylneuraminate O-acetylhydrolase; EC 3.1.1.53). This activity was studied and characterized with regard to some new substrates. The pH optimum of the enzyme is around 7.6, its stability at different pH values shows a result similar to that of the pH optimum, and its activity is well maintained in the pH range from 7.0 to 8.5 (all these tests were performed with 4-nitrophenyl acetate as substrate). Remarkable differences were found in the values of both Km and Vmax, with the synthetic substrates 4-nitrophenyl acetate, 2-nitrophenyl acetate, 4-methylumbelliferyl acetate, 1-naphthyl acetate and fluorescein diacetate. The use of 4-nitrophenyl acetate, 4-methylumbelliferyl acetate or 1-naphthyl acetate as substrate seems to be convenient for routine work, but it is better to carry out the measurements in parallel with those on bovine submandibular gland mucin (the latter is a natural and commercially available substrate). It was found that 4-acetoxybenzoic acid, as well as the methyl ester of 2-acetoxybenzoic acid, but not 2-acetoxybenzoic acid itself, are cleaved by this enzyme. Triacetin, di-O-acetyladenosine, tri-O-acetyladenosine, and di-O-acetyl-N-acetyladenosine phosphate, hitherto unreported as substrates for this viral esterase, are hydrolysed at different rates by this enzyme. We conclude that the O-acetylesterase from influenza C virus has a broad specificity towards both synthetic and natural non-sialic acid-containing substrates. Zn2+, Mn2+ and Pb2+ (as their chloride salts), N-acetylneuraminic acid, 4-methyl-umbelliferone and 2-acetoxybenzoic acid (acetylsalicylic acid) did not act as inhibitors.

Acetylesterase↗
PubMed1991

On the inhibition mechanism of the sialidase activity from Newcastle disease virus.

N-Acetylneuraminic, 2-deoxy-2,3-didehydro-N-acetylneuraminic acid and the beta anomer of methoxyneuraminic acid (Neu5Ac, Neu5Ac2en, MeONeu) have been used as probes for the catalytic mechanism of the activities of the outer membrane-bound haemagglutinin-neuraminidase (HN) from newcastle disease virus (NDV). Neu5Ac and Neu5Ac2en produced a competitive inhibition of the sialidase (= neuraminidase) activity, whereas MeONeu had no effect on this activity. This lack of inhibition can be explained by the free amino-acid group lacking the acetyl substituent in the MeONeu. Neu5Ac2en produced the highest inhibition. Based on the effect of the inhibitors, a reaction mechanism is suggested. On the other hand, the above mentioned inhibitors of the sialidase activity had no effect on haemagglutinating activity, suggesting different active sites for the both activities.

HN Protein↗
PubMed1990

Sialidase activity in rimantadine-resistant and -sensitive influenza A viruses.

Rimantadine-resistant and -sensitive influenza A variants were assayed for their sialidase (neuraminidase, EC 3.2.1.18) activity. The kinetic parameters determined (pH optimum, stability against different pH values, thermal stability, activity on methylumbelliferyl-alpha-D-N-acetylneuraminic acid, N-acetylneuraminyl-lactose, fetuin and bovine submandibular gland mucin as substrates, Km with the former substrate, inhibition by two competitive inhibitors, and behavior towards amantadine) revealed the same results for both variants of the virus. Thus, it can be deduced that resistance to rimantadine does not influence the sialidase activity of influenza A virus.

Animals↗
PubMed1989

Proteins of Newcastle disease virus envelope: interaction between the outer hemagglutinin-neuraminidase glycoprotein and the inner non-glycosylated matrix protein.

Using linear sucrose-density ultracentrifugation analysis of Triton-solubilized Newcastle Disease Virus envelopes, we have evidenced, for the first time, the existence of interactions between the outer hemagglutinin-neuraminidase transmembrane glycoprotein and the inner non-glycosylated peripheral matrix protein. Such interactions seem to be electrostatic. These conclusions are based on the behavior of both proteins at different ionic strengths. When in low ionic strength buffer, hemagglutinin-neuraminidase and matrix proteins band together in the sucrose gradient, whereas at high ionic strength both proteins band at different rates in the gradient. The behavior of the inner matrix protein in our conditions was the expected one for a peripheral protein. The results of these 'in vitro' studies are also discussed in terms of the possible 'in vivo' role of such interactions.

Animals↗
PubMed1989

Kinetic studies on the sialidase of three influenza B and three influenza A virus strains.

Sialidase of influenza virus type A has been extensively studied through structural and kinetic approaches. However, sialidase of influenza virus type B has been less investigated. In this work, we have studied the activity and some properties (optimal pH, KM, Vmax, thermal stability) of sialidase in three influenza virus strains of type B (circulating in the period 1983-86) and also the activity and properties of sialidase from three virus strains of type A circulating at the same period of time. The results show that the activity and the Vmax was always higher for sialidase of type A viruses relative to those values of type B. Differences were also found for optimal pH and, in some cases, for thermal stability of the sialidase between strains belonging to the influenza viruses type A and B. However, the behaviour for the sialidase in all strains was very similar towards two competitive inhibitors. Thus, it could be suggested that the evolution pattern of the sialidase of both types of influenza viruses determines some modifications which result in a higher efficiency for sialidase of some strains of influenza virus type A, but maintaining in the two types of viruses a similar behaviour towards competitive inhibitors.

Animals↗
PubMed1985

C1-Tetrahydrofolate synthase from rabbit liver. Structural and kinetic properties of the enzyme and its two domains.

C1-Tetrahydrofolate synthase is a multifunctional enzyme which catalyzes three reactions in 1-carbon metabolism: 10-formyltetrahydrofolate synthetase; 5,10-methenyltetrahydrofolate cyclohydrolase; 5,10-methylenetetrahydrofolate dehydrogenase. A rapid 1-day purification procedure has been developed which gives 40 mg of pure enzyme from 10 rabbit livers. The 10-formyltetrahydrofolate synthetase activity of this trifunctional enzyme has a specific activity that is 4-fold higher than the enzyme previously purified from rabbit liver. Conditions have been developed for the rapid isolation of a tryptic fragment of the enzyme which contains the methylenetetrahydrofolate dehydrogenase and methenyltetrahydrofolate cyclohydrolase activities. This fragment is a monomer exhibiting a subunit and native molecular weight of 36,000 in most buffers. However, in phosphate buffers the native molecular weight suggests that the fragment is a dimer. Conditions are also given whereby chymotryptic digestion allows the simultaneous isolation from the native enzyme of a large fragment containing the 10-formyltetrahydrofolate synthetase activity and a smaller fragment containing the dehydrogenase and cyclohydrolase activities. The large fragment is a dimer with a subunit molecular weight of 66,000. The small fragment retains all of the dehydrogenase and cyclohydrolase activities of the native enzyme. The large fragment is unstable but retains most of the 10-formyltetrahydrofolate synthetase activity. Km values of substrates for the two fragments are the same as the values for the native enzyme. The 10-formyltetrahydrofolate synthetase activity of the native enzyme requires ammonium or potassium ions for expression of full catalytic activity. The effect of these two ions on the catalytic activity of the large chymotryptic fragment is the same as with the native enzyme. We have shown by differential scanning calorimetry that the native enzyme contains two protein domains which show thermal transitions at 47 and 60 degrees C. Evidence is presented that the two domains are related to the two protein fragments generated by proteolysis of the native enzyme. The larger of the two domains contains the active site for the 10-formyltetrahydrofolate synthetase activity while the smaller domain contains the active site which catalyzes the dehydrogenase and cyclohydrolase reactions. Replacement of sodium ion buffers with either ammonium or potassium ions results in an increase in stability of the large domain of the native enzyme. This change in stability is not accompanied by a change in the quaternary structure of the enzyme.(ABSTRACT TRUNCATED AT 400 WORDS)

Aminohydrolases↗
PubMed1985

Serine hydroxymethyltransferase from Escherichia coli: purification and properties.

Serine hydroxymethyltransferase from Escherichia coli was purified to homogeneity. The enzyme was a homodimer of identical subunits with a molecular weight of 95,000. The amino acid sequence of the amino and carboxy-terminal ends and the amino acid composition of cysteine-containing tryptic peptides were in agreement with the primary structure proposed for this enzyme from the structure of the glyA gene (M. Plamann, L. Stauffer, M. Urbanowski, and G. Stauffer, Nucleic Acids Res. 11:2065-2074, 1983). The enzyme contained no disulfide bonds but had one sulfhydryl group on the surface of the protein. Several sulfhydryl reagents reacted with this exposed group and inactivated the enzyme. Spectra of the enzyme in the presence of substrates and substrate analogs showed that the enzyme formed the same complexes and in similar relative concentrations as previously observed with the cytosolic and mitochondrial rabbit liver isoenzymes. Kinetic studies with substrates showed that the affinity and synergistic binding of the amino acid and folate substrates were similar to those obtained with the rabbit liver isoenzymes. The enzyme catalyzed the cleavage of threonine, allothreonine, and 3-phenylserine to glycine and the corresponding aldehyde in the absence of tetrahydrofolate. The enzyme was also inactivated by D-alanine caused by the transamination of the active site pyridoxal phosphate to pyridoxamine phosphate. This substrate specificity was also observed with the rabbit liver isoenzymes. We conclude that the reaction mechanism and the active site structure of E. coli serine hydroxymethyltransferase are very similar to the mechanism and structure of the rabbit liver isoenzymes.

Amino Acid Sequence↗
PubMed1984

Purification, characterization and kinetics of beta-N-acetylhexosaminidases A and B from the slug Arion rufus L.

Two beta-N-acetylhexosaminidases have been purified to homogeneity and characterized, from the digestive gland of the slug A. rufus L., showing very high specific activities. Hexosaminidase A (Hex A) was purified 1300-fold with a yield of 12%, and hexosaminidase B (Hex B) was purified 1400-fold with a yield of 20%. Purified Hex A or Hex B run as a single protein band in polyacrylamide gel disc electrophoresis, showing different mobilities. The purified preparations do not show any of the other glycosidase activities present in the crude extract. beta-N-acetylglucosaminidase (GlcNAc-ase) and beta-N-acetylgalactosaminidase (GalNAc-ase) activities are always associated in a single peak for each enzyme form, with constant activity ratio, in all the purification steps, since they are catalyzed by the same enzyme (Hex A or Hex B). The optimal pH for both forms are 4.5 for GlcNAc-ase and 4.0 for GalNAc-ase activity. Hex B shows thermal and pH-stability higher than Hex A. The isoelectric points are 4.5 and 5.5 for A and B forms, respectively. The molecular weight is 150 000 for Hex A and 320 000 for Hex B. The amino acid composition of purified Hex A and B presents some differences concerning particularly Cys, Thr, Ser, Glu and Ile. The ratios Vmax/Km show that GlcNAc-ase is the main activity of both enzyme forms. beta-N-acetylglucosides and beta-N-acetylgalactosides completely compete for a common active site in mixed-substrates experiments. The Ki values are always coincident for GlcNAc-ase and GalNAc-ase activities, using competitive inhibitors (the corresponding lactones). These results strongly suggest that both activities are catalyzed by the same active site in both Hex A and B. Inhibition of the enzyme activities was found with the corresponding lactones, N-acetyl hexosamines, mannose, mannosides, HgCl2 and lead acetate; activation, with ribose, and with some chlorides and sulphates of divalent cations.

Acetylglucosaminidase↗
PubMed1982

[Glycosidases of various mollusks: general properties, kinetic studies and action on natural substrates].

The beta-N-acetylhexosaminidase, beta-glucuronidase, alpha-galactosidase, beta-galactosidase and alpha-L-fucosidase activities, in six different species of molluscs, have been studied. The optimum pH was acid in all cases, in agreement with the lysosomal origin of these enzymes. They generally show several pI in their isoelectrofocusing profiles. Kinetic studies with enzymes having several activities in one protein, i.e. beta-N-acetylhexosaminidase and beta-galactosidase, have been carried out with mixed substrates in order to determine the occurrence of several active sites. The action of these enzymes on glycosidic rests containing natural substrates has been studied by enzymatic hydrolysis.

Animals↗
PubMed1978

Comparative studies on blood serum alpha-L-fucosidases from several mammalian species.

1. Peripheral blood serum alpha-L-fucosidases have been studied from various mammalian species: Sus scropha var domestica L. (pig), Capra hircus L. (goat), Bos taurus L. (bull, races Morucha and Charolais), Equus caballus L. (horse) and Equus asinus L. (donkey). 2. Fluorimetric and spectrophotometric procedures were used for determination of alpha-L-fucosidases. 3. alpha-L-Fucosidases were more active towards fluorescent substrates than towards chromogenic substrates. 4. pH optima values of the enzymes are: (A) 5.5 for sera from all above-mentioned species when fluorescent substrates were employed; (B) 4.0 for goat, 4.5 for bull, 5.0 for pig and 4.5-5.0 for horse and donkey sera when chromogenic substrates were used. 5. pH activity profiles are very similar for two races (Morucha and Charolais) of the same species (Bos taurus L.) and also for two species of the same genus (Equus caballus and Equus asinus L.). 6. These serum alpha-L-fucosidases are very labile under heat treatment, even at 37 degrees C.

Animals↗
PubMedDate not supplied

Non-typhi Salmonella bacteraemia.

We reviewed retrospectively the clinical records of patients with non-typhi Salmonella bacteraemia in our hospital from 1979 to 1988. During the study period 45 non-typhi Salmonella bacteraemias were diagnosed in 43 patients. Ten patients were under one year old and 11 were over 60. Seven cases of sepsis presented in patients with AIDS. Only three episodes were nosocomially acquired. In two of three patients the bacteraemia was preceded by an episode of acute gastroenteritis and one third presented without gastroenteritis. Complications and mortality were infrequent in spite of the differing degrees of adequacy of antibiotic treatment which was inappropriate in many cases. We have attempted to assess optimal antibiotic therapy, taking into account the duration and means of administration, in different groups of patients with nontyphi Salmonella bacteraemia.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Prospective study of the enzymatic activities in urine of N-acetyl-beta-D-glucosaminidase, alpha-D-mannosidase, alpha- and beta-D-glucosidases, alpha-L- and beta-D-fucosidases, and beta-D-galactosidase in type I diabetes mellitus with early nephropathy.

Different surveys have been carried out on the plasma activities of different glycosidases in patients with insulin-dependent diabetes mellitus, but research on urinary glycosidases in this disease is scanty and incomplete. To elucidate the behavior of these lysosomal enzymes in the metabolic alterations occurring in the glomerular basal membrane during the initial stages of diabetic nephropathy, we conducted a prospective study to examine the urinary activities of N-acetyl-beta-D-glucosaminidase (NAG), alpha-D-mannosidase, alpha- and beta-D-glucosidase, alpha-L- and beta-D-fucosidase, and beta-D-galactosidase in patients with type I insulin-dependent diabetes mellitus, surveyed over 18 months, whose early diabetic nephropathy was detected by the presence of microalbuminuria. The simultaneous determination of beta 2-microglobulin in urine confirmed the glomerular origin of the albuminuria. No statistically significant correlation was found between the levels of albuminuria and the activities of any of the glycosidases analyzed. In the diabetic patients, a significant decrease was observed in the activities of all the enzymes (p < 0.05), except NAG and alpha-D-mannosidase, although the decrease in the latter was very close to statistical significance (p = 0.028, unilateral; p = 0.057 bilateral). Similarly, in the patients, there was a significant negative correlation (p < 0.05) with the serum levels of fructosamine, except with beta-D-galactosidase, which showed a positive correlation (p < 0.05) with fructosamine and blood HbA1c.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylglucosaminidase↗
PubMedDate not supplied

Comparison of biological and physical properties of human and animal A(H1N1) influenza viruses.

The study of biological properties of influenza virus strains belonging to the same subtype A(H1N1) and closely antigenically related, but isolated from different animal species (man, pig and duck), demonstrated that avian strains were more resistant than those isolated from mammals to high temperature and low pH, as shown by titration of residual infectivity in cell cultures (MDCK) and by sialidase assay. The difference in behaviour could be correlated to biological adaptation of the virus to its host. Avian body temperature is 40 degrees C and influenza virus, in ducks, is enterotropic and therefore capable of passing through the low pH values in the upper digestive tract of the animal. These results do not contradict the hypothesis of a possible filiation between avian and mammalian orthomyxoviruses.

Animals↗
PubMedDate not supplied

bcl-2 Expression and apoptosis in primary and metastatic breast carcinomas.

OBJECTIVES: To evaluate the role of bcl-2 and apoptotic index in the progression from primary to metastatic breast carcinoma and their influence on prognosis. METHODS: bcl-2 expression was examined by immunohistochemistry and apoptotic index by in situ end-labelling in 116 surgical breast carcinomas and lymph node metastases from 50 patients. RESULTS: bcl-2 was observed in 69 cases (59.4%) of primitive carcinomas and 26 cases (65%) of metastatic breast carcinomas and there was agreement of bcl-2 expression between primary and metastatic sites except in 3 cases. bcl-2 expression was significantly associated with several favourable prognostic features, such as small tumour size (p = 0.03) and oestrogen and progesterone-receptor positivity (p < 0.01 and p < 0.001, respectively). A high apoptotic index was significantly associated with a number of poor prognostic factors, including poorly differentiated carcinomas, large tumour size, high Ki67 expression and high mitotic count (p < 0.001 in all cases). The mean apoptotic index was higher in lymph node metastasis than in primary carcinomas (1.19 vs. 0.69, p < 0.01). A low bcl-2 expression and a high apoptotic index were significantly associated with short-relapse free survival rates (p = 0.02 and p < 0.01, respectively), but only apoptotic extent provided independent prognostic information by multivariate analysis. CONCLUSIONS: The evaluation of bcl-2 expression and extent of apoptosis may provide useful prognostic information on breast cancer patients; however while increased apoptosis is strongly associated with the progression from primary carcinomas to lymph node metastases, bcl-2 does not seem to play a significant role in this process.

Adult↗
PubMedDate not supplied

Expression of bax and p53 proteins in the tumorigenesis and progression of breast carcinomas.

OBJECTIVES: Dysregulation of normal programmed cell death mechanisms plays an important role in the pathogenesis of breast cancer. The purpose of this study was to investigate the role of bax and p53 expression in tumorigenesis and progression of breast carcinoma as well as their relationship with proliferative and apoptotic activity. METHODS: We used immunohistochemical methods and in situ detection of apoptotic cells to examine 30 carcinomas in situ (CIS), 131 invasive breast carcinomas and 45 lymph node metastases. RESULTS: In 25% (33 of 131) of invasive breast carcinomas examined, bax expression was absent, while p53 accumulation was present in 37% (49 of 131). Interestingly, p53 accumulation and loss of bax expression occur in breast CIS as frequently as in invasive breast carcinoma. Thus, in 17% (5 of 30) of CIS bax expression was absent, and 30% (9 of 30) presented nuclear expression of p53. p53 accumulation was related to apoptosis and proliferative activity. However, the protein level of bax was unrelated to all parameters studied, including proliferation and apoptosis of tumor cells. A multivariate analysis of disease-free survival demonstrated that p53 accumulation and bax expression are not significant independent indicators of prognosis in operable breast carcinoma. Our results also show that the proportion of bax- and p53-positive cells does not vary between primary and metastatic tumors. CONCLUSIONS: p53 accumulation and loss of bax expression influence the acquisition of a malignant phenotype but seem to have no further impact on tumor progression.

Adult↗