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Biomedical subjects

M Losada

Publications and source records attributed to M Losada.

At least 37 records · Page 2Linked to original sources
PubMed1993

ATP-driven transhydrogenation and ionization of water in a reconstituted glyceraldehyde-3-phosphate dehydrogenases (phosphorylating and non-phosphorylating) model system.

In an unbuffered medium, an intense acidification occurs during the oxidation of D-glyceraldehyde-3-phosphate (G3P) to 3-phospho-D-glycerate (PGA) catalyzed by NADP(+)-specific non-phosphorylating G3P dehydrogenase, an enzyme that photosynthetic eukaryotic cells contain exclusively in their cytosol. The true enzymatic character of this proton release is the consequence of the following redox/acid-base reaction: G3P + NADP+ + H2O-->PGA + NADPH + 2H+. When the well-established ATP-dependent reduction of PGA to G3P, catalyzed by PGA kinase and NAD(+)-specific phosphorylating G3P dehydrogenase, was coupled through the intermediate G3P to the above reverse oxidation reaction, a transient alkalinization of the medium followed by its acidification accompanied transhydrogenation from NADH to NADP+. The significance of the observed endergonic transhydrogenation and ionization of water at the expense of the chemical energy of ATP in this reconstituted enzyme system as well as its relevance for the export of reducing power (H-) across the chloroplast membrane and the maintenance of the pH gradient that exists between the stroma and the cytosol are discussed.

Adenosine Triphosphate↗
PubMed1993

Subclavian catheter-related infection is a major risk factor for the late development of subclavian vein stenosis.

Although subclavian vein stenosis is a well-known complication of haemodialysis subclavian catheters, little is known about its causes. Catheter-related infection is the most common complication of this technique, but its role in the genesis of late subclavian stenosis has not been established. We retrospectively analysed 80 subclavian catheterizations in a total of 54 chronic haemodialysis patients from a single center. Sixteen catheters had to be removed because of a well documented catheter-related infection: three catheter-related sepsis (2 with ipsilateral phlebitis), seven isolated fever with catheter tip colonization which disappeared after catheter removal, and six exit-site discharge with positive culture. For comparison we matched 14 contemporaneous catheters which were electively removed without evidence of infection and with a negative culture of the catheter tip. A venogram of the ipsilateral arm was performed in all the cases after more than 6 months of catheter removal. Both groups were remarkably similar with respect to age, sex, side of insertion, number of inserted catheters, time of indwelling, and time elapsed from removal to venography. Definite subclavian stenosis was three times more common among patients with previous catheter-related infection (75% versus 28%; P < 0.01). Interestingly, both patients with ipsilateral phlebitis showed total occlusion of the subclavian vein. Although all diabetic patients of the study (n = 6) suffered a catheter-related infection, the incidence of late subclavian stenosis was not more common than in non-diabetic infected patients. In summary, subclavian haemodialysis catheter-related infection is a major risk factor for the development of late subclavian vein stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Differential regulation by trophic conditions of phosphorylating and non-phosphorylating NADP(+)-dependent glyceraldehyde-3-phosphate dehydrogenases in Chlorella fusca.

The two NADP(+)-dependent glyceraldehyde-3-phosphate dehydrogenases present in the green alga Chlorella fusca, namely, the phosphorylating (chloroplastic) enzyme and the non-phosphorylating (cytosolic) enzyme, are differently affected by the trophic conditions prevailing in the cell cultures. The addition of metabolizable sugars to cell cultures growing in the light promotes a marked decrease of the phosphorylating enzyme activity down to a barely detectable cellular level. In contrast, the cellular level of the non-phosphorylating enzyme is even enhanced in the presence of such sugars. These effects are not observed, however, with a number of non-assimilable sugar analogs. After sugar removal, a recovery of the phosphorylating activity--in a process which is inhibited by cycloheximide but not by lincomycin--is observed in illuminated cells but not in darkness, thus indicating a light-dependent nuclear synthesis of the chloroplastic enzyme. It seems therefore that the two dehydrogenases are adaptative enzymes subject to differential regulation by nutritional conditions.

Carbohydrates↗
PubMed1991

Decentration of intraocular lenses implanted after intercapsular cataract extraction (envelope technique).

Pseudophakos decentration produces symptoms such as glare, halos, and other visual aberrations. We have reviewed 161 eyes of patients who had an intercapsular cataract extraction with intraocular lens (IOL) implantation with a follow-up of at least six months. Mean decentration was 0.54 mm. It was 0.46 mm for the lenses implanted symmetrically in the bag, 0.65 mm for those implanted in the sulcus, and 0.91 mm for those implanted asymmetrically (bag-sulcus). The differences between the lenses fixated in the bag and those asymmetrically situated were statistically significant (P less than .001). Circular looped lenses (360-degree encircling loop) decentered less (mean 0.28 mm) than modified C-loop lenses (mean decentration 0.63 mm) and modified J-loop lenses (mean decentration 0.60 mm). These differences were statistically significant (P less than .001). The differences were also significant if we considered only the lenses implanted in the bag (mean decentration 0.20 versus 0.59 and 0.54, respectively) (P less than .0001).

Aged↗
PubMed1991

Etoposide and mitomycin in the treatment of non-small-cell lung cancer. A phase I-II evaluation.

Sixty-five patients (20 patients who had had prior radiotherapy and 45 patients who had not had prior radiotherapy) were entered into a study evaluating escalating doses of etoposide and mitomycin in the treatment of non-small-cell lung cancer (NSCLC). Twenty-two percent of patients who had not received prior radiotherapy responded to the chemotherapy, compared with 5% of patients who had received prior radiotherapy. The best response rate and median survival time was 30% and 31.9 weeks, respectively, seen in three of 10 patients receiving mitomycin 10 mg/M2 i.v. day 1 and etoposide 100 mg/M2 i.v. days 1-3. The major toxicity was hematologic--mainly leukopenia, in 59% of patients who had had no prior radiation therapy and were receiving mitomycin 10 mg/M2 i.v. day 1 and etoposide 150 mg/M2 i.v. days 1-3 (grade 3 and 4 hematologic toxicity). The mitomycin-etoposide drug combination has some activity in patients with NSCLC who have not received prior radiotherapy. The recommended starting dose is mitomycin 10 mg/M2 i.v. day 1 and etoposide 100 mg/M2 i.v. days 1-3, administered every 4 weeks.

Adenocarcinoma↗
PubMed1991

Intrapleural therapy for malignant pleural effusions. A randomized comparison of bleomycin and tetracycline.

Between December 1985 and August 1988, there were 115 patients at 13 centers who were entered on a randomized comparison of tetracycline and bleomycin for treatment of malignant pleural effusions. Fifteen patients were not treated, primarily due to rapid progression of systemic cancer. Fifteen patients entered on a high-dose regimen of bleomycin (120 units) were excluded from this analysis (following early closure of that arm), leaving 85 patients randomized to low-dose bleomycin (60 units; 44 patients) or tetracycline (1 g; 41 patients). Patients were required to have a cytologically positive pleural effusion, good performance status (0, 1, or 2), lung reexpansion following tube thoracostomy with drainage rates of 100 ml/24 or less, no prior intrapleural therapy, no prior systemic bleomycin therapy, no chest irradiation, and no recent (four weeks) change in systemic therapy. A total of 11 patients (five with bleomycin and six with tetracycline) were not evaluable due to technical problems with tube drainage (one), loss to follow-up (two), sudden death due to pulmonary embolus (one), and rapid progression of systemic disease (seven). There were no clinically significant differences in demographic factors, primary site, performance status, or presence of metastases other than pleural effusion. Overall survival did not differ between the two groups. Median time to recurrence or progression of the effusion was 32 days for tetracycline-treated patients and at least 46 days for bleomycin-treated patients (p = 0.037). The recurrence rate within 30 days of instillation was 36 percent (10/28) with bleomycin and 67 percent (18/27) with tetracycline (p = 0.023) (not all patients were restudied in the first 30 days). By 90 days the corresponding recurrence rates were 30 percent (11/37) for bleomycin and 53 percent (19/36) for tetracycline (p = 0.047). Toxicity was similar between groups.

Adult↗
PubMed1990

Monoclonal analysis of fine-needle aspiration biopsy in kidney allografts.

To evaluate changes in T-lymphocyte subsets and DR expression on tubular cells, 74 fine-needle allograft aspirates (FNAB) were evaluated in 31 patients with cadaver kidney transplants. Monoclonal antibodies against T helper CD4+, cytotoxic/suppressor CD8+, and HLA-DR were used with an indirect alkaline-phosphatase-staining technique. Cases with acute rejection (n = 11) showed a significant increase of CD8+: CD4+ ratio versus those with stable function (n = 21), acute tubular necrosis (n = 10) or CsA toxicity (n = 7) (ANOVA F = 10; P less than 0.01). Cases with chronic rejection or CMV infection showed no differences in the CD8+: CD4+ ratio with the other groups. DR expression on tubular cells was frequently found in cases of acute rejection, chronic rejection and CMV (73%, 66%, and 43% respectively), occasionally found in CsA toxicity (14%), but never seen in controls or ATN. Both tests, the CD8+: CD4+ ratio and the DR expression on tubular cells, had a high sensitivity and specificity in differentiating acute rejection versus controls, acute tubular necrosis, and CsA toxicity. When both tests are taken together no case without rejection showed a CD8+:CD4+ ratio greater than 1.6 and DR expression on tubular cells. Cases with acute rejection who lost the graft (n = 6) had a CD8+:CD4+ ratio significantly greater than those who responded to antirejection therapy (n = 5) (t = 2.9; P less than 0.05).

Antibodies, Monoclonal↗
PubMed1990

Ca requirement for aerobic nitrogen fixation by heterocystous blue-green algae.

The requirement of Ca(2+) for growth and nitrogen fixation has been investigated in two strains of heterocystous blue-green algae (Anabaena sp. and Anabaena ATCC 33047). With combined nitrogen (nitrate or ammonium) or with N(2) under microaerobic conditions, Ca(2+) was not required for growth, at least in concentrations greater than traces. In contrast, Ca(2+) was required as a macronutrient for growth and nitrogen fixation with air as the nitrogen source. Addition of Ca(2+) to an aerobic culture without Ca(2+) promoted, after a lag of several hours, development of nitrogenase activity and cell growth. Provision of air to a microaerobic culture in the absence of Ca(2+) promoted a drastic drop in nitrogenase activity, which rapidly recovered its initial level upon restoration of microaerobic conditions. Development of nitrogenase activity in response to either Ca(2+) or low oxygen tension was dependent on de novo protein synthesis. The role of Ca(2+) seems to be related to protection of nitrogenase from inactivation, by conferring heterocysts resistance to oxygen.

Journal Article↗
PubMed1989

Nitrogen-fixing cyanobacterium with a high phycoerythrin content.

The elemental and molecular composition, pigment content, and productivity of a phycoerythrin-rich nitrogen-fixing cyanobacterium-an Anabaena strain isolated from the coastal lagoon Albufera de Valencia, Spain-has been investigated. When compared with other heterocystous species, this strain exhibits similar chlorophyll a, carotene, and total phycobiliprotein contents but differs remarkably in the relative proportion of specific phycobiliproteins; the content of C-phycoerythrin amounts to 8.3% (versus about 1% in the other species) of cell dry weight. Absorption and fluorescence spectra of intact phycobilisomes isolated from this Anabaena sp. corroborate the marked contribution of phycoerythrin as an antenna pigment, a circumstance that is unusual for cyanobacteria capable of fixing N(2). The pigment content of cells is affected by variations in irradiance and cell density, these adaptive changes being more patent for C-phycoerythrin than for phycocyanins. The Anabaena strain is clumpy and capable of rapid flocculation. It exhibits outdoor productivities higher than 20 g (dry weight) m day during summer.

Journal Article↗
PubMed1988

Restoration of high-potential cytochrome b-564 by integration of baker's yeast complex III into liposomes.

Cytochrome b-564 in isolated complex III from baker's yeast mitochondria exhibits the midpoint redox potential proper to the low-potential couple (+60 mV, pH 7.2). Incorporation of the complex into liposomes promotes total conversion to the high-potential couple (+170 mV, pH 7.2). The reconstituted system shows electrogenic proton translocation, which is inhibited by the uncoupler CCCP. Deenergizing treatments result, moreover, in reversal of the redox potential change. These results support our previous proposal that cytochrome b-564 acts as a transducer of redox energy into acid-base energy in the complex III region of the respiratory chain.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1988

Purification and kinetic and structural properties of spinach leaf NADP-dependent nonphosphorylating glyceraldehyde-3-phosphate dehydrogenase.

NADP-dependent nonphosphorylating D-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.9) from spinach leaves has been purified to apparent electrophoretic homogeneity by ammonium sulfate fractionation, molecular sieving on Sephadex G-200, DEAE-cellulose, and 2',5'-ADP-Sepharose affinity chromatography. The purified enzyme exhibited a specific activity of 15 mumol (mg protein)-1 min-1 and was characterized as a homotetramer with a native molecular weight of 195,000. Preincubation of the purified enzyme with NADP+ resulted in an almost twofold increase in enzymatic activity. The rate of activation was slower than the rate of catalysis, indicating that the enzyme has hysteretic properties. This behavior results in a lag phase during activity measurement of the enzyme preincubated without NADP+. Substrate interaction and product inhibition studies suggest a rapid equilibrium random BiBi mechanism for the reaction. Thiol modifying reagents, iodoacetamide and diamide, completely inactivated the purified enzyme. Inactivation by iodoacetamide exhibited pseudo-first-order kinetics with a rate constant of 0.17 min-1. D-Glyceraldehyde 3-phosphate effectively protected the enzyme against inactivation by thiol reagents, suggesting that modification occurred at or near the substrate-binding site. Complete inactivation of the dehydrogenase was correlated with incorporation of 8 mol [1-14C]iodoacetamide/mol enzyme. Total protection afforded by D-glyceraldehyde 3-phosphate against enzyme inactivation by iodoacetamide was correlated with a protection of 4 mol reactive residues/mol enzyme. On the basis of these results it is suggested that one sulfhydryl group per enzyme subunit is essential for catalysis in spinach leaf nonphosphorylating glyceraldehyde-3-phosphate dehydrogenase. A kinetic and molecular mechanism for the reaction is proposed.

Ammonium Sulfate↗
PubMed1988

Redox and acid-base characterization of cytochrome b-559 in photosystem II particles.

The redox and acid/base states and midpoint potentials of cytochrome b-559 have been determined in oxygen-evolving photosystem II (PS II) particles at room temperature in the pH range from 6.5 to 8.5. At pH 7.5 the fresh PS II particles present about 2/3 of their cytochrome b-559 in its reduced and protonated (non-auto-oxidizable) high-potential form and about 1/3 in its oxidized and non-protonated low-potential form. Potentiometric reductive titration shows that the protonated high-potential couple is pH-independent (E'0, + 380 mV), whereas the low-potential couple is non-protonated and pH-independent above pH 7.6 (E'0, pH greater than 7.6, + 140 mV), but becomes pH-dependent below this pH, with a slope of -72 mV/pH unit. Moreover, evidence is presented that in PS II particles cytochrome b-559 can cycle, according to its established redox and acid/base properties, as an energy transducer at two alternate midpoint potentials and at two alternate pKa values. Red light absorbed by PS II induces reduction of cytochrome b-559 in these particles at room temperature, the reaction being completely blocked by dichlorophenyldimethylurea.

Chlorophyll↗
PubMed1988

Action spectra for nitrate and nitrite assimilation in blue-green algae.

Action spectra for the assimilation of nitrate and nitrite have been obtained for several blue-green algae (cyanobacteria) with different accessory pigment composition. The action spectra for both nitrate and nitrite utilization by nitrate-grown Anacystis nidulans L-1402-1 cells exhibited a clear peak at about 620 nanometers, corresponding to photosystem II (PSII) C-phycocyanin absorption, the contribution of chlorophyll a (Chl a) being barely detectable. The action spectrum for nitrate reduction by a nitrite reductase mutant of A. nidulans R2 was very similar. All these action spectra resemble the fluorescence excitation spectrum of cell suspensions of the microalgae monitored at 685 nanometers-the fluorescence band of Chl a in PSII. In contrast, the action spectrum for nitrite utilization by nitrogen-starved A. nidulans cells, which are depleted of C-phycocyanin, showed a maximum near 680 nanometers, attributable to Chl a absorption. The action spectrum for nitrite utilization by Calothrix sp. PCC 7601 cells, which contain both C-phycoerythrin and C-phycocyanin as PSII accessory pigments, presented a plateau in the region from 550 to 630 nanometers. In this case, there was also a clear parallelism between the action spectrum and the fluorescence excitation spectrum, which showed two overlapped peaks with maxima at 562 and 633 nanometers. The correlation observed between the action spectra for both nitrate and nitrite assimilation and the light-harvesting pigment content of the blue-green algae studied strongly suggests that phycobiliproteins perform a direct and active role in these photosynthetic processes.

Journal Article↗
PubMed1986

[A unified concept of energy transduction by biochemical systems].

Electronic energy--resulting either from electron excitation or localization--is the obligatory link between the different forms of energy (light, redox, acid-base, metaphosphate-orthophosphate) transducible by biochemical systems. The key in energy coupling between any two transducing systems lies precisely in the fact that both of them share a common intermediate that cyclically participates in the overall transduction process by alternating between its electronically energized state and its unenergized basal state. All the energy-transducing biochemical systems must operate, according to their nature and character of the energization, at two midpoint redox potentials, at two pKa's, or at two phosphate transfer potentials. Three basic energy-transducing systems in bioenergetics, namely, redox, acid-base and metaphosphate-orthophosphate, couple between them through the acylium cation (Equation: see text)-carboxylate-anion (R-COO-) pair. These forms are, respectively, twice-energized and unenergized and can accept, at two energy levels, either two electrons or two protons or the orthophosphate anion (H2PO4-) and the "zwitterion" metaphosphate (approximately PO3-**). Both at the substrate level and at the membrane level, orthophosphate energization to metaphosphate, by removal of an oxide anion (O2-), brings about a decrease in pKa with the concomitant dissociation of the two protons (2 H+), whereas de-energization of metaphosphate to orthophosphate, by addition of an oxide anion, brings about an increase in pKa with the concomitant fixation of two protons. One of the greatest discoveries of bioenergetics was the introduction in cell metabolism of the one-electron redox photosystem chlorophyll a and was followed by the starting of the one-electron/one-proton redox/acid-base energy-transducing systems of the photosynthetic and respiratory electron transport chains.

ATP Synthetase Complexes↗
PubMed1984

Coupling between redox and acid-base energy by cytochrome b-564 in Baker's yeast mitochondria.

Baker's yeast mitochondrial cytochrome b-564 is characterized by exhibiting both a labile pH-independent high-potential form (E'o, pH 7 = + 190 mV) and a stable pH-dependent (pKa = 6.8) low-potential form (E'o, pH 7 = + 70 mV). The different behavior of these two forms of cytochrome b-564 versus pH seems to be a decisive factor for transduction of redox energy into acid-base energy in oxidative phosphorylation site 2. Deenergizing treatments, such as ADP plus Pi, result in the conversion of all the mitochondrial cytochrome b-564 into its low-potential form, whereas energization with ATP specifically transforms the cytochrome into its high-potential form, the ATP effect being neutralized by the ATPase inhibitor oligomycin and by the uncoupler FCCP. Accordingly, a minimal model for coupling between redox energy and acid-base energy through an electronically energized and protonated ferricytochrome b-564 intermediate is proposed. The energy-transducing properties of mitochondrial cytochrome b-564 seems to be shared by chloroplast cytochrome b-559.

Acid-Base Equilibrium↗