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R Serrano

Publications and source records attributed to R Serrano.

At least 127 records · Page 7Linked to original sources
PubMed1989

Sidedness of yeast plasma membrane vesicles and mechanisms of activation of the ATPase by detergents.

The binding of concanavalin A and of fluorescein 5'-isothiocyanate indicate similar amount of right-side-out and inside-out vesicles in plasma membrane vesicles from either glucose-starved or glucose-fermenting yeast cells. These vesicles contain low-activity and high-activity states of the ATPase, respectively. Unmasking of latent active sites can explain the limited ATPase activation (about 2-fold) produced by several detergents on both kinds of vesicles. On the other hand, lysophosphatidic acid (oleoyl) produces a 7-fold activation of the ATPase in vesicles from glucose-starved cells. This effect is accompanied by a change in Km of the enzyme and probably reflects a direct action of the detergent on the ATPase. A similar activation and Km change can be obtained by sonication of the vesicles, although in this case soybean phospholipids are required for maximal activity. Apparently the low-activity state of the yeast plasma membrane ATPase can be activated not only by glucose metabolism 'in vivo' (mechanism unknown) but also by some detergents and physical treatments 'in vitro'. Experiments with purified ATPase from glucose-starved cells also indicate that lysophosphatidic acid (oleoyl) specifically activates the enzyme. These results suggest a note of caution on considering the usual interpretation of the effects of detergents on membrane enzymes, which only take into account the unmasking of latent active sites.

Adenosine Triphosphatases↗
PubMed1989

Structure of a plasma membrane H+-ATPase gene from the plant Arabidopsis thaliana.

Physiological and biochemical studies have suggested that the plant plasma membrane H+-ATPase controls many important aspects of plant physiology, including growth, development, nutrient transport, and stomata movements. We have started the genetic analysis of this enzyme by isolating both genomic and cDNA clones of an H+-ATPase gene from Arabidopsis thaliana. The cloned gene is interrupted by 15 introns, and there is partial conservation of exon boundaries with respect to animal (Na+/K+)- and Ca2+-ATPases. In general, the relationship between exons and the predicted secondary and transmembrane structure of different ATPases with phosphorylated intermediate support a somewhat degenerate correspondence between exons and structural modules. The predicted amino acid sequence of the plant H+-ATPase is more closely related to fungal and protozoan H+-ATPases than to bacterial K+-ATPases or to animal (Na+/K+)-, (H+/K+)-, and Ca2+-ATPases. There is evidence for the existence of at least three isoforms of the plant H+-ATPase gene. These results open the way for a molecular approach to the structure and function of the plant proton pump.

Amino Acid Sequence↗
PubMed1989

[Incidence of nosocomial infections. Comparison of 2 surveillance systems: clinical vs microbiological follow-up].

The effectiveness of a clinical and a microbiological follow-up systems for the detection of hospital-acquired infection (HI), both independently and simultaneously applied, were prospectively evaluated. The observed incidence rate was 11.4%. The clinical follow-up detected 81.3% of HI while microbiological follow-up detected 59.7%. This difference was statistically significant (p less than 0.001). It took 43 and 45 minutes to detect each instance of HI with the clinical and microbiological methods, respectively. Clinical methods are the most adequate to obtain maximal sensitivity in the overall surveillance of hospital-acquired infection, whereas microbiological follow-up may be useful for the detection of some types of HI such as bacteremia or urinary tract infection.

Cohort Studies↗
PubMed1989

Deletion analysis of yeast plasma membrane H+-ATPase and identification of a regulatory domain at the carboxyl-terminus.

The function of the amino- and carboxyl-terminal domains of the yeast plasma membrane H+-ATPase have been investigated by constructing deletions in vitro and selectively expressing the mutant enzymes in vivo. The first 27 amino acids are dispensable but deletion of a further 33 amino acids greatly decreases the appearance of the enzyme in the plasma membrane. Membrane localization is also prevented by carboxyl-terminal deletions which include the last hydrophobic stretch, but the last 46 amino acids of the ATPase are not required. Removal of the last 11 amino acids produces an enzyme in glucose-starved cells with the kinetic parameters of the wild-type ATPase activated by glucose fermentation. This region seems to constitute a regulatory domain.

Amino Acid Sequence↗
PubMed1989

Identification of a tumour factor inducing resistance to NK cell lysis.

The mechanisms involved in the resistance or susceptibility of tumour cells to NK cytotoxicity are poorly understood. The role of different molecules on the target cell surface which could act as recognition elements by NK effectors has been postulated. However, there are also some tumour cell lines which release factors capable of inhibiting NK cytotoxicity. This paper presents a new factor (NK-RIF), produced and released by different tumour cell lines, making K562 resistant to NK lysis without affecting the cytotoxic function of NK effector cells. This soluble factor is shown to be thermolabile, non-dialyzable and to have a molecular weight of 36,000 daltons. It does not block the binding capacity of the target and effector cells, nor does it affect target susceptibility to LAK or cytotoxic T-cells.

Adenocarcinoma↗
PubMed1989

Natural killer susceptibility of brain tumor cell lines inversely correlates with the degree of cell differentiation and not with the level of human histocompatibility antigen expression.

The purpose of this paper is to investigate the natural killer (NK) sensitivity of 15 cell lines derived from human brain tumors expressing different levels of major histocompatibility complex (MHC) antigens. Although it has recently been reported that NK susceptibility varies inversely with target cell class-I human leukocyte antigen (HLA) expression, our results show no correlation between class-I HLA, class-II HLA or beta 2-microglobulin expression on target cells and NK sensitivity, whereas a significant inverse correlation between NK susceptibility and the degree of tumor cell differentiation has been found. Thus, poorly differentiated tumor cells are highly susceptible to NK lysis, whereas well-differentiated ones are NK resistant. These results suggest that sensitivity to lysis by NK cells of cell lines derived from human brain tumors is primarily determined by the stage of differentiation and not by the level of MHC antigen expression on target cell.

Brain Neoplasms↗
PubMed1989

[Trichinosis: new epidemic outbreak caused by the ingestion of wild-boar sausage].

After the evaluation of 129 serum samples of persons who had ingested boar sausage infested by Trichinella spiralis, 48 individuals (40 adults and 8 children) with a mean age of 38.8 years were diagnosed of trichinosis. The incubation time was 17 days (range 2 to 44 days). The following clinical features were outstanding: facial and eyelid edema (50%), diffuse limb myalgia (43%), fever (37%), conjunctivitis (25%), headache (16%), and abdominal pain (16%). Remarkably, 33% of the diagnosed patients were asymptomatic. The diagnosis was made by an indirect immunofluorescence technique (IIF), which was considered as positive when the titer was higher than 1/20 after considering seroconversion at the beginning of the disease and after 4-6 weeks. Among laboratory abnormalities there was leukocytosis in 15 patients and eosinophilia in 37. The GOT, GPT and CPK enzymes were only slightly increased in a small proportion of patients (8, 10, and 31%, respectively). Forty patients were treated with thiabendazole, associated or not to corticosteroids, which was well tolerated. Eight patients were not treated. One year after the diagnosis a new laboratory control was undertaken in 43 patients (all asymptomatic). Eosinophilia was still present in 12, and the titers against Trichinella were high in all. However, the percentage of the titer was smaller than at the beginning of the outbreak.

Adrenal Cortex Hormones↗
PubMed1988

Mutations of the yeast plasma membrane H+-ATPase which cause thermosensitivity and altered regulation of the enzyme.

Four random mutations of the plasma membrane H+-ATPase of Saccharomyces cerevisiae which result in thermosensitive growth have been sequenced. All of the mutations map in regions conserved by the family of ATPases which form a phosphorylated intermediate. The Gly254----Ser mutation affects a glycine residue conserved in all of the sequenced ATPases. The Thr212----Ile and Ala547----Val mutations do not affect conserved amino acids, but their replacements are not found in any of the sequenced ATPases. Thr212 and Gly254 occur in the proposed phosphatase domain, whereas Ala547 is located within the putative ATP-binding site. The other mutation is a double change (Asp91----Tyr and Glu92----Lys) in the N-terminal domain, in which the altered glutamate is conserved in fungal and protozoan H+-ATPases. Proton efflux from whole cells and ATP hydrolysis by purified plasma membranes are more thermolabile in cells carrying the ATPase mutations than in wild-type yeast. Therefore, the defects in growth and proton transport at the nonpermissive temperature can be attributed to impairment of ATPase activity. Incubation of wild-type yeast cells with glucose before homogenization induces changes in the specific activity, Km, pH optimum, and vanadate sensitivity of the plasma membrane ATPase. The Ala547----Val mutation results in an enzyme from starved cells with the kinetic parameters of the glucose-activated wild-type ATPase. Therefore, a single amino acid change mimics the poorly understood regulatory mechanism triggered by glucose.

Amino Acid Sequence↗
PubMed1988

Increased pH and tumorigenicity of fibroblasts expressing a yeast proton pump.

A common early response of eukaryotic cells to stimuli which activate their proliferation is an increase in intracellular pH (ref. 1). In animal cells this is caused by the activation of an Na+/H+ exchange system; in fungi and plants an H+-pumping ATPase is involved. The critical question is whether this intracellular alkalinization is merely coincident with the activation of cell proliferation or whether it is a regulatory signal. To increase intracellular pH bypassing the usual physiological stimuli (growth factors, hormones etc.) alkaline media or ammonia have been used in the past. Both approaches suffer from long-term toxicity effects and cannot be used in tumorigenic assays with whole organisms. We introduce here a more specific approach which involves expressing the gene for the yeast plasma membrane H+-ATPase in fibroblasts. The resulting cells have an elevated intracellular pH and acquire tumorigenic properties, suggesting that the yeast ATPase gene behaves as an oncogene in mammalian cells. These experiments support a crucial role of intracellular pH in the growth control of animal cells.

Cell Transformation, Neoplastic↗
PubMed1988

Dissection of functional domains of the yeast proton-pumping ATPase by directed mutagenesis.

Cation-pumping ATPases characterized by a phosphorylated intermediate have been proposed to contain kinase, phosphatase and transduction domains. Evidence is provided for this model by mutagenesis of critical residues in the proposed domains. The Glu233-Gln mutation blocks the turnover of the intermediate and serves to define the phosphatase domain. Mutations in aspartate residues 534, 560 and 638 alter the nucleotide specificity of the enzyme. These amino acids are therefore part of the ATP binding site. Lys474 seems to be essential for activity in this kinase domain. Finally, mutations in Asp378, the amino acid forming the phosphorylated intermediate, indicate that the formation of a phosphorylated intermediate is not an obligatory step in ATP hydrolysis but is required for coupling this process with proton pumping.

Adenosine Triphosphate↗
PubMed1987

Tight control of the amount of yeast plasma membrane ATPase during changes in growth conditions and gene dosage.

The activity of the plasma membrane ATPase in growing yeast is increased by low pH and by glucose, conditions which result in a higher demand for proton pumping. The amount of enzyme is not significatively modified under these conditions. The amount of ATPase is only slightly increased by introducing extra copies of its gene in autonomous plasmids. In addition, the expression of the ATPase gene in a multi-copy plasmid causes a reduction of the copy number of the plasmid and slows growth. Therefore, overexpression of the ATPase is detrimental for the cell, justifying a regulatory mechanism based on increasing the catalytic activity and not the amount of enzyme.

Adenosine Triphosphatases↗