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A Cabezas

Publications and source records attributed to A Cabezas.

12 recordsLinked to original sources
PubMed2002

Sludge bed development in denitrifying reactors using different inocula-performance and microbiological aspects.

Aerobic and methanogenic consortia were evaluated as inocula for laboratory scale denitrifying reactors, fed with a synthetic wastewater with acetate as the main electron donor. The denitrifying microflora of inocula and reactors was evaluated by specific denitrifying activity, enumeration and isolation of denitrifiers, which were screened by amplified ribosomal DNA restriction analysis. Reactor performance was monitored by COD and nitrate removal efficiencies and granule size. The aerobic sludge failed to form granules, probably due to the development of a filamentous, nitrate-reducing organism which was characterised by 16SrDNA sequencing as Bacillus cereus. The methanogenic sludge showed denitrifying activity and adapted very rapidly to denitrifying conditions in the two reactors seeded with granules of different sizes. Denitrifiers grew around the granules, increasing the specific denitrifying activity of the sludge over 10-fold. Exopolymer-forming organisms, belonging to the same species, were isolated from both reactors. Granule size increased during operation, but flotation of the aggregates, related to gas retention was observed.

Acetates↗
PubMed2001

Purification, characterization, and substrate and inhibitor structure-activity studies of rat liver FAD-AMP lyase (cyclizing): preference for FAD and specificity for splitting ribonucleoside diphosphate-X into ribonucleotide and a five-atom cyclic phosphodiester of X, either a monocyclic compound or a cis-bicyclic phosphodiester-pyranose fusion.

An enzyme with FAD-AMP lyase (cyclizing) activity, splitting FAD to AMP and riboflavin 4',5'-phosphate (cFMN), was recently identified [Fraiz, F., et al. (1998) Biochem. J. 330, 881-888]. Now, it has been purified to apparent homogeneity from a rat liver supernatant, by a procedure that includes affinity for ADP-agarose (adsorption required the activating cation Mn2+ and desorption required its removal), to a final activity of 2.2 units/mg after a 240-fold purification with a 15% yield. By SDS-PAGE, only one protein band was observed (Mr = 59 000). The correspondence between protein and enzyme activity was demonstrated by renaturation after SDS-PAGE, by gradient ultracentrifugation followed by analytical SDS-PAGE, and by native PAGE with visualization of enzyme activity by fluorescence. A native Mr of 100 000 (ultracentrifugation) or 140 000 (gel filtration) indicated that FAD-AMP lyase could be a dimer. The enzyme required millimolar concentrations of Mn2+ or Co2+, exhibited different optimum pH values with these cations (pH 8.5 or 7.3, respectively), and was strongly inhibited by ADP or ATP, but not by dADP, dATP, or the reaction products AMP and cFMN. A specificity study was conducted with 35 compounds related to FAD, mostly nucleoside diphosphate-X (NDP-X) derivatives. Besides FAD, the enzyme split 11 of these compounds with the pattern NDP-X --> NMP + P=X. Structure-activity correlations of substrates, nonsubstrates, and inhibitors, and the comparison of the enzymic reactivities of NDP-X compounds with their susceptibilities to metal-dependent chemical degradation, pinpointed the following specificity pattern. FAD-AMP lyase splits ribonucleoside diphosphate-X compounds in which X is an acyclic or cyclic monosaccharide or derivative bearing an X-OH group that is able to attack internally the proximal phosphorus with the geometry necessary to form a P=X product, either a five-atom monocyclic phosphodiester or a cis-bicyclic phosphodiester-pyranose fusion. For instance, NDP-glucose and GDP-alpha-L-fucose were substrates, but dTDP-glucose, NDP-mannose, and GDP-beta-L-fucose were not. Judging from kcat/Km ratios, we found the best substrate to be FAD, followed closely by ADP-glucose (kcat/Km only 2-fold lower, but not a physiological compound in mammals), whereas other substrates exhibited 50-500-fold lower kcat/Km values. However, there was no evidence for specific flavin recognition. Instead, what seems to be recognized is the NDP moiety of NDP-X, with a strong preference for ADP-X. Splitting would then depend on the presence of an adequate X-OH group. The possibility that, besides FAD, there could be in mammals other ADP-X substrates of FAD-AMP lyase is discussed, with emphasis placed on some ADP-ribose derivatives.

Adenosine Diphosphate↗
PubMed2000

The simulated purification of an enzyme as a 'dry' practical within an introductory course of biochemistry.

This article describes a 'dry-laboratory' practical in which the multi-step purification of an enzyme is simulated. It has been devised to be implemented with beginner undergraduates taking an introductory course in biochemistry, with the aim of giving them a glimpse of the intensity of effort involved in complex, research-oriented experiments. The purification steps simulated are: preparation of a liver soluble extract, ammonium sulfate fractionation, gel filtration, ion-exchange and dye-ligand affinity chromatography. Before the simulation, our students are familiar with the preparative and analytical techniques involved, through short 'cookbook' laboratory experiments and, in some cases, ad hoc demonstrations. For the simulation, the students are given detailed protocols of the preparative and analytical experiments, and the raw numeric or graphical data obtained. They have to perform the calculations and graphing necessary to produce a purification table. The 27-page Student Booklet needed to implement the practical is offered by the authors to interested teachers, as a printable electronic file.

Journal Article↗
PubMed1998

Enzymic formation of riboflavin 4',5'-cyclic phosphate from FAD: evidence for a specific low-Km FMN cyclase in rat liver1.

An enzyme activity splitting FAD to AMP and riboflavin 4',5'-cyclic phosphate (4',5'-cFMN), with a Km of 6-8 microM, was partially purified from the cytosolic fraction of rat liver homogenates. 4', 5'-cFMN was characterized by enzyme, HPLC, UV-visible and NMR spectroscopic analyses. The data suggest that a novel enzyme, tentatively named FAD-AMP lyase (cyclizing) or FMN cyclase, is involved. Also, 4',5'-cFMN was hydrolysed to 5'-FMN by a rat liver cyclic phosphodiesterase. The results indicate a novel enzymic pathway for flavins in mammals, and support the biological relevance of 4',5'-cFMN, perhaps as a flavocoenzyme or a regulatory signal.

Adenosine Monophosphate↗
PubMed1996

[Chylopericardium after acute pericarditis].

We present an 18 year-old man with chylopericardium after acute pericarditis with severe pericardial effusion and cardiac tamponade secondary to Mycoplasma pneumoniae infection. We review the etiology, diagnostic procedures and therapeutic possibilities for chylopericardium.

Acute Disease↗
PubMed1995

Immunological aspects of a case of posttransplant lymphoproliferative disorder.

We describe a female renal transplant recipient with cytomegalovirus and Epstein-Barr virus (EBV) infections who developed aggressive polymorphous polyclonal B cell proliferation. She received two courses of OKT3. We found a majority of transformed B cells bearing EBV membrane receptor CR2 and EBV nuclear antigen. Posttransplant lymphoproliferative disorders may be associated with a significant immunological activation, detected in this case by the sudden increase of beta 2-microglobulin and immunoglobulin levels, including immunoglobulin D. These raised levels persisted throughout the short and rapid course of the disease.

Adult↗
PubMed1978

Induction of ovulation with clomiphene and estradiol benzoate in anovulatory women refractory to clomiphene alone.

Twenty-two infertile and clomiphene-nonresponding patients received a course of clomiphene, 100 mg/day for 5 days, followed 7 days later by an intramuscular injection of 1 mg of estradiol benzoate. The diagnosis of idiopathic chronic anovulation had been established. None of these patients had galactorrhea, hirsutism, or ovarian enlargement. Thirteen of the twenty-two women had surges of both luteinizing hormone and follicle-stimulating hormone after the estradiol injection; the peak gonadotropin levels occurred within 72 hours of the injection. These 13 patients ovulated and pregnancy ensued in 10 of them. The estradiol benzoate injection also elicited a significant increase in serum prolactin levels- This enhanced prolactin release had no apparent effect on the gonadotropin surge. These results suggest that the association of clomiphene and estradiol benzoate potentiates the action of clomiphene and may prove useful in clomiphene nonresponders.

Adult↗
PubMed1977

Gonadotropic responsiveness to clomiphene, LRH, estradiol, and bromocriptine in galactorrheic women.

Twenty hyperprolactinemic patients with galactorrhea were studied to determine their gonadotropic responses to various stimuli. Five women lacked response to gonadotropin following the administration of clomiphene citrate. Ten patients who had luteinizing hormone releasing hormone (LRH) tests before and during bromocriptine administration exhibited varied FSH and LH responses that apparently were unaffected by bromocriptine therapy. A loss of the normal positive feedback of estrogens at the level of the hypothalamus was demonstrated in most patients before and during bromocriptine therapy. Long-term treatment with bromocriptine in 11 women resulted in a decrease of serum prolactin, cessation of lactation in all, and pregnancy in 8. These results suggest that the failure of normal secretion of gonadotropins in hyperprolactinemic women may result from 1) inadequate release of endogenous LRH, and 2) loss of the positive feedback of estrogens, as a result of the same hypothalamic disturbance that provokes the hyperprolactinemia. In turn, the elevated prolactin levels may exert a short-loop negative feedback at the hypothalamic level, inhibiting cyclic gonadotropin release.

Bromocriptine↗
PubMedDate not supplied

Heterogeneous pituitary secretion in familial hypogonadotropic hypogonadism.

Dynamic testing of the hypothalamic pituitary system in familial hypogonadotropic hypogonadism has suggested the possibility of a central nervous disorder associated with variable pituitary secretory secretion. In order to investigate this issue further 7 patients of two families were studied. Male patients exhibited two types of FSH responses to LHRH administration. Two patients had a small response, and the other exhibited a normal response. The LH response was absent or small in both male and female patients. One month therapy with daily injections of LHRH did not improve pituitary responsiveness to a second LHRH test. Estrogen treatment given to females during one month had no improvement effect on another LHRH test. Estradiol benzoate produced a surge in both LH and FSH in half of patients tested which is surprising in the presence of a previous clomiphene negative response. Two of four women had elevated prolactin levels which increased defectuously after metoclopramide administration which could suggest an abnormal hypothalamic status. On the basis of these results it seems that familial hypogonadotropism is originated by an abnormality at two levels, the anterior pituitary and the hypothalamus as well.

Adolescent↗