Biomedical subjects

E Andújar

Publications and source records attributed to E Andújar.

6 recordsLinked to original sources

PubMed2001

The distal convoluted tubule of rabbit kidney does not express a functional sodium channel.

We sought to assess whether the distal convoluted tubule (DCT) segment of the rabbit nephron expresses a functional epithelial sodium channel. First, the transepithelial voltage (V(te), lumen vs. bath) was measured in isolated perfused DCT segments (assessed separately in the upstream half and the downstream half of the DCT). V(te) was zero and not affected by amiloride or barium in the upstream DCT. V(te) was sometimes negative in the downstream DCT and depolarized by amiloride and hyperpolarized by barium, suggesting inclusion of connecting tubule (CNT) cells. To determine expression of epithelial sodium channel (ENaC) mRNA subunits by the upstream DCT, rabbit alpha-, beta-, and gamma-ENaC cDNA fragments were cloned and primers were selected for single-nephron RT-PCR analysis. Although alpha-ENaC was expressed by the DCT, beta- and gamma-ENaC were not detected in the DCT. In contrast, the CNT, CCD, and outer medullary collecting duct (OMCD) expressed all three subunits. Nedd4 was also not detected in the DCT but was expressed by the CNT, CCD, and OMCD. When upstream DCT fragments were grown to confluent monolayers in primary culture, the epithelia exhibited negative voltages and high transepithelial resistances and expressed mRNA for all three ENaC subunits as well as for Nedd4. The absence of a negative voltage and failure to detect transcript for beta- and gamma-ENaC and Nedd4 in the native rabbit DCT suggest that the sodium channel is not a significant pathway for sodium absorption by this segment. The phenotype conversion observed when DCT cells are grown in culture does not rule out the possibility that there may be conditions in which the DCT in the intact kidney expresses sodium channel activity. The results are consistent with the notion that DCT sodium transport is predominantly, if not exclusively, electroneutral.

Animals↗

PubMed2000

Identification of a serine hydrolase which cleaves the alicyclic ring of tetralin.

A gene designated thnD, which is required for biodegradation of the organic solvent tetralin by Sphingomonas macrogoltabidus strain TFA, has been identified. Sequence comparison analysis indicated that thnD codes for a carbon-carbon bond serine hydrolase showing highest similarity to hydrolases involved in biodegradation of biphenyl. An insertion mutant defective in ThnD accumulates the ring fission product which results from the extradiol cleavage of the aromatic ring of dihydroxytetralin. The gene product has been purified and characterized. ThnD is an octameric thermostable enzyme with an optimum reaction temperature at 65 degrees C. ThnD efficiently hydrolyzes the ring fission intermediate of the tetralin pathway and also 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid, the ring fission product of the biphenyl meta-cleavage pathway. However, it is not active towards the equivalent intermediates of meta-cleavage pathways of monoaromatic compounds which have small substituents in C-6. When ThnD hydrolyzes the intermediate in the tetralin pathway, it cleaves a C-C bond comprised within the alicyclic ring of tetralin instead of cleaving a linear C-C bond, as all other known hydrolases of meta-cleavage pathways do. The significance of this activity of ThnD for the requirement of other activities to mineralize tetralin is discussed.

Bacterial Proteins↗

PubMed2000

Identification of an extradiol dioxygenase involved in tetralin biodegradation: gene sequence analysis and purification and characterization of the gene product.

A genomic region involved in tetralin biodegradation was recently identified in Sphingomonas strain TFA. We have cloned and sequenced from this region a gene designated thnC, which codes for an extradiol dioxygenase required for tetralin utilization. Comparison to similar sequences allowed us to define a subfamily of 1, 2-dihydroxynaphthalene extradiol dioxygenases, which comprises two clearly different groups, and to show that ThnC clusters within group 2 of this subfamily. 1,2-Dihydroxy-5,6,7, 8-tetrahydronaphthalene was found to be the metabolite accumulated by a thnC insertion mutant. The ring cleavage product of this metabolite exhibited behavior typical of a hydroxymuconic semialdehyde toward pH-dependent changes and derivatization with ammonium to give a quinoline derivative. The gene product has been purified, and its biochemical properties have been studied. The enzyme is a decamer which requires Fe(II) for activity and shows high activity toward its substrate (V(max), 40.5 U mg(-1); K(m), 18. 6 microM). The enzyme shows even higher activity with 1, 2-dihydroxynaphthalene and also significant activity toward 1, 2-dihydroxybiphenyl or methylated catechols. The broad substrate specificity of ThnC is consistent with that exhibited by other extradiol dioxygenases of the same group within the subfamily of 1, 2-dihydroxynaphthalene dioxygenases.

Dioxygenases↗

PubMed1998

Mechanism of translational coupling in the nifLA operon of Klebsiella pneumoniae.

The nifLA operon of Klebsiella pneumoniae encodes the sensor-activator pair involved in the regulation of other nif genes. Balanced synthesis of both proteins, which is required for correct regulation, is achieved by coupling translation of nifA to that of nifL. The mechanism of translational coupling at the nifLA operon was analysed using a specialized ribosome system, and the effect of substituting the natural Shine-Dalgarno of nifL or nifA for specialized Shine-Dalgarno sequences was determined. Our results indicate that translational coupling occurs in this operon by a reinitiation mechanism. Additionally, reinitiation at the nifA can happen even in the absence of good Shine-Dalgarno recognition by the reinitiating ribosome, although its efficiency is lower. The effect of a putative translational enhancer sequence (downstream box) on translational coupling efficiency was also determined. Mutations that reduce the homology of the putative downstream box to the consensus had only a minor effect on nifA translation by wild-type ribosomes. However, they had a significant effect on nifA translation by specialized ribosomes, suggesting that recognition of the downstream box may compensate inefficient ribosomal interactions with the Shine-Dalgarno sequence.

Bacterial Proteins↗

PubMed1998

Rabbit distal convoluted tubule coexpresses NaCl cotransporter and 11 beta-hydroxysteroid dehydrogenase II mRNA.

BACKGROUND: Although the renal cortical collecting duct (CCD) is a principal target for aldosterone, recent evidence suggests that salt transport by other nephron segments may also be regulated by aldosterone. Electroneutral and thiazide-sensitive NaCl cotransport by the distal convoluted tubule (DCT) of the rat is increased in animals deprived of dietary NaCl. We tested the hypothesis that the DCT of the rabbit is an aldosterone target tissue. METHODS: The single-nephron reverse-transcriptase/polymerase chain reaction (RT-PCR) technique was used to determine mRNA expression of NaCl cotransporter and 11 beta-HSD 2 in dissected nephron segments. The rabbit NaCl cotransporter was first cloned and rabbit-specific primers selected. A micro-assay was developed to assess 11 beta-HSD 2 enzyme activity in 0.5 mm samples of the same nephron segments. RESULTS: NaCl cotransporter was expressed in 0 of 6 proximal tubule (PT), 6 of 6 DCT and 3 of 6 CCD samples, while 11 beta-HSD was found in 0 of 7 PT, 7 of 7 DCT and 9 of 9 CCD samples. Corticosterone was converted to 11-dehydrocorticosterone at a high rate and to a similar extent by both the DCT and CCD, but not the PT. CONCLUSIONS: We conclude that the DCT is a target tissue for the action of aldosterone. Axial heterogeneity of electroneutral (in DCT) and electrogenic (in CCD) Na transporters along the distal nephron may improve sodium recovery in low salt and volume states.

11-beta-Hydroxysteroid Dehydrogenases↗

PubMedDate not supplied

[Petit mal in children].

Thirty-two cases of children with petit mal were reviewed, finding that it is an entity of low frequency among the group of epileptic disorders; also there is no differences between sexes. The prognosis has become worsening by the presence of other types of crises, abnormal neurological examination, subnormal intelligence, behavior disorders and an "atypica", EEG. It is also influenced by the beginning of therapy at the pubertal development time. Ethosuximide seems to be the drug of choice in the "uncomplicated" cases.

Adolescent↗