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Biomedical subjects

H Nelson

Publications and source records attributed to H Nelson.

At least 127 records · Page 7Linked to original sources
PubMed1993

Vacuolar ATPase mutants accumulate precursor proteins in a pre-vacuolar compartment.

The vacuole of the yeast Saccharomyces cerevisiae contains a proton-translocating ATPase that acidifies the vacuolar lumen and generates an electrochemical potential across the vacuole membrane. Strains with chromosomal disruptions of the genes encoding the A, B, and c subunits of the vacuolar ATPase accumulate precursor forms of the vacuolar membrane protein alkaline phosphatase, and the soluble vacuolar hydrolases carboxypeptidase Y and proteinase A. We have found that the intracellular precursors in delta vat strains accumulate within the secretory pathway at some point before delivery to the vacuole but after transit to the Golgi complex. Purified vacuoles from delta vat cells do not contain the precursor forms of carboxypeptidase Y or alkaline phosphatase. In addition, vacuolar hydrolase-invertase hybrid proteins are inefficiently delivered to the vacuole in delta vat strains as demonstrated by vacuole isolation. Further subcellular fractionation to separate organelles indicate that significant amounts of the carboxypeptidase Y-invertase and alkaline phosphatase-invertase hybrid proteins are located in the late Golgi complex and/or post Golgi compartments.

Alkaline Phosphatase↗
PubMed1993

Molecular characterization of four pharmacologically distinct gamma-aminobutyric acid transporters in mouse brain [corrected].

Two novel gamma-aminobutyric acid (GABA) transporters, GAT3 and GAT4, were cloned from the mouse neonatal brain cDNA library and expressed in Xenopus oocytes. Sequence analysis indicated they were members of the Na(+)-dependent neurotransmitter transporter family. The GABA uptake activities were measured in cRNA injected Xenopus oocytes. The Km for GABA uptake by GAT3 was 18 microM and by GAT4 was 0.8 microM. GAT3 also transports beta-alanine and taurine with Km of 28 and 540 microM, respectively. Similarly, GAT4 transports beta-alanine with Km of 99 microM and taurine with a Km of 1.4 mM. The newly cloned GABA transporters were compared with two previously cloned GABA transporters, GAT1 and GAT2, in terms of molecular and pharmacological properties. While GAT1 and GAT4 gene expression were neural specific, GAT2 and GAT3 mRNAs were detected in other tissues such as liver and kidney, in which GAT3 mRNA was especially abundant. The expression of GAT3 mRNA in mouse brain is developmentally regulated, and its mRNA is abundant in neonatal brain but not in adult brain. High affinity GABA transporters GAT1 and GAT4 were more sensitive to inhibition by nipecotic acid. Low affinity GABA transporters GAT2 and GAT3 were inhibited most effectively by betaine and beta-alanine, respectively. The differential tissue distribution and distinct pharmacological properties of those four GABA transporters suggest functional specialization in the mechanisms of GABA transmission termination.

Amino Acid Sequence↗
PubMed1993

A rat brain cDNA encoding the neurotransmitter transporter with an unusual structure.

A rat cDNA clone encoding the novel membrane protein of the neurotransmitter transporters family was cloned and sequenced. The cDNA was identified as a transcript of the gene NTT4 of which a partial genomic clone was previously sequenced. Alignment of the amino acid sequence of NTT4 with other members of the neurotransmitter transporter family revealed a marked deviation from the conserved structure of all other members of the family. The largest extracellular loop with a potential glycosylation site was identified between membrane segments 7 and 8. The protein retains the common glycosylated loop between transmembrane helices 3 and 4 in all members of the family. The transcript of NTT4 was found exclusively in the central nervous system and is more abundant in the cerebellum and the cerebral cortex.

Amino Acid Sequence↗
PubMed1993

Radiation injuries of the colon and rectum.

Approximately 5% to 10% of patients receiving abdominopelvic radiation therapy will develop a colon or rectal injury. Thorough evaluation of the patient to determine the extent of the injury and the presence of concomitant lesions and to rule out recurrent malignancy is urged. Many radiation complications can be managed with medical regimens. Although colostomy remains a valuable and frequently utilized mode of treatment, it is by no means the sole alternative when surgical intervention is required. Rectal resection with colorectal or coloanal anastomosis can be performed safely for some injuries involving the distal rectum. Surgery for irradiated bowel should be focused on minimizing dissection to minimize injuries and on providing healthy non-irradiated tissues to provide adequate blood supply to promote healing. Patients who have received abdominopelvic radiation are at greater risk of developing colorectal cancer, and cancer surveillance should be commenced 5 years after completion of therapy.

Colonic Diseases↗
PubMed1993

[Sexual function after ileo-anal anastomosis].

After restorative proctocolectomy, both men and women report an improved sexual life primarily because of a better general health. Sexual dysfunction has been reported by a few men who complain of lack of or retrograde ejaculation (2%) or impotence (3%). Sexual dysfunction, especially dyspareunia, can persist in as many as 20% of women after ileoanal anastomosis, but is less severe than preoperatively in most and is less common than after ileostomy, whether continent or not. Women with an ileal pouch-anal anastomosis can conceive, and have had successful deliveries, either vaginally or by cesarean section, without long-term detrimental effects on ileal reservoir function. Indeed, stool frequency increased and continence worsened in a small group of ileoanal anastomosis women but the changes were minimal and returned to predelivery status 3 months after delivery.

Adenomatous Polyposis Coli↗
PubMed1992

Cloning and expression of a cDNA encoding the transporter of taurine and beta-alanine in mouse brain.

A taurine/beta-alanine transporter was cloned from a mouse brain cDNA library by screening with a partial cDNA probe of the glycine transporter at low stringency. The deduced amino acid sequence predicts 590 amino acids with typical characteristics of the sodium-dependent neurotransmitter transporters such as sequence homology and membrane topography. However, the calculated isoelectric point of the taurine/beta-alanine transporter is more acidic (pI = 5.98) than those (pI > 8.0) of other cloned neurotransmitter transporters. Xenopus oocytes injected with cRNA of the cloned transporter expressed uptake activities with Km = 4.5 microM for taurine and Km = 56 microM for beta-alanine. Northern hybridization showed a single transcript of 7.5 kilobases that was highly enriched in kidney and distributed evenly in various parts of the brain. In situ hybridization showed the mRNA of the taurine/beta-alanine transporter to be localized in the corpus callosum, striatum, and anterior commisure. Specific localization of the taurine/beta-alanine transporter in mouse brain suggests a potential function for taurine and beta-alanine as neurotransmitters.

Amino Acid Sequence↗
PubMed1992

Cloning and expression of the bovine cardiac sodium-calcium exchanger.

Two clones (p17 and p13), each containing the complete coding sequence for the bovine cardiac Na+/Ca2+ exchanger, were obtained from a lambda gt10 cDNA library by screening with cDNA probes from the canine exchanger. The coding sequence of clone p17 was 92 and 98% identical to the canine cDNA at the nucleotide and amino acid levels, respectively. Nine of the 21 amino acid differences between the two exchangers were found within the 32-amino acid signal sequence. The sequenced portions of the 3' untranslated regions of the cow and dog clones were 88% identical. Na+/Ca2+ exchange activity was expressed in Xenopus laevis oocytes injected with cRNA from clone p17, and in COS cells transfected with expression vectors containing p17. Immunoprecipitation of 35S-labeled proteins from transfected cells with an antibody against the N-terminal portion of the bovine exchanger showed the presence of a 120-kDa protein corresponding to the intact cardiac exchanger. The second bovine clone (p13) did not express exchange activity in either of the above expression systems, presumably because it contained a 300-bp insert with multiple stop codons which interrupted the coding sequence. Comparison of the 5' untranslated regions of p13 and p17 revealed a 156-bp segment in p17 that was apparently spliced out of p13. This segment contained a short open reading frame. A chimera encoding the 5' untranslated region of p13 and the coding sequence of p17 exhibited only a modest (74%) increase in expressed exchange activity in transfected cells compared to p17, suggesting that the presence of the upstream open reading frame in p17 did not greatly reduce translation efficiency. The results suggest that alternate splicing mechanisms may be involved in processing mRNA for the bovine cardiac exchanger.

Amino Acid Sequence↗
PubMed1992

Expression of a mouse brain cDNA encoding novel gamma-aminobutyric acid transporter.

A nipecotic acid-resistant gamma-aminobutyric acid (GABA) transporter was cloned from a mouse brain cDNA library. The 2.3-kilobase cDNA clone contains an open reading frame of 1842 nucleotides encoding a protein of 614 amino acids. The predicted amino acid sequence indicates it is a member of the gene family of the sodium-dependent neurotransmitter transporters. The new GABA transporter, named GAT2, is highly homologous to the betaine transporter (BGT1) cloned from canine kidney. However, GAT2 expression in the brain distinguished it from BGT1 which was exclusively expressed in the kidney. The transcripts of GAT2 were found in the cerebral cortex, cerebellum, and brainstem as well as in kidney. Expression of GAT2 in Xenopus oocytes revealed a Km of 79 microM for GABA uptake which is about 10-fold higher than that of the high affinity GABA transporter (GAT1). The pharmacology of GAT2 is different from that of GAT1 because of lack of inhibition by guvacine and nipecotic acid and sensitivity to high concentrations of betaine and beta-alanine. GAT2 transports betaine with a Km of about 200 microM, but no significant transport of beta-alanine could be detected. The presence of mRNA encoding GAT2 in parts of the brain suggests it is a neurotransmitter transporter.

Amino Acid Sequence↗
PubMed1992

Photosynthetic reaction center genes in green sulfur bacteria and in photosystem 1 are related.

Oxygenic photosynthesis of chloroplasts and cyanobacteria involves two photosystems, which originate from different prokaryotic ancestors. The reaction center of photo-system 2 (PS2) is related to the well-characterized reaction center of purple bacteria, while the reaction center of photosystem 1 (PS1) is related to the green sulfur bacteria, as is convincingly documented here. An operon encoding the P840 reaction center of Chlorobium limicola f.sp. thiosulfatophilum has been cloned and sequenced. It contains two structural genes, coding for proteins of 730 and 232 amino acids. The first protein resembles the large subunits of the PS1 reaction center. Putative binding elements for the primary donor, P840 in Chlorobium and P700 in PS1, and for the acceptors A0, A1, and FeS center X are conserved. The second protein is related to the PS1 subunit carrying the FeS centers A and B. An adjacent third gene, not belonging to the reaction center, encodes a protein related to dolichyl-phosphate-D-mannose synthase from yeast. The different origins of PS1 and PS2 are discussed.

Amino Acid Sequence↗
PubMed1992

Cloning, sequencing, and expression of the Escherichia coli peptide methionine sulfoxide reductase gene.

The gene encoding peptide methionine sulfoxide reductase was cloned from an Escherichia coli genomic library using an oligonucleotide probe based on the amino-terminal sequence of the protein. The nucleotide sequence revealed that the gene codes for a polypeptide of 212 amino acid residues with a calculated molecular weight of 23,314. The protein has been overexpressed in E. coli and is present as a soluble active species.

Amino Acid Sequence↗
PubMed1992

The photosystem I-like P840-reaction center of green S-bacteria is a homodimer.

An operon encoding the P840 reaction center of Chlorobium limicola f.sp.thiosulfatophilum has been cloned and sequenced. It contains two structural genes coding for proteins of 730 and 232 amino acids. The first protein resembles the large subunits of the Photosystem I (PS I) reaction center. Putative binding elements for the primary donor, P840 in Chlorobium and P700 in PS I and for the acceptors A(o), A(1) and FeS-center X are conserved. The second protein is related to the PS I subunit carrying the FeS-centers A and B. Since all our efforts to find a gene for a second, large subunit failed, the P840 reaction center probably is homodimeric.

Amino Acid Sequence↗