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Biomedical subjects

N Horn

Publications and source records attributed to N Horn.

At least 55 records · Page 3Linked to original sources
PubMed1996

Appraisal system for community child health doctors.

An appraisal system for Community Child Health Doctors in Nottingham is described and evaluated. All staff are invited to an annual meeting with their consultant, preparation documents having been filled in by both appraisee and appraiser beforehand. These form the basis of the session, which is predominantly a self-assessment. A written report of the appraisal is produced, with sections on current performance (kept by appraiser and appraise only), training needs, and objectives (copies sent to the academic team and the medical manager). The system was assessed by questionnaires to both appraisers and appraisees. There was general agreement that the system had been adequately explained, and that the preparation documents and the appraisal time were useful. The written report was generally accepted as being a reliable record of the appraisal. Three of the fifteen appraisees were unhappy with the system, feeling it was a negative experience which concentrated on weaknesses. Others made positive comments. It was not always possible to achieve protected time. Some of the reports were delayed. The appraisal system described was found to be acceptable and workable by most people involved. The need for adequate administrative and clerical support was noted.

Attitude of Health Personnel↗
PubMed1996

Molecular analysis of the regulation of nisin immunity.

The genetic determinants controlling immunity to nisin are coordinately regulated, along with biosynthesis genes, in response to an environmental signal, nisin or a nisin analogue. The nisR gene product, the putative response regulator of nisin biosynthesis, was found to be a vital component of this induction mechanism. This protein forms part of a two-component regulatory system which controls the expression of genes involved in nisin immunity and biosynthesis. Analysis of the structural requirements of the external signal, using nisin fragments and engineered nisin variants, indicated that the 12 amino-terminal residues of the molecule are a minimum requirement for induction, with an intact ring A being an essential component. Changes throughout the molecule also affected its induction capacity. The production of certain variant nisins by engineered lactococcal strains is reduced in parallel with the strains' immunity to nisin. This can be attributed to inefficient induction by the variant molecule. Treating growing cultures with nisin restored full immunity and maximized the yields of nisin variants by the producer strains.

Chromosome Mapping↗
PubMed1996

Structure-activity relationships in the peptide antibiotic nisin: role of dehydroalanine 5.

A mutant of the peptide antibiotic nisin in which the dehydroalanine residue at position 5 has been replaced by an alanine has been produced and structurally characterized. It is shown to have activity very similar to that of wild-type nisin in inhibiting growth of Lactococcus lactis and Micrococcus luteus but is very much less active than nisin as an inhibitor of the outgrowth of spores of Bacillus subtilis. These observations, which parallel those of W. Liu and J. N. Hansen (Appl. Environ. Microbiol. 59:648-651, 1993) on the corresponding mutant of the related antibiotic subtilin, are discussed in terms of the mechanism(s) of action of these antibiotics.

Alanine↗
PubMed1996

Menkes disease: recent advances and new insights into copper metabolism.

Copper is a trace element necessary for the normal function of several important enzymes but copper homeostasis is still poorly understood. In recent years remarkable progress has been made in this field following the isolation of the gene defective in Menkes disease. Menkes disease and occipital horn syndrome are X-linked recessive disorders, demonstrating the vital importance of copper, which is also highly toxic in excessive amounts. Its destructive effects are reflected in the autosomal recessive Wilson's disease. Progressive neurodegeneration and connective tissue disturbances are the main manifestations of Menkes disease. Although many patients present a severe clinical course, variable forms can be distinguished, and the occipital horn syndrome has been suggested to be a mild allelic form. The Menkes locus is mapped to Xq13.3 and the gene defective in Menkes disease has been isolated by positional cloning. The gene is predicted to encode an energy-dependent copper-binding protein, the first intracellular copper transporter described in eukaryotes. Isolation of the gene and subsequent characterization of the exon-intron organization now enables the establishment of DNA-based diagnostic methods. Furthermore, identification of the Menkes disease gene led to other important findings, such as isolation of its mouse homologue, confirming the allelic relationship between Menkes disease and occipital horn syndrome, and isolation of the defective genes in Wilson's disease and its rat homologue.

Animals↗
PubMed1995

A cassette vector for protein engineering the lantibiotic nisin.

Expression vectors are described that make use of a plasmid-encoded nisA cassette encoding the peptide component of nisin. Specific mutations can readily be incorporated throughout the coding region of nisA. Using this vector in a nisA mutant host, three variant nisins, with dehydroalanine (Dha) residues changed to Ala residues, were generated.

Alanine↗
PubMed1995

Characterization of the exon structure of the Menkes disease gene using vectorette PCR.

The gene defective in Menkes disease, an X-linked recessive disturbance of copper metabolism, has been isolated and predicted to encode a copper-binding P-type ATPase. We determined the complete exon-intron structure of the Menkes disease gene, which spans about 150 kb of genomic DNA. The gene contains 23 exons, and the ATG start codon is in the second exon. All of the exon-intron boundaries were sequenced and conformed to the GT/AT rule, except for the 5' splice site of intron 9. A preliminary comparison demonstrated a striking similarity between the exon structures of the Menkes and Wilson disease genes, giving insight into their evolution.

Adenosine Triphosphatases↗
PubMed1995

Isolation of nisin-producing Lactococcus lactis strains from dry fermented sausages.

A total of 4608 lactic acid bacteria (LAB) were isolated from 24 Spanish fermented sausages and screened for bacteriocin production. Two strains, BB24 and G18, produced bacteriocins that inhibited a broad spectrum of Gram-positive bacteria. BB24 and G18 were tentatively identified as Lactococcus lactis by carbohydrate fermentation patterns and other biochemical characteristics. The characterization of their bacteriocins suggested that both could be the well-known lantibiotic nisin. This was confirmed by PCR analysis of their genomic DNA. Nucleotide sequencing revealed that they produced nisin A. The fact that BB24 and G18 were isolated from sausages produced in two different regions of Spain suggests that nisin-producing L. lactis strains may be more widespread in meat products than previously thought. Nisin produced by L. lactis BB24 has been purified to homogeneity by a procedure that included ammonium sulphate precipitation and cation-exchange, hydrophobic-interaction and reverse-phase chromatography. The purification procedure was simple, rapid and reproducible.

Bacteriocins↗
PubMed1994

Analysis of Mnk, the murine homologue of the locus for Menkes disease, in normal and mottled (Mo) mice.

Menkes disease (MNK) lies immediately proximal to pphosphoglycerate kinase (PGK1) in Xq13 in human. Phenotypic similarities between MNK patients and murine mottled (Mo) mutants strongly suggest that both defects are caused by mutations at the same locus. Human MNK cDNA clones and a genomic subclone derived from a 40-kb YAC clone that includes Pgk1 have been used to position the murine homologue of Menkes disease (MNK, Mnk) immediately proximal to, and within 150-200 kb of, phosphoglycerate kinase (Pgk1) on the mouse X chromosome using interspecific backcross analysis and pulsed-field gel electrophoresis. A related autosomal locus has been mapped to mouse chromosome 18. RFLVs at Mnk between inbred strains of mice that show a strong association with the presence of the Mo phenotype have been detected. Hybridization of 4.1 kb of the 4.5-kb MNK coding sequence failed to reveal any deletions or alterations to restriction fragments containing exons of the Mnk locus in 9 Mo mutants. Furthermore, no genomic deletions or alterations > 20 kb were detected in 10 independently derived Mo mutants using pulsed-field gel electrophoresis. As no deletions or alterations at the Mnk gene were found, we suggest that any mutations in Mnk that cause the Mo phenotype are likely to be due to small changes at the nucleotide level and/or small deletions (< 20 kb) that lie outside the coding sequence.

Animals↗
PubMed1994

First trimester prenatal diagnosis of Menkes disease by DNA analysis.

Menkes disease is an X linked recessive disorder of copper metabolism characterised by neurological symptoms and connective tissue manifestations. The defective gene in Menkes disease has recently been isolated and the gene product is predicted to be a copper transporting ATPase. The diagnosis of Menkes disease has hitherto been performed by biochemical analysis, based on intracellular accumulation of copper. Cloning the gene opened up the possibility of establishing precise and reliable carrier and prenatal diagnosis by defining the molecular defect. In this report we describe the partial deletion of the Menkes gene in a patient who had inherited the mutation from his phenotypically normal mother. This information enabled us to perform prenatal diagnosis by direct mutation analysis of the mother's sixth pregnancy and we detected the same deletion, indicating that the male fetus was affected. This first prenatal diagnosis of Menkes disease by direct mutation analysis shows some advantages of DNA analysis compared to biochemical diagnosis.

Abortion, Induced↗
PubMed1993

Clinical and biochemical consequences of copper-histidine therapy in Menkes disease.

Menkes disease (MD) is an X-linked recessively inherited neurodegenerative disorder of copper (Cu) metabolism leading to death in early childhood. Symptoms are attributed to deficient activity of Cu-dependent enzymes. Limited experience has been reported concerning clinical and biochemical consequences of parenteral treatment with copper-(histidine)2-complex (Cu-His) in MD. Cu-His was administered in a 13-week-old boy with MD by daily intramuscular injections. After 6 weeks of therapy, Cu and caeruloplasmin in serum and Cu in CSF were normalized. The excessive dopamine level in CSF was corrected after 3 months of treatment. After 6 weeks of Cu supplementation, complete reduction of epileptic discharges, improved muscular tone and increased motor activities were observed. Developmental regression stopped and was replaced by a slight progression. Death at the age of 19 months was caused by septicaemia due to a fulminant urinary tract infection; there was no evidence of chronic Cu toxicity. These findings suggest that Cu-His supplementation may be a promising palliative treatment in MD.

Bone and Bones↗
PubMed1993

Isolation of a candidate gene for Menkes disease that encodes a potential heavy metal binding protein.

Menkes disease is a lethal-X linked recessive disorder associated with copper metabolism disturbance. We have recently mapped two chromosome breakpoints related to this disease in a 1 megabase yeast artificial chromosome contig at Xq13.3. We now report the construction of a phage contig and the isolation of candidate partial cDNAs for the Menkes disease gene. The candidate gene expresses an 8 kb message in all investigated tissues, and deletions were detected in 16% of 100 unrelated Menkes patients. The deduced partial protein sequence shared the GMTCXXC motif with bacterial metal resistance operons, suggesting a potential heavy metal binding protein. These findings should lead to more accurate prenatal diagnosis of this severe disease and a better understanding of the cellular homeostasis of essential heavy metals.

Adenosine Triphosphatases↗
PubMed1993

Insulin-like growth factors (IGF) I and II and IGF binding proteins 1, 2 and 3 during low-dose growth hormone (GH) infusion and sequential euglycemic and hypoglycemic glucose clamps: studies in GH-deficient patients.

To evaluate the short-term effects of growth hormone (GH), insulin and different levels of glycemia on insulin-like growth factors (IGF) I and II and IGF binding proteins (IGFBP) 1, 2 and 3, we studied six GH-deficient adolescents during a night and the following day in the postabsorptive (basal) state followed by sequential euglycemic (5 mmol/l) and hypoglycemic (3 mmol/l) glucose clamps concomitant with an intravenous infusion (starting at 24.00 h) of GH (35 micrograms/h) or saline. Current GH therapy was withdrawn 24 h prior to each study. Nocturnal levels of IGF-I, IGF-II, IGFBP-2 and IGFBP-3 remained stable during both studies. Nocturnal serum IGFBP-1 increased and correlated inversely with insulin in both studies. Regression analysis revealed a significant inverse correlation between mean nocturnal IGFBP-2 and IGFBP-3 levels. During the daytime, serum IGF-I declined slowly during saline infusion, whereas serum IGF-II remained stable in both studies. Serum IGFBP-1 displayed a gradual significant decline during the basal state and the euglycemic and hypoglycemic clamps seemed to be unaffected by GH levels. By contrast, serum IGFBP-2 remained stable during the same period in both the GH and the saline study. Serum IGFBP-3 declined insignificantly during the daytime in the saline study.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Clinical studies of IGFBP-2 by radioimmunoassay.

A specific radioimmunoassay for human IGFBP-2 was developed using a polyclonal antiserum directed against a partial sequence (hIGFBP-2(176-190)). The tracer was prepared by radioiodination of a [Tyr]o-hIGFBP-2(176-190) derivative. The assay was used to study IGFBP-2 levels in numerous clinical and experimental situations. There was little circadian fluctuations of serum level which showed a marked age-dependence with high levels at birth and senescence and low levels during puberty. Decreased IGFBP-2 levels were present in untreated insulin-dependent diabetes mellitus (IDDM), in acromegaly and during dexamethasone suppression test. GH deficiency, fasting, IGF-I administration to patients with GH receptor deficiency, hepatic failure and insulinomas caused a moderate increase of serum IGFBP-2. Markedly elevated levels were found in chronic renal failure, non-islet cell tumour induced hypoglycemia and leukaemias. The fact that all possible relationships between insulin secretion and IGFBP-2 levels could be identified suggests that insulin is not a major regulator. In general, there was an inverse relationship with serum IGFBP-3 (except IDDM) and IGFBP-2 levels were high in situations where free IGF-II should be expected to be high. The tentative conclusion would therefore be that free IGF-II is a major regulator of circulating IGFBP-2.

Animals↗