Biomedical subjects

B Pontoppidan

Publications and source records attributed to B Pontoppidan.

13 recordsLinked to original sources

PubMed2001

Purification and characterization of myrosinase from the cabbage aphid (Brevicoryne brassicae), a brassica herbivore.

Aphids are among the most serious insect pests of agricultural crops in the world. They often have specific hosts, and the cabbage aphid (Brevicoryne brassicae) is a specialist on Cruciferae. It has previously been described that certain insects contain the enzyme myrosinase (EC 3.2.3.1), which is considered an important defence enzyme of crucifers. Myrosinase was purified to homogeneity from cabbage aphid soluble extracts using anion-exchange and phenyl-Sepharose chromatography. The protein has an apparent subunit molecular mass of 57-58 kDa and is a dimer. The isoelectric point is 4.9 and the enzyme has a temperature optimum around 40 degrees C. The enzyme was active towards the glucosinolates tested, sinigrin and glucotropaeolin, but was inhibited by ascorbate at concentrations that normally activate plant myrosinases. Using sinigrin as the substrate Km was determined as 0.41 mM, and the kcat as 36 s(-1). With glucotropaeolin the Km and kcat values were determined as 0.52 mM and 22.8 s(-1), respectively. The enzyme was stable upon storage at 4 degrees C for many months, but lost some activity upon freezing. The insect myrosinase did not cross-react with antibodies raised to plant myrosinase. Peptide sequencing of a tryptic digest of the protein showed homology to beta-glucosidases. The presence of myrosinase in an insect pest specialist may be an example of a coevolution process that facilitates host specialization.

Amino Acid Sequence↗

PubMed2000

Myrosinase: gene family evolution and herbivore defense in Brassicaceae.

Glucosinolates are a category of secondary products present primarily in species of the order Capparales. When tissue is damaged, for example by herbivory, glucosinolates are degraded in a reaction catalyzed by thioglucosidases, denoted myrosinases, also present in these species. Thereby, toxic compounds such as nitriles, isothiocyanates, epithionitriles and thiocyanates are released. The glucosinolate-myrosinase system is generally believed to be part of the plant's defense against insects, and possibly also against pathogens. In this review, the evolution of the system and its impact on the interaction between plants and insects are discussed. Further, data suggesting additional functions in the defense against pathogens and in sulfur metabolism are reviewed.

Amino Acid Sequence↗

PubMed1996

Bladder management and urinary tract infections in Danish hospitals, nursing homes, and home care: a national prevalence study.

OBJECTIVE: To establish the prevalence of urinary tract infection in patients undergoing various forms of bladder management. DESIGN: A nationwide descriptive point-prevalence survey with logistic regression analysis of the data relating infection to bladder management. SETTING: Fifteen hospitals, 21 nursing homes, and 13 home care districts throughout Denmark. PATIENTS: Information was collected on 3,665 patients. On the day of the study, 349 patients had indwelling catheters and 1,150 were using external urine drainage systems (condoms or diapers) for bladder management. RESULTS: The prevalence of urinary tract infections in catheterized patients and those using external drainage systems was 13.2% and 8.1%, respectively. The prevalence of hospital-acquired urinary tract infection (4.2%) had not changed from that reported in 1978. The proportion of these infections related to the indwelling catheter, however, had reduced from 66% to 30%. Logistic regression analysis confirmed that, when corrected for the patient-related confounders (female gender, age > 60 years, incontinence, immobility, and stay in hospital for longer than 15 days), condoms (odds ratio [OR], 5.94; 95% confidence interval [CI95], 2.8 to 12.5), indwelling catheters (OR, 3.3; CI95, 2.3 to 4.8), and diapers (OR, 1.5; CI95, 1.1 to 2.1) were significantly (P < .001, P < .001, and P = .008, respectively) related to infection. CONCLUSIONS: Prevalence surveys have revealed that over the period 1978 to 1991, during which efforts have been made to restrict the use of indwelling catheters and to encourage the care of catheterized patients according to guidelines recommended by the Danish National Centre for Hospital Hygiene, the percentage of hospital-acquired urinary tract infections associated with indwelling catheters has been halved. External urine drainage systems, however, have emerged as significant risk factors for urinary tract infection.

Aged↗

PubMed1995

Nucleotides of tRNA (Glu) involved in recognition by barley chloroplast glutamyl-tRNA synthetase and glutamyl-tRNA reductase.

The biosynthesis of delta-aminolevulinate (ALA), via the C-5 pathway, requires tRNA(Glu) as a cofactor for the glutamyl tRNA(Glu) synthetase and the glutamyl tRNA(Glu) reductase which are the first two enzymes in this three step pathway. These two enzymes form a ternary complex with the tRNA(Glu) in Chlamydomonas reinhardtii suggesting that the recognition elements on the tRNA cofactor are different for each enzyme. Chemical modification and comparative studies with tRNA(Glu)s from a number of species were used to determine the nucleotides involved in the recognition of the barley chloroplast tRNA(Glu) by the barley enzymes. The barley chloroplast tRNA(Glu) is chemically modified both before and after ligation to glutamate with monobromobimane or CNBr. The chemically modified tRNA(Glu) is a poor substrate for the glutamyl-tRNA synthetase and the chemically modified glutamyl-tRNA(Glu) is used as a substrate for glutamyl-tRNA(Glu) reductase. The tRNA(Glu) from the chloroplasts if barley, Chlamydomonas reinhardtii, tobacco, cucumber, wheat and spinach and tRNA(Glu) from Synechocystis PCC6803, Escherichia coli, barley germ and bakers yeast and the barley chloroplast tRNA(Gln) are all effective substrates for the barley chloroplast glutamyl-tRNA synthetase. A comparison of the sequences of these tRNAs shows 19 conserved bases and five of these bases, G10, A26, U34, U35 and A37 are suggested as recognition elements of barley glutamyl tRNA(Glu) synthetase by assuming a similar binding orientation as in the crystal structure of the E. coli tRNA(Gln) GlnRS complex. The glutamyl-tRNA(Glu) from E. coli, bakers yeast and barley germ and the barley chloroplast glutamyl-tRNA(Gln) are not effective substrates for the barley chloroplast glutamyl-tRNA(Glu) reductase. A comparison of the sequences of these four tRNA species with the sequences of the tRNA(Glu) species that can be used as substrate by the glutamyl-tRNA(Glu) reductase yields seven common differences in the primary sequence. These 7 nucleotides, A7-U66, U29-A41, A53-U61, and U72 are expected to be required for recognition by the barley chloroplast glutamyl-tRNA(Glu) reductase.

Aldehyde Oxidoreductases↗

PubMed1995

The management of urinary catheters: compliance of practice in Danish hospitals, nursing homes and home care to national guidelines.

The compliance of practice to national guidelines on urethral catheter care has been examined. Questionnaires on the practices used with patients under their care were sent to 1350 nursing staff. Replies were received from 1153 individuals, 692 from hospitals, 345 from nursing homes and 116 from home care. While national guidelines stress the importance of maintaining a closed urine drainage system, the results revealed that 25.4% of respondents opened the drainage system to collect samples of urine for analysis, 57.9% to perform bladder washouts and 76% to change urine bags. 26% of respondents reported that they collected urine samples for routine bacteriological surveillance, a procedure considered unnecessary in the guidelines. 83% of staff reported that they washed their hands after emptying urine bags. Staff awareness of written guidelines for various aspects of catheter care ranged from 25-68% in hospitals, 27-45% in nursing homes and 7-17% in home care. A marginal costs analysis was performed to estimate the economic consequences of non-compliance to the national guidelines.

Anti-Bacterial Agents↗

PubMed1994

Purification and partial characterisation of barley glutamyl-tRNA(Glu) reductase, the enzyme that directs glutamate to chlorophyll biosynthesis.

5-Aminolevulinic acid for chlorophyll synthesis in greening barley is formed from glutamate. One of the steps involved in the conversion of glutamate to 5-aminolevulinic acid involves a reduction of glutamyl-tRNA(Glu) to glutamate 1-semialdehyde and tRNA(Glu). An enzyme catalysing this reduction was purified from the stroma of greening barley chloroplasts. An approximately 270-kDa protein composed of 54-kDa identical subunits was identified as the barley glutamyl-tRNA(Glu) reductase after purification by Sephacryl S-300, Cibacron Blue-Sepharose, 2'-5'-ADP-Sepharose, Mono S, Mini Q and Superose 12 chromatography. The sequence of 18 amino acids from the N-terminus of the reductase is 50% identical to a cDNA-deduced domain of the Arabidopsis thaliana hemA protein and encoded in a barley hemA cDNA sequence. This is an unequivocal demonstration that the glutamyl-tRNA(Glu) reductase subunit of higher plants is encoded in a hemA gene of the nuclear genome. Heme at 4 microM concentration or glutamate 1-semialdehyde at 200 microM caused a 50% inhibition of the reductase activity. Micromolar concentrations of Zn2+, Cu2+ and Cd2+ also inhibited barley glutamyl-tRNA(Glu) reductase.

Aldehyde Oxidoreductases↗

PubMed1994

Enzymic and mechanistic studies on the conversion of glutamate to 5-aminolaevulinate.

Higher plants, algae, cyanobacteria and several other photosynthetic and non-photosynthetic bacteria synthesize 5-aminolaevulinate by a tRNA(Glu)-mediated pathway. Glutamate is activated at the alpha-carboxyl by ligation to tRNA(Glu) with an aminoacyl-tRNA synthetase. An NADPH-dependent reductase converts glutamyl-tRNA(Glu) to glutamate 1-semialdehyde, which is finally converted to 5-aminolaevulinate by an aminotransferase. These components are soluble and in plants and algae are located in the chloroplast stroma. In plants and algae the tRNA(Glu) is encoded in chloroplast DNA whereas the enzymes are encoded in nuclear DNA. The tRNA(Glu) has a hypermodified 5-methylaminomethyl-2-thiouridine-pseudouridine-C anticodon and probably plays a role in the light-dark regulation of 5-aminolaevulinate synthesis. Ligation of glutamate to tRNA(Glu) requires ATP and Mg2+ and proceeds via a ternary intermediate. Glutamyl-tRNA(Glu) reduction appears to involve formation of a complex. Glutamate 1-semialdehyde non-enzymically synthesized by reductive ozonolysis from gamma-vinyl GABA is used as substrate by the last enzyme. Glutamate-1-semialdehyde aminotransferase contains pyridoxal phosphate as a prosthetic group. The enzyme is converted to spectrally different forms by treatment with 4,5-diaminovalerate or 4,5-dioxovalerate. The pyridoxamine 5'-phosphate form of the enzyme converts (S)-glutamate 1-semialdehyde to 5-aminolaevulinate via 4,5-diaminovalerate through a bi-bi ping-pong mechanism.

Aminolevulinic Acid↗

PubMed1993

Management of urinary bladder function in Danish hospitals, nursing homes and home care.

The purpose of this study was to determine the prevalence of the various devices used for bladder function management in Denmark and to assess the scope for the use of alternatives to the indwelling urethral catheter. Data were collected on 1581 hospital patients, 1341 nursing home residents and 743 patients receiving home care. The sample populations were characterized by age, sex and independence in the activities of daily living. The prevalence of indwelling catheters in the three groups of patients was 13.2%, 4.9% and 3.9%, respectively. The equivalent figures for condom drainage systems were 1.5%, 0.8% and 1.2%, and for napkins 10.1%, 52.1% and 34.1%. Comparison of the results from this survey with earlier data indicates that over the period 1980-1991 (during which efforts have been made in Denmark to restrict indwelling bladder catheterization and encourage the use of alternative devices) there has been a reduction in the prevalence of indwelling catheters in hospital medical wards from 13.7% to 6.6%. Examination of the reasons for catheterization revealed that the proportions of patients catheterized because of incontinence were 14% in hospitals, 31% in nursing homes and 33% in home care. There is clearly a need to continue the educational efforts to inform staff of the infection risks and complications associated with indwelling catheters and persuade them of the advantages of the alternative techniques for care of the incontinent patient.

Activities of Daily Living↗

PubMed1992