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Biomedical subjects

D M Roberts

Publications and source records attributed to D M Roberts.

At least 73 records · Page 4Linked to original sources
PubMed1987

Microdistribution of immature African blackflies resulting from water velocity and turbulence preferences.

1. The velocity preferences of larval and pupal blackflies were studied experimentally by comparing the colonization of plastic strings placed in different velocity ranges; and also by investigating the simuliid microdistribution under natural conditions in the river. This required a novel method described for taking spot measurements of water velocity. 2. Simulium mcmahoni de Meillon, S. hirsutum Pomeroy and S. cervicornutum Pomeroy were most abundant in slow velocities (0.3-1.0 m s-1), S. colasbelcouri Grenier & Ovazza and S. hargreavesi Gibbins preferred 1.1-1.8 m s-1, S. squamosum Enderlein and S. vorax Pomeroy 1.9-2.2 m s-1. 3. The larvae of S. hargreavesi and S. cervicornutum preferred a higher velocity range compared with their pupae. 4. In moderate velocities (1.1-1.4 m s-1), the abundance of S. hargreavesi was greater under turbulent conditions than in smooth-flowing water, but this was reversed at very high velocities (2.3-2.6 m s-1). 5. Velocity had no apparent effect on substrate preference when substrates of different flexibilities were compared for three blackfly species. All avoided the most flexible substrates and preferred ones consisting of rigid articulating plates. Anisopteran predators were found to have a similar substrate choice.

Analysis of Variance↗
PubMed1987

Identification of environmental Vibrio vulnificus isolates with a DNA probe for the cytotoxin-hemolysin gene.

We screened 44 lactose-positive Vibrio strains isolated from the marine environment for homology with a 3.2-kilobase DNA fragment encoding the Vibrio vulnificus cytotoxin-hemolysin gene. All 29 marine isolates identified as V. vulnificus on the basis of numerical taxonomy and DNA-DNA hybridization studies hybridized with the cytotoxin gene probe, as did all V. vulnificus reference strains. Homologous gene sequences were identified in no other lactose-positive marine vibrio isolates nor in 10 other Vibrio species.

Animals↗
PubMed1987

An inexpensive apparatus for automatic continuous dehydration.

An apparatus is described for automatic dehydration of material using the principle of continuous dilution. Specimens may be dehydrated, in a period chosen by the operator, for as little as 30 min to as much as 16 hr (overnight). The apparatus is inexpensive both to construct and to run.

Histological Techniques↗
PubMed1987

Nigerian blood-fed blackflies (Diptera. Simuliidae) caught in flight: relative activity and host preferences.

Using a vehicle-mounted net, over 1000 blood-fed blackflies were collected in flight, showing that they had a much higher level of activity during this stage than was previously expected, particularly in Simulium squamosum. Activity was greatest in blood-fed females with Stage IV eggs, presumably because they were starting to search for oviposition sites. S. squamosum, S. adersi and S. vorax showed a moderate level of activity in flies with Stage II and III eggs, although these are normally considered to be resting stages. Blood-fed flies with Stage I eggs were relatively rare. Analysis of 601 blood meals showed that S. hargreavesi, S. squamosum and S. vorax were primarily cattle-feeders, although a few S. squamosum had fed on man (showing that this species has a high level of zoophily in this area). The few S. adersi, S. hirsutum and S. nigritarse collected had fed mainly on birds.

Animals↗
PubMed1986

Trimethyllysine and protein function. Effect of methylation and mutagenesis of lysine 115 of calmodulin on NAD kinase activation.

Unmethylated calmodulins have been enzymatically methylated at lysine 115, and a direct effect of this methylation on NAD kinase activation has been shown. Similar to naturally occurring calmodulins with trimethyllysine 115, the enzymatically methylated calmodulins activated an NAD kinase preparation to a maximal level that was at least 3-fold lower than the level of activation obtained with the corresponding unmethylated calmodulins. Methylation did not alter the cyclic nucleotide phosphodiesterase activator properties of these calmodulins. A genetically engineered calmodulin containing an arginine at position 115 instead of a lysine was produced by site-specific mutagenesis of a cloned synthetic calmodulin gene. The arginine derivative retained the higher maximal NAD kinase activator properties of the unmethylated calmodulins but was no longer susceptible to the effects of the methyltransferase. The data indicate that the reduction in the level of NAD kinase activation is the direct result of trimethylation of lysine 115 of calmodulin, provide a precedent for a functional effect of trimethyllysine in a protein, and raise the possibility that some of calmodulin's physiological activities may be affected by lysine methylation.

Amino Acid Sequence↗
PubMed1985

Chemical synthesis and expression of a calmodulin gene designed for site-specific mutagenesis.

A gene coding for a calmodulin was synthesized and expressed in Escherichia coli. The gene was produced by the enzymatic ligation of 61 chemically synthesized DNA fragments. The gene possesses 27 unique, regularly spaced, restriction endonuclease cleavage sites to facilitate gene mutagenesis by the replacement of specific gene segments with synthetic double-stranded DNA. An expression vector containing the calmodulin gene was used to transform E. coli. Purification and characterization of calmodulin (VU-1 calmodulin) expressed by these transformants showed that it lacks two posttranslational modifications: an amino-terminal blocking group and N epsilon, N epsilon, N epsilon-trimethyllysine at position 115. The cyclic nucleotide phosphodiesterase activator properties of VU-1, higher plant, and vertebrate calmodulins were not statistically different. However, VU-1 calmodulin was found to activate nicotinamide adenine dinucleotide (NAD) kinase to a maximal level that was at least 3-fold higher than that found with higher plant and vertebrate calmodulins. This higher level of activation is also characteristic of calmodulins from Dictyostelium discoideum and Chlamydomonas reinhardtii [Roberts, D. M., Burgess, W. H., & Watterson, D. M. (1984) Plant Physiol. 75, 796-798; Marshak, D. R., Clarke, M., Roberts, D. M., & Watterson, D. M. (1984) Biochemistry 23, 2891-2899]. The only common feature among Dictyostelium, Chlamydomonas, and VU-1 calmodulins not found in higher plant and vertebrate calmodulins is an unmethylated lysine at position 115. The results indicate that the lack of methylation of lysine-115 may contribute to the maximal level of NAD kinase activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Lung function, atopy, specific hypersensitivity, and smoking of workers in the enzyme detergent industry over 11 years.

A study of 2800 workers employed in three factories of the two major manufacturers of enzymatic products in the United Kingdom covering 11 years of operation from 1969 to 1980 showed that 2344 workers had sufficient lung function data to meet the operational criteria and these were analysed in three separate groups by factory locations. Spirometry and prick tests for specific skin reactions to standardised enzyme were performed at six monthly intervals for the first six years of the study and then annually. Factory enzyme dust and total dust measurements were made to determine the degree of dust exposure of the subjects. The lung function of the factory groups was analysed for the effects of working in the detergent industry, the degree of exposure to enzymes, skin prick test positivity to enzymes, atopicity, and smoking. The 4.5% of workers who had experienced respiratory effects from enzymes were analysed separately. Exposure to the enzyme allergen has had no significant long term effect on the lung function of the detergent workers. A higher proportion of atopics than non-atopics became skin test positive to the allergen and more smokers than non-smokers were sensitised. The overall lung function of detergent workers showed 39 ml/year loss in FEV1 on the 11 year longitudinal study and 51 ml/year loss on the lateral (cross sectional) analysis with better lung function in the south east than the north west of England. In the development of the methodology for the study several potential problems were discovered that could remain unrecognised in a cross sectional analysis performed in isolation.

Adult↗
PubMed1985

Vertical distribution of flying black-flies (Diptera: Simuliidae) in Central Nigeria.

Flying black-flies were collected using an array of 4 nets mounted on a vehicle at heights between 0.15 and 3.0 m above the ground. The vertical distribution differed amongst the 8 most abundant species, but within a particular species such as S. squamosum, there was no significant difference in the vertical distribution of the males and females, nor between females of different physiological conditions. This infers that the height of the trap on the vehicle will not normally be a source of bias during population studies. However, there was some evidence of circadian changes in the vertical distribution; during the afternoon, black-flies of all species flew higher compared with in the evening.

Animals↗
PubMed1984

Structural and functional properties of calmodulin from the eukaryotic microorganism Dictyostelium discoideum.

Calmodulin was purified from the eukaryotic microorganism Dictyostelium discoideum and characterized in terms of its nearly complete primary structure and quantitative activator activity. The strategy for amino acid sequence analysis took advantage of the highly conserved structure of calmodulin and employed a new procedure for limited cleavage of calmodulin that uses a protease from mouse submaxillary gland. Fourteen amino acid sequence differences between Dictyostelium and bovine calmodulin were identified unequivocally, as well as an unmethylated lysine at residue 115 instead of N epsilon, N epsilon, N epsilon-trimethyllysine. Seven of the amino acid substitutions in Dictyostelium calmodulin are novel in that the residues at these positions are invariant in all calmodulin sequences previously examined, most notably an additional residue at the carboxy terminus. Comparison of the Dictyostelium calmodulin sequence with other calmodulin sequences shows that the region with the greatest extended sequence identity includes parts of the first and second structural domains and the interdomain region between domains 1 and 2. Dictyostelium calmodulin activated bovine brain cyclic nucleotide phosphodiesterase in a manner indistinguishable from that of bovine brain calmodulin. However, Dictyostelium calmodulin activated pea NAD kinase to a maximal level 4.6-fold greater than that produced by bovine brain calmodulin. This functional difference demonstrates the potential biological importance of the limited number of amino acid sequence differences between Dictyostelium calmodulin and other calmodulins and provides further insight into the structure, function, and evolution of the calmodulin family of proteins.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1984

Comparison of the NAD Kinase and Myosin Light Chain Kinase Activator Properties of Vertebrate, Higher Plant, and Algal Calmodulins.

In the preceding paper (Lukas, Iverson, Schleicher, Watterson 1984 Plant Physiol 75: 788-795), we reported that the amino acid sequence of spinach calmodulin has at least 13 amino acid sequence differences from vertebrate calmodulin. In the present study, we investigated the effect of these amino acid sequence substitutions on the enzyme activator properties of vertebrate and plant calmodulins. Calmodulins from spinach and the green alga Chlamydomonas reinhardtii activate chicken gizzard myosin light chain kinase in a manner similar but not identical to chicken calmodulin. In contrast, these calmodulins have very different NAD kinase activator properties. The concentration required for half-maximal activation of pea seedling NAD kinase by spinach calmodulin (3-4 nanomolar) is lower than the corresponding concentrations of chicken (20 nanomolar) and Chlamydomonas (40 nanomolar) calmodulins. However, the maximum level of activation obtained with Chlamydomonas calmodulin is 4- to 6-fold higher than spinach or chicken calmodulin. These data indicate that the limited structural heterogeneity among calmodulins have differential effects on their biochemical activities.

Journal Article↗
PubMed1984

Development and Distribution of a Lectin from the Stems and Leaves of Dolichos biflorus.

The stems and leaves of the Dolichos biflorus plant contain a lectin that cross-reacts with antiserum against the seed lectin. This cross-reactive material (CRM) was followed during early seedling growth, stem elongation, and seed development using a specific radioimmunoassay.No CRM was detected in developing seeds, but very low levels were found in dormant and imbibed seeds. As germination proceeds, the CRM accumulates at the apex of both etiolated and green seedlings in the epicotyl and leaves. Lower amounts of CRM are found in the cotyledons and hypocotyl, but no CRM was detected in the roots.The amount of CRM in the first and second stem internodes increases during elongation and gradually declines after the completion of elongation. Approximately 80% of the CRM in the stems of 19-day-old Dolichos biflorus plants is associated with the elongating tissues. These results are discussed with respect to the possible roles of lectins in plants.

Journal Article↗
PubMed1983

Analysis of suborganellar fractions from spinach and pea chloroplasts for calmodulin-binding proteins.

Purified chloroplasts from spinach and pea leaves were subfractionated into envelope, thylakoid, and stroma fractions and were analyzed for calmodulin-binding proteins using a 125I-calmodulin gel overlay assay. Calmodulin binding was primarily associated with a major polypeptide (Mr 33,000) in the envelope membrane fraction. In contrast, major calmodulin-binding proteins were not detected in the thylakoid or stroma fractions. Our results provide the first evidence of calmodulin-binding proteins in the chloroplast envelope, and raise the possibility that calmodulin may contribute to the regulation of chloroplast function through its interaction with calmodulin-binding proteins in the chloroplast envelope. In addition, our results combined with those of other investigators support the proposal that subcellular organelles may be a primary site of calmodulin action.

Calmodulin-Binding Proteins↗