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Biomedical subjects

J C Walker

Publications and source records attributed to J C Walker.

At least 37 records · Page 2Linked to original sources
PubMed1998

Human responses to propionic acid. I. Quantification of within- and between-participant variation in perception by normosmics and anosmics.

The objective of this study was to fully characterize normosmic perception of stimuli expected to cause widely varying degrees of olfactory and nasal trigeminal stimulation and to directly evaluate the possible role of olfactory nerve stimulation in nasal irritation sensitivity. During each of four identical test sessions, four anosmic and 31 normosmic participants were presented with a range of concentrations extending from peri-threshold for normosmics to supra-threshold for anosmics. For each session, odor (O) and nasal irritation (NI) sensitivities were summarized in terms of the concentrations required to produce four sensation levels ('iso-response' concentrations). Within-participant variation in these iso-response concentrations was < 10-fold for 95% of normosmics, for both O and NI. For O but not NI, these apparent fluctuations in sensitivity were largely accounted for by the uncertainty surrounding the iso-response concentrations calculated for each session. Anosmics exhibited minimal within- and between-participant variation in NI and required, for all but the highest perceptual level, a higher concentration than almost all normosmics. Between-participant variation, expressed in terms of 90% confidence interval widths, was approximately 0.5 log units for both O and NI for the highest perceptual level, but increased to approximately 0.8 and 1.8 log units, respectively, for the lowest (peri-threshold) level. Our findings suggest that: (i) most apparent variation over time in O sensitivity is actually a reflection of the uncertainty surrounding estimates of sensitivity obtained for each session; (ii) within- and between-participant variation in O sensitivity is far less than is commonly reported; and (iii) low to moderate levels of NI in normosmics are the result of relatively weak trigeminal stimulation combined with much greater olfactory activation.

Adolescent↗
PubMed1998

Optic disc swelling in Crohn's disease.

PURPOSE: To provide a review of the causes of optic disc swelling in patients suffering from inflammatory bowel disease. METHODS: Two illustrative cases of bilateral optic disc swelling are presented: one in a patient known to have Crohn's disease and the other in a patient whose investigations revealed the disease. The possible causes of optic disc swelling in inflammatory bowel disease, based on a literature review, are tabulated and discussed with reference to the presented cases. RESULTS/CONCLUSIONS: Optic disc swelling is a rare complication of inflammatory bowel disease. Previously reported cases have been attributed to peripapillary inflammation, optic disc ischaemia or intracranial hypertension. Postulated causes of optic nerve ischaemia include a local vasculitis or general hypercoagulability. The underlying aetiology of intracranial hypertension is often elusive. Older studies suggest a relationship between corticosteroid treatment and/or iron deficiency anaemia, while modern imaging emphasises the need to exclude dural venous sinus thrombosis.

Adult↗
PubMed1997

Electrophoretic analysis of cyanide depletion by Pseudomonas alcaligenes.

Bacterial-facilitated depletion of cyanide is under development for remediation of heap leach operations in the gold mining industry. Capillary electrophoresis was found to be a powerful tool for quantifying cyanide depletion. Changes in cyanide concentration in aqueous suspensions of Pseudomonas alcaligenes bacteria and cyanide at elevated pH were easily monitored by capillary electrophoresis. The resulting data can be used to study rates of cyanide depletion by this strain of bacteria. Concentrations of these bacteria at 10(5) cells/mL were found to reduce cyanide from 100 ppm to less than 8 ppm in four days. In addition, other ions of interest in cyanide metabolism, such as formate, can be simultaneously analyzed. Direct UV detection of cyanide at 192 nm further simplifies the analytical method for these ions.

Culture Media↗
PubMed1997

Comparison of 49 laparoscopic myomectomies with 49 open myomectomies.

STUDY OBJECTIVES: To compare the results of open myomectomy with those of laparoscopic myomectomy, and to assess complications, surgical results, total hospital cost, and morbidity associated with each procedure. DESIGN: Retrospective chart review. SETTING: Private practice of one surgeon, and Department of Obstetrics and Gynecology, Rush Medical College, Chicago, Illinois. PATIENTS: Ninety-eight women with symptomatic uterine leiomyomata. INTERVENTIONS: Forty-nine consecutive laparoscopic myomectomies were performed between 1993 and 1995, and 49 open myomectomies were performed between 1983 and 1995. MEASUREMENTS AND MAIN RESULTS: Indications for both procedures were similar, including menometrorrhagia, pelvic pain, and enlarging myomata. Mean operating time for open myomectomies was 133 minutes versus 264 minutes for laparoscopies (p <0.0001). Mean blood loss was 340 ml and 110 ml, respectively (p <0. 001). The greatest blood loss was 1000 ml in the open group and 800 ml in the laparoscopic group. Uterine size at surgery was 12 to 14 weeks in 42.9% of the open group and 9 to 11 weeks in 51% of the laparoscopy group. The open group incurred a total of 272 hospital days versus 29 days in the laparoscopic group (maximum 25 and 3 days, respectively; mean 5.6 and 0.6 days, respectively; p <0.001). The frequency of postoperative complications was higher in the open group (17) than in the laparoscopic group (5, p = 0.0068). Of patients in whom postoperative adhesions were evaluated, the overall frequency of adhesions was lower in the laparoscopic group. Three women in the open group required postoperative transfusions, compared with none in the laparoscopic group. Seven pregnancies have thus far occurred in the laparoscopic group. Three women delivered at term by elective cesarean section, at which no evidence of uterine dehiscence was found. Estimated average cost of each procedure, expressed in April 1995 dollars using the Consumer Price Index, were $14,461 for open myomectomies and $13,814 for laparoscopies (p = 0.65). Linear regression with residual analysis was performed on costs for both groups and revealed significantly increasing time trend for open myomectomies. During the years of this study, the open procedures increased in price at a rate of $868/year. The cost of laparoscopic myomectomies showed no time trend. CONCLUSIONS: Compared with open myomectomy, laparoscopic myomectomy had lower morbidity, no identifiable trend of increasing hospital cost, minimal hospital stay, and fewer complications.

Adult↗
PubMed1997

Interaction of the maize and Arabidopsis kinase interaction domains with a subset of receptor-like protein kinases: implications for transmembrane signaling in plants.

The kinase interaction (KI) domain of kinase-associated protein phosphatase (KAPP) interacts with the phosphorylated form of an Arabidopsis thaliana receptor-like protein kinase (RLK). The KI domain may recruit KAPP into an RLK-initiated signaling complex. To examine additional roles that this domain may play in plant signal transduction, a search was conducted for other KI domain-containing proteins. One gene was isolated which encodes a KI domain, the maize homolog of KAPP. To test whether the maize KI domain associates with other maize proteins, it was used as a probe in a protein-protein interaction cloning strategy. A new maize RLK, KI domain interacting kinase 1 (KIK1), was identified by its interaction with the maize KI domain. The maize KI domain and the KIK1 kinase domain association required phosphorylation of the kinase. This work establishes that the KI domain phosphorylation-dependent signaling mechanism is present in both monocots and dicots. Additionally, it was determined that both the maize and Arabidopsis KI domains interact with several but not all of the active RLKs assayed. These multiple associations imply that KAPP may function in a number of RLK-initiated signaling pathways.

Amino Acid Sequence↗
PubMed1997

Cloning, sequence, and expression of a blood group B active recombinant alpha-D-galactosidase from pinto bean (Phaseolus vulgaris).

A cDNA encoding pinto bean alpha-D-galactosidase [E.C. 3.2.1.22] was obtained by amplification of cDNA using highly conserved sequences found in eucaryotic alpha-D-galactosidases. Subsequently a full length Phaseolus cDNA clone was obtained that is 1537 nt long and contains untranslated 5' and 3' sequences. The nucleotide sequence of the cDNA has a high degree of homology with other eucaryotic alpha-D-galactosidase genes. The recombinant alpha-D-galactosidase (rGal) was expressed in Escherichia coli and purified by ion exchange and affinity chromatography. Purified rGal was homogeneous by SDS-PAGE and had relative masses of 40.1 and 45.4 kDa under nonreducing and reducing conditions, respectively. The N-terminal sequence of the expressed protein contained the sequence GNGLGQTPPMG corresponding to that deduced from the cDNA sequence. The native molecular weight for rGal was determined to be 32.18 kDa by Sephacryl S-200 chromatography. The specific activity of the rGal was 349 mu moles of PNP-alpha-D-galactopyranoside hydrolyzed per mg of pure rGal per min. rGal was highly specific for alpha-D-galactosyl residues and degraded B oligosaccharide. No detectable hemagglutinin or protease activity was present in the preparations. Furthermore, rGal was active against the blood group B antigen on native human erythrocytes in cell suspension assays. The only detectable RBC phenotypic change was loss of the B and P1 epitopes. Recombinant Phaseolus vulgaris alpha-D-galactosidase may have useful biotechnical applications in the potential mass production of enzymatically converted, universally transfusable type O RBCs. alpha-D-galactosidase [E.C. 3.2.1.22] has been purified from a variety of procaryotic and eucaryotic species. Most alpha-D-galactosidases have similar low molecular weight substrate specificities, but activity against high molecular weight substrates is variable. Terminal alpha-D-galactoside residues are present in glycoproteins and glycolipids. Some alpha-D-galactosidases have activity against alpha-D-galactosyl residues on cell membrane glycoconjugates. Glycosidases with this property are useful for carbohydrate structural studies and biotechnical applications. Enzymes free of other glycosidase activities with activity near neutral pH are particularly useful for membrane modification studies on native cells. Complex sugar chains in glycolipids and glycoproteins have often been implicated in the growth and development of eucaryotes. In particular, complex sugar chains play an important role in the recognition of self in the immune system. Some alpha-D-galactosidases can modify certain carbohydrate membrane epitopes, thereby modulating the immune response. For example, the blood group B epitope expressed on erythrocytes contains a terminal alpha-D-galactosyl residue. Individuals lacking this antigen produce naturally occurring complement fixing antibodies to the B epitope. Hydrolysis of this terminal saccharide destroys the antigenic activity of the B determinant producing H antigen (blood type O) on erythrocytes. Only rare individuals produce clinically significant antibodies to the H antigen, and therefore, type O red blood cells are "universally" compatible and in great demand. Dhar purified alpha-D-galactosidase isozymes from Phaseolus vulgaris and characterized their activity. To our knowledge, our laboratory, in a brief report, is the first to describe the cloning of the gene and the use of recombinant enzyme for seroconverting blood type B to O cells. This paper describes the cloning, sequence, expression, purification, and characterization of recombinant alpha-D-galactosidase. Activity of the recombinant enzyme on the native human erythrocyte blood group B epitope is shown.

ABO Blood-Group System↗
PubMed1997

Cloning and characterisation of the aroA and aroD genes of Shigella dysenteriae type 1.

The aroA and aroD genes from Shigella dysenteriae type 1, encoding 5-enolpyruvylshikimate 3-phosphate synthase and 3-dehydroquinase, respectively, were cloned by polymerase chain reaction (PCR). Their nucleotide sequences were determined and predicted to code for 46 kDa and 27.5 kDa proteins, respectively. Protein expressed from these genes using the minicell system, corresponded to the size of the predicted protein products. The cloned genes were shown to be functional by complementation of Escherichia coli aroA- and aroD- mutants. The predicted amino acid sequences of the cloned aroA (427 amino acids) and aroD (252 amino acids) genes of S. dysenteriae type 1 were found to be highly homologous to the corresponding genes in other bacterial species, indicating the high conservation of these housekeeping genes. The use of the cloned aroA and aroD genes in the development of a vaccine strain against S. dysenteriae is discussed.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed1997

A blast of gas in the latest Paleocene: simulating first-order effects of massive dissociation of oceanic methane hydrate.

Carbonate and organic matter deposited during the latest Paleocene thermal maximum is characterized by a remarkable -2.5% excursion in delta 13C that occurred over approximately 10(4) yr and returned to near initial values in an exponential pattern over approximately 2 x 10(5) yr. It has been hypothesized that this excursion signifies transfer of 1.4 to 2.8 x 10(18) g of CH4 from oceanic hydrates to the combined ocean-atmosphere inorganic carbon reservoir. A scenario with 1.12 x 10(18) g of CH4 is numerically simulated here within the framework of the present-day global carbon cycle to test the plausibility of the hypothesis. We find that (1) the delta 13C of the deep ocean, shallow ocean, and atmosphere decreases by -2.3% over 10(4) yr and returns to initial values in an exponential pattern over approximately 2 x 10(5) yr; (2) the depth of the lysocline shoals by up to 400 m over 10(4) yr, and this rise is most pronounced in one ocean region; and (3) global surface temperature increases by approximately 2 degrees C over 10(4) yr and returns to initial values over approximately 2 x 10(6) yr. The first effect is quantitatively consistent with the geologic record; the latter two effects are qualitatively consistent with observations. Thus, significant CH4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum. This conclusion is of broad interest because the flux of CH4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present-day anthropogenic CH4 sources.

Atmosphere↗
PubMed1997

Formulary management in a military treatment facility.

In an environment of increased fiscal responsibility and cost constraints, the medical staff must take an active role in deciding how an institution's operating budget is spent. A major expense of a military treatment facility (MTF) is maintaining an adequate and cost-effective formulary. The large number of pharmaceuticals available on the market forces a decision regarding which products to stock. Decision analysis is a technique that helps a medical staff to manage its formulary by listing all of the objective and subjective considerations. The Department of Defense Pharmacoeconomic Center has developed a tri-service formulary to standardize a basic drug list that would be available in each military treatment facility. However, this list cannot be expected to answer all of the factors a medical staff must weigh in developing an MTF-specific formulary. Many considerations must be addressed in these decisions, including the beneficiary population, the potential diagnoses as defined by a database such as the Retrospective Case Mix Analysis System or the Military Health Services System, the institution's mission and defined scope of care, physician interests and specialization, and facility limitations. Military treatment facilities can maintain an appropriate stock of medications that is specific for the scope and practice of a medical staff and work within a budget through careful planning and employment of a decision matrix. This balance of appropriateness and fiscal responsibility allows the maximum range of services within a facility.

Decision Support Techniques↗
PubMed1996

Cloning, expression and characterization of a blood group B active recombinant alpha-D-galactosidase from soybean (Glycine max).

A cDNA encoding soybean alpha-D-galactosidase [E.C. 3.2.1.22] was obtained by screening a soybean library with Phaseolus alpha-D-galactosidase cDNA. The Glycine max alpha-D-galactosidase cDNA is 1.75 kb long and contains untranslated 5' and 3' sequences. The deduced amino acid sequence of the soybean gene has a high degree of homology with other eucaryotic alpha-D-galactosidases. Recombinant alpha-D-galactosidase (rGal) was expressed in Pichia pastoris and purified by affinity chromatography. Purified rGal was homogeneous as judged by SDS-PAGE analysis with the relative molecular mass under reducing conditions of 39.8, and under nonreducing conditions 38.0 kDa. The expressed protein contained the sequence NGLGHTPPMG at the N-terminus, corresponding to the deduced amino acid sequence of the soybean gene. The relative native molecular mass by Sephacryl S-200 chromatography was determined to be 33.1 kDa. The specific activity was 295.6 mumoles of PNP-alpha-D-galactopyranoside hydrolyzed per mg pure rGal per min. rGal was highly specific for alpha-D-galactosyl residues. No detectable hemagglutinin or protease activity was present in the preparations. Furthermore, rGal was active against the blood group B antigen in native human erythrocyte cell suspension assays. The only detectable erythrocyte phenotypic change was loss of the B and P1 epitopes. Consequently, recombinant Glycine max alpha-D-galactosidase may have useful biotechnical applications in the potential mass production of universally transfusable type O erythrocytes by enzymatic conversion.

ABO Blood-Group System↗
PubMed1996

Plant transmembrane receptors: new pieces in the signaling puzzle.

The past few years have seen the mechanisms used by plants to transmit extracellular signals into the cytoplasm begin to be uncovered. Multiple plant proteins have been identified that resemble the receptor protein kinases of animal cells. These are known as receptor-like protein kinases or RLKs. Variations in structure and patterns of synthesis of different RLKs suggest that these proteins are involved in mediating a variety of cellular signaling processes, can respond to diverse extracellular signals and have different physiological functions.

Arabidopsis Proteins↗
PubMed1995

Time course of reinnervation of the olfactory bulb after transection of the primary olfactory nerve in the pigeon.

Horseradish peroxidase (HRP) histochemistry was used to study the time course of reinnervation of the pigeon olfactory bulb after simple transection of the primary olfactory nerve. At selected intervals (9, 13, 29, 61 and 93 days) after transection of the right olfactory nerve, a concentrated solution of HRP was instilled in both nasal cavities. Intracarotid perfusion was performed 3 days after nasal instillation of HRP and 40-microns sections of olfactory bulb processed with the tetramethylbenzidine (TMB)-HRP histochemical protocol to visualize olfactory receptor axon terminals reinnervating the glomerular layer of the bulb. The total area of reinnervation of four representative regions in the bulb of the transected side were compared with that on the control bulb. The area of innervation by newly reconstituted olfactory axons was approximately 17% of control values at the 12-day posttransection time interval. A progressive increase in the area of reinnervation was observed over time. Reinnervation of the right bulb was approximately 70% complete at the 32-day posttransection time interval and indistinguishable from the left control bulb at the 64- and 96-day posttransection time intervals. A uniform pattern of reinnervation of different bulb regions was observed at all time intervals. These results indicate that the peripheral olfactory system of the pigeon is capable of complete reconstitution after nerve transection. Our findings should be useful in guiding functional comparisons of normal and newly reconstituted peripheral olfactory systems in the pigeon.

Animals↗
PubMed1995

Possible role of oceanic heat transport in early Eocene climate.

Increased oceanic heat transport has often been cited as a means of maintaining warm high-latitude surface temperatures in many intervals of the geologic past, including the early Eocene. Although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically, determining how additional oceanic heat transport would take place has yet to be accomplished. That the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked. Using early Eocene climate as an example, we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early Eocene conditions. Our interpolation of early Eocene paleotemperature data indicate that an approximately 30% increase in poleward heat transport would be required to maintain Eocene high-latitude temperatures. This increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early Eocene rates. Either oceanic processes were very different from those of the present to produce the early Eocene climate conditions or oceanic heat transport was not the primary cause of that climate. We believe that atmospheric processes, with contributions from other factors, such as clouds, were the most likely primary cause of early Eocene climate.

Atmosphere↗
PubMed1995

Influence of variable rates of neritic carbonate deposition on atmospheric carbon dioxide and pelagic sediments.

Short-term imbalances in the global cycle of shallow water calcium carbonate deposition and dissolution may be responsible for much of the observed Pleistocene change in atmospheric carbon dioxide content. However, any proposed changes in the alkalinity balance of the ocean must be reconciled with the sedimentary record of deep-sea carbonates. The possible magnitude of the effect of shallow water carbonate deposition on the dissolution of pelagic carbonate can be tested using numerical simulations of the global carbon cycle. Boundary conditions can be defined by using extant shallow water carbonate accumulation data and pelagic carbonate deposition/dissolution data. On timescales of thousands of years carbonate deposition versus dissolution is rarely out of equilibrium by more than 1.5 x 10(13) mole yr-1. Results indicate that the carbonate chemistry of the ocean is rarely at equilibrium on timescales less than 10 ka. This disequilibrium is probably due to sea level-induced changes in shallow water calcium carbonate deposition/dissolution, an interpretation that does not conflict with pelagic sedimentary data from the central Pacific.

Atmosphere↗