PubMed Health⌕ Search

Biomedical subjects

M T Walsh

Publications and source records attributed to M T Walsh.

At least 37 records · Page 2Linked to original sources
PubMed1993

Potassium and anaesthesia.

Potassium is the principle intracellular ion, and its concentration and gradients greatly influence the electrical activity of excitable membranes. Because anaesthesia is so intimately involved with electrically active cells, potassium concentrations in surgical patients have received considerable attention in diagnostic and therapeutic applications. With the ongoing evolution in the indications for potassium, it is important to review the role of potassium in cellular activity, in storage and regulation, in diseases that alter potassium homeostasis, and in the therapeutic implications of perioperative alterations of potassium concentration. A rational approach to abnormal potassium values and the use of potassium in the operating room is sought, based on a physiological understanding of risks and benefits.

Anesthesia↗
PubMed1993

Isolation of St. Louis encephalitis virus from a killer whale.

We report the isolation of St. Louis Encephalitis (SLE) virus from a mature male killer whale (Orcinus orca). This represents the first isolation of SLE virus from a marine mammal. The animal presented with reduced appetite, rapidly became lethargic and subsequently died. Virus-induced CPE was observed in a dolphin cell line, SP-1K (ATCC CCL 78), inoculated with brain, kidney, and lung tissues obtained at necropsy. Electron microscopy of infected SP-1K cells revealed the presence of virions having morphology and size resembling members of the Flaviviridae. Final identification as SLE virus was made by neutralization and immunofluorescence staining tests.

Journal Article↗
PubMed1992

Structure of the N- and O-glycans of the A-chain of human plasma alpha 2HS-glycoprotein as deduced from the chemical compositions of the derivatives prepared by stepwise degradation with exoglycosidases.

The structure of the glycans of the A-chain of human plasma alpha 2HS-glycoprotein was established from the chemical compositions of its derivatives prepared by sequential enzymatic degradation of the carbohydrate moiety, from the determination of the kind and amount of the monosaccharides liberated after each step of the enzymatic digestion, and from the distinct specificity of the highly purified exoglycosidases. The exoglycosidases were three sialidases (Vibrio cholerae, fowl plague virus, and Arthrobacter ureafaciens), two beta-galactosidases (Streptococcus pneumoniae and bovine testis), one alpha-N-acetylgalactosaminidase, one beta-N-acetylglucosaminidase, and one alpha-mannosidase. Utilizing sialidases with different cleavage specificities, the number of alpha 2-3- and alpha 2-6-linked sialic acid residues could be separately determined. As to the beta-galactosidases, the enzyme isolated from S. pneumoniae cleaves only beta 1-4-linked galactose residues, whereas the bovine testes enzyme acts on both the beta 1-4- and beta 1-3-linked galactose residues. Jack bean beta-N-acetylglucosaminidase cleaves beta 1-2, beta 1-4, and beta 1-6 GlcNAc with higher activity for the beta 1-2. Jack bean alpha-mannosidase cleaves alpha 1-2, alpha 1-6, and alpha 1-3 Man with greater activity for alpha 1-2 and alpha 1-6. Bovine liver alpha-N-acetylgalactosaminidase cleaves O-linked GalNAc. On the basis of these results, the A-chain of alpha 2 HS-glycoprotein was found to possess two biantennary N-glycans and two O-linked trisaccharides.

Blood Proteins↗
PubMed1992

An insight into domain structures and thermal stability of gamma-crystallins.

The thermal behavior of gamma II, gamma IIIA, gamma IIIB, and gamma IVA crystallin, from calorimetric and spectral studies, has been analyzed in terms of selective unfolding of domains, interdomain interactions, conformational stability, and the existence of intermediates in the order-disorder transition equilibrium. The major endothermic transition (Tm) observed calorimetrically for all four fractions occurs between 67 and 78 degrees C, with enthalpy change (delta H) from 80 to 150 kcal/mol, values that agree reasonably well with those from spectroscopic measurements. gamma II and gamma IIIB show a second thermal event at T less than Tm whereas gamma IIIA and gamma IVA showed no additional transition. Urea-induced equilibrium unfolding of gamma II at acidic pH, unlike gamma IVA, is biphasic as monitored by CD and fluorescence, indicating the existence of an intermediate. The absence of a cooperative transition in gamma IVA in acidic urea and the appearance of a single endotherm in differential scanning calorimetry at low pH have been attributed to a structured intermediate that melts at low temperature. The difference in the folding/unfolding of gamma II and gamma IVA has been explained by subtle differences in the packing arrangement of their two domains and interactions between them. Thermal aggregation of gamma-crystallins could be prevented either by preincubation with ionic detergents or at low pH or in the presence of chemical denaturant, indicating that the protein surface charge and solvent polarity influence their stability. An increase in the 8-anilino-1-naphthalenesulfonate-bound fluorescence during heat denaturation also suggests that the thermal aggregation is governed by hydrophobic interactions.

Anilino Naphthalenesulfonates↗
PubMed1992

Amino acid sequence of human plasma galactoglycoprotein: identity with the extracellular region of CD43 (sialophorin).

The amino acid sequence of galactoglycoprotein purified from human plasma was elucidated to 75% completeness by using chemical degradation of peptides and glycopeptides derived from digests of the protein with seven specific proteases. This sequence represents a polypeptide chain of approximately 220 amino acid residues including a high content of serine, threonine, alanine, and proline with one N-linked and multiple O-linked glycans. Comparison of peptide sequences from the native galactoglycoprotein and the deglycosylated derivative demonstrated the locations of 25 sites of O-glycosylation and three serine sites that are not glycosylated. The homogeneous N terminus was established as serine. C-terminal analysis revealed multiple C-terminal residues, suggesting that galactoglycoprotein molecules are of varying lengths. A search of a protein data base revealed that the galactoglycoprotein polypeptide is identical to the N-terminal (extracellular) polypeptide region of the blood-cell surface molecule CD43 (sialophorin, leukosialin). Further support of the relatedness of these molecules was obtained by immunoprecipitation of 125I-labeled galactoglycoprotein by monoclonal anti-CD43 antibodies. The composition and properties of the molecules together with the known structure of the gene encoding CD43 suggest that galactoprotein is derived by proteolytic cleavage from transmembrane "hexasaccharide CD43," known to be expressed on neutrophils, activated T lymphocytes, and platelets.

Amino Acid Sequence↗
PubMed1991

Micellar subunit assembly in a three-layer model of oligomeric alpha-crystallin.

Differential scanning calorimetry was performed to monitor the heat-induced changes that occur in the structural domain of lens alpha-crystallin. Circular dichroism and fluorescence also were used to resolve the controversial issue of the quaternary structure of alpha-crystallin. Based on the thermal behavior as monitored by these techniques, a model is proposed that can account for all previous data as well as the currently reported thermal data. The proposed model of native alpha-crystallin has a three-layer structure in which the inner layer (core) is a micelle containing 12 subunits arranged in cuboctahedral symmetry. The apolar region is directed inward constituting a hydrophobic core similar to a micelle and adding structural stability. A second layer of six subunits has a similar but not identical structure to the first layer, directing its apolar face toward the hydrophobic core. Thus, these two layers constitute a micelle-like structure with octahedral symmetry. The third layer adds more subunits for a total of not more than 24. Differential scanning calorimetry, circular dichroism, and fluorescence studies indicated that the inner two-layer structure of molecular mass 360 kDa is highly stable and is most likely of the alpha m form. The three-layer structure of the native protein, however, is rather unstable. At 35-45 degrees C the outer layer dissociates from the inner two layers, and at higher temperatures rapidly reassociates to a slightly modified two-layer structure with a stability similar to that of alpha m. The proposed model does not require any specific assembly of the alpha A and alpha B subunits in each layer, but the fluorescence results suggest that the native inner two layers probably contain mostly alpha A.

Animals↗
PubMed1991

Expression, secretion, and lipid-binding characterization of the N-terminal 17% of apolipoprotein B.

The N-terminal 17% of human apolipoprotein B (apoB-17) was expressed in murine C127 cells following transfection with a bovine papilloma virus-based expression vector. A permanent cell line overexpressing the expected 89-kDa protein was selected and characterized. Pulse-chase experiments showed that the depletion of intracellular apoB-17 follows an apparent first-order kinetics with t1/2 = 51 min. Under conditions of continuous labeling, greater than 60% of the total synthesized apoB-17 was secreted in a soluble form, approximately 98% lipid-poor and approximately 2% lipid-bound. Inclusion of 1.2 mM oleate resulted in 5- and 2.5-fold increases in the amount of labeled apoB-17 in the p less than 1.063 g/ml and 1.063 less than p less than 1.21 g/ml fractions, respectively, which was coordinated with increased secretion of radiolabeled core lipids, triacylglycerols, and cholesteryl esters. Thus under conditions in which lipid pools are enriched a greater fraction of apoB-17 may be secreted on lipoprotein-like particles. The lipid-poor apoB-17 present in p greater than 1.21 g/ml readily associates with exogenously added dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles to form discoidal particles. Discs formed with DMPC/apoB-17, 7:1 (wt/wt), are 239 +/- 43 A in diameter and 61 +/- 4 A thick and contain approximately 2 molecules of apoB-17 and 2250 molecules of DMPC per disc. Based on volume calculations we conclude that apoB-17 forms an annulus about one bilayer high and 10 A thick surrounding the DMPC disc. Circular dichroic spectra of apoB-17 on DMPC discs showed apoB-17 to contain 39% alpha-helix, 36% beta-sheet, 9% beta-turn, and 16% random coil. To be consistent with this model greater than 70% of apoB-17 on DMPC discs must bind to lipid. These data suggest that the N-terminal 17% of apoB-100 can bind lipid and may contribute to some extent to the stabilization of triglyceride-rich lipoproteins.

Amino Acid Sequence↗
PubMed1991

The effect of the carbohydrate moiety upon the size and conformation of human plasma galactoglycoprotein as judged by electron microscopy and circular dichroism. Structural studies of a glycoprotein after stepwise enzymic carbohydrate removal.

Galactoglycoprotein is a unique human plasma protein [76% carbohydrate (23% N-acetylneuraminic acid, 20% galactose, 3% mannose, 1% fucose and 29% N-acetylgalactosamine plus N-acetylglucosamine) and 24% polypeptide, a single polypeptide chain of about 200 amino acid residues that is high in serine and threonine content] [Schmid, Mao, Kimura, Hayashi & Binette (1980) J. Biol. Chem. 255, 3221-3226]. Highly purified exoglycosidases with well-defined specificities were used to prepare five derivatives of galactoglycoprotein in which sequential residues of N-acetylneuraminic acid, galactose, N-acetylglucosamine, a second galactose and N-acetylgalactosamine were removed with 83% of the total carbohydrate cleaved. C.d. shows that native galactoglycoprotein and all derivatives in aqueous buffer are predominantly random coil, suggesting that removal of a large number of electrostatic net charges, as well as the major portion of the carbohydrate moiety, does not alter the secondary structure of the polypeptide chain. Examination of the size and conformation of tungsten-shadowed galactoglycoprotein and asialo and agalacto derivatives by electron microscopy shows the size and conformation of all three preparations to be similar, with only minor differences in particle length and width.

Antigens, CD↗
PubMed1991

A review of false negative mammography in a symptomatic population.

A review of the mammograms of 871 patients with breast cancer from a symptomatic clinic performed at the General Hospital, Birmingham between 1980 and 1988 revealed an overall false negative rate of 8.6%. There has been a steady fall in the number of cancers missed per year from the commencement of review, and this reduction has been more consistent with improvements in radiographic equipment and technique, particularly the introduction of a radiographic grid. In half of the cases the tumour was missed because no radiological abnormality was detectable, even on reviewing the films, and this rate has remained remarkably stable over the study period, emphasizing the importance of a clinical examination in symptomatic women. Comparison of the histological diagnoses revealed similar percentages of ductal carcinomas, 89.6% in the true positive group compared with 85% in the false negative group. Of the false negative carcinomas, 5.5% were medullary tumours compared to 0.8% in the true positive group.

Adult↗
PubMed1990

Effect of the carbohydrate moiety on the secondary structure of beta 2-glycoprotein. I. Implications for the biosynthesis and folding of glycoproteins.

By use of six highly purified exoglycosidases with well-defined specificity, the oligosaccharide units of human plasma beta 2-glycoprotein I (beta 2I) were modified by sequential enzymatic degradation. The released monosaccharides (NeuAc, Gal, GlcNAc, and Man) were quantified, and the carbohydrate compositions of the resulting glycoprotein (gp) derivatives were determined. The gp was found to be both partially sialylated and galactosylated. These findings which are in agreement with earlier reports suggest that the carbohydrate moiety of beta 2I possesses more bi- than tri-antennas, probably three of the former and two of the latter carbohydrate units. Circular dichroic (CD) spectra of native beta 2I and its derivatives were measured in aqueous buffer and 2-chloroethanol (2-CE). Analysis of these spectra for elements of secondary structure showed beta 2I and most of the derivatives to contain predominantly beta-sheet and beta-turn structures. The lack of alpha-helical structures in aqueous buffer was noted. Removal of a large portion of the carbohydrate moiety did not alter the CD spectra or secondary structure of beta 2I in either aqueous buffer or in 2-CE. However, after enzymatic removal of approximately 96% of the carbohydrate moiety, large significant changes in the spectra and secondary structures were observed. In aqueous buffer a shift in the wavelength minimum occurred, accompanied by an increase in the magnitude of the molar ellipticity and the amount of beta-turn, with a reduction in random coil. One-third of the amino acids which were originally in random coil conformation assumed beta-turns after removal of 96% of the carbohydrate moiety.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate Sequence↗
PubMed1990

Calorimetric and spectroscopic investigation of the unfolding of human apolipoprotein B.

The unfolding of human apolipoprotein B-100 in its native lipid environment, low density lipoprotein (LDL), and in a soluble, lipid-free complex with sodium deoxycholate (NaDC) has been examined using differential scanning calorimetry (DSC) and near UV circular dichroic (CD) spectroscopy. High resolution DSC shows that LDL undergoes three thermal transitions. The first is reversible and corresponds to the order-disorder transition of the core-located cholesteryl esters (CE) (Tm = 31.1 degrees C, delta H = 0.75 cal/g CE). The second, previously unreported, is reversible with heating up to 65 degrees C (Tm = 57.1 degrees C, delta H = 0.20 cal/g apoB) and coincides with a reversible change in the tertiary structure of apoB as shown by near UV-CD. No alteration in the secondary structure of apoB is observed over this temperature range. The third transition is irreversible (Tm = 73.5 degrees C, delta H = 0.99 cal/g apoB) and coincides with disruption of the LDL particle and denaturation of apoB. The ratio of delta H/delta HvH for the reversible protein-related transition suggests that this is a two-state event that correlates with a change in the overall tertiary structure of the entire apoB molecule. The second protein-related transition is complex and coincides with irreversible denaturation. ApoB solubilized in NaDC undergoes three thermal transitions. The first two are reversible (Tm = 49.7 degrees C, delta H = 1.13 cal/g apoB; Tm = 56.4 degrees C, delta H = 2.55 cal/g apoB, respectively) and coincide with alterations in both secondary and tertiary structure of apoB. The changes in secondary structure reflect an increase in random coil conformation with a concomitant decrease in beta-structure, while the change in tertiary structure suggests that the conformation of the disulfide bonds is altered. The third transition is irreversible (Tm = 66.6 degrees C, delta H = 0.54 cal/g apoB) and coincides with complete denaturation of apoB and disruption of the NaDC micelle. The ratio of delta H/delta HvH for the two reversible transitions indicates that each of these transitions is complex which may suggest that several regions or domains of apoB are involved in each thermal event.

Apolipoproteins B↗
PubMed1989

Fatty acid interactions with rat intestinal and liver fatty acid-binding proteins expressed in Escherichia coli. A comparative 13C NMR study.

Enterocytes in the small intestinal mucosa contain abundant quantities of two homologous cytosolic proteins known as intestinal and liver fatty acid-binding proteins (I- and L-FABP, respectively). To elucidate structure-function relationships for these proteins, the interactions between 13C-enriched palmitate and oleate and Escherichia coli-expressed rat I- and L-FABP were systematically compared using 13C NMR spectroscopy. NMR spectra of samples containing fatty acids (FA) and I-FABP at different molar ratios (all at pH 7.2 and 37 degrees C) exhibited a single carboxyl resonance corresponding to FA bound to I-FABP (181.4 ppm, peak I) and an additional carboxyl resonance corresponding to unbound FA in a bilayer phase (179.6 ppm). Peak I reached a maximum intensity corresponding to 1 mol of bound FA/mol of I-FABP under all sample conditions examined. NMR spectra for samples containing FA and L-FABP also exhibited a single carboxyl resonance corresponding to FA bound to L-FABP but at a different chemical shift value (182.2 ppm, peak L). Its maximum intensity varied depending on the physical state of the unbound FA (liquid crystalline or crystalline), the FA used (palmitate or oleate), and the sample pH. In the presence of a liquid crystalline (bilayer) phase, up to 1 (oleate) or 2 (palmitate) mol of FA were bound/mol of L-FABP, but in the presence of a crystalline phase (1:1 acid-soap), up to 3 mol of palmitate were bound/mol of L-FABP (all at pH 7.2). Peak I exhibited little or no ionization shift over a wide pH range (pH 3.0-11.0), and its chemical shift was unaffected by the ionization of Lys and His residues. Hence, the carboxylate group of FA bound to I-FABP was solvent inaccessible and most likely involved in an ion-pair electrostatic interaction with the delta-guanidinium moiety of an Arg residue. In contrast, peak L exhibited an ionization shift and an estimated apparent pKa value similar to that obtained for monomeric FA in water, suggesting that the carboxylate groups of FA bound to L-FABP were solvent accessible and located at or near the protein solvent interface. With decreasing pH, FA dissociated from L-FABP but not I-FABP, as monitored by NMR peak intensities. Concurrently, a large decrease in circular dichroism molar ellipticity was observed with L-FABP but not I-FABP. In conclusion, I-FABP and L-FABP are distinct with regards to their FA-binding stoichiometries, binding mechanisms, and sensitivity to pH.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Secondary structural analysis of retrovirus integrase: characterization by circular dichroism and empirical prediction methods.

The retrovirus integrase (IN) protein is essential for integration of viral DNA into host DNA. The secondary structure of the purified IN protein from avian myeloblastosis virus was investigated by both circular dichroism (CD) spectroscopy and five empirical prediction methods. The secondary structures determined from the resolving of CD spectra through a least-squares curve fitting procedure were compared with those predicted from four statistical methods, e.g., the Chou-Fasman, Garnier-Osguthorpe-Robson, Nishikawa-Ooi, and a JOINT scheme which combined all three of these methods, plus a pure a priori one, the Ptitsyn-Finkelstein method. Among all of the methods used, the Nishikawa-Ooi prediction gave the closest match in the composition of secondary structure to the CD result, although the other methods each correctly predicted one or more secondary structural group. Most of the alpha-helix and beta-sheet states predicted by the Ptitsyn-Finkelstein method were in accord with the Nishikawa-Ooi method. Secondary structural predictions by the Nishikawa-Ooi method were extended further to include IN proteins from four phylogenetic distinct retroviruses. The structural relationships between the four most conserved amino acid blocks of these IN proteins were compared using sequence homology and secondary structure predictions.

Amino Acid Sequence↗
PubMed1989

Are multiple examinations of the gall-bladder helpful?

The pattern of use of the oral cholecystogram and ultrasonocholecystography in the investigation of 1014 patients prior to cholecystectomy was analysed. Three hundred and sixty-eight (36.3%) of our patients had both an oral cholecystogram and an ultrasound examination of the gallbladder. In 193 (52.4%) of these the initial investigation was positive: the second test in this group was rarely helpful and sometimes confusing. Overall the predictive value of a positive first study was 98.5%. We conclude that the use of further investigation following an initially positive result is not justified. By these criteria 18.5% of patients had an unnecessary second investigation.

Adolescent↗
PubMed1988

Interactions of oleic acid with liver fatty acid binding protein: a carbon-13 NMR study.

13C NMR spectroscopy was used to probe the structural interactions between carboxyl-13C-enriched oleic acid (18:1) and rat liver fatty acid binding protein (FABP) and the partitioning of 18:1 between FABP and unilamellar phosphatidylcholine (PC) vesicles. Spectra of systems containing 2-8 mol of 18:1/mol of FABP (but no PC) exhibited one carboxyl resonance (182.2 ppm) corresponding to FABP-bound 18:1. At pH values less than 8.0, an additional carboxyl resonance, corresponding to unbound 18:1 in a lamellar phase, was observed. Both resonances exhibited ionization shifts with estimated apparent pKa values of less than 5 (bound 18:1) and greater than 7 (unbound 18:1). The intensity of the resonance corresponding to FABP-bound 18:1 increased with increasing 18:1/FABP mole ratio and at 8/1 mole ratio indicated that at least 2 and 6 mol of 18:1/mol of FABP were FABP-bound at pH 7.4 and 8.6, respectively. NMR spectra of systems containing equal concentrations (w/v) of FABP and PC and from 1 to 4 mol of total fatty acid (FA)/mol of FABP exhibited two 18:1 carboxyl resonances (182.2 and 178.5 ppm, pH 7.4). The downfield resonance corresponded to FABP-bound 18:1 and the upfield resonance to PC vesicle bound 18:1. At 1/1 mole ratio (FA/FABP), the intensities of both resonances were approximately equal, but at 4/1 mole ratio the resonance for PC vesicle bound 18:1 was 3-fold more intense than that for FABP-bound 18:1. The following conclusions are reached: (i) The carboxyl groups of 18:1 bound to liver FABP experience only one type of binding environment (the aqueous milieu adjacent to the protein surface).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Secondary and tertiary structure of apolipoproteins.

The advent of these and other high-powered techniques for the detailed study of apoLP organization will allow us to obtain a high resolution picture of apoLP conformation both in solution and on native lipoprotein particles.

Apolipoproteins↗
PubMed1987

Urogenital sinus calculi in a sand tiger shark (Odontaspis taurus).

Two calculi were found in the urogenital sinus of a 70 kg female sand tiger shark (Odontaspis taurus). The calculi were white in color, rough surfaced, and spherical in shape. Crystallographic examination revealed that they were composed of magnesium ammonium phosphate hexahydrate (80% struvite) and calcium phosphate (15% carbonate apatite). Approximately 5% of the stone matrix consisted of blood and protein and a distinct bacterial nidus was not present microscopically.

Animals↗