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Biomedical subjects

R G Murray

Publications and source records attributed to R G Murray.

At least 127 records · Page 7Linked to original sources
PubMed1978

Cell envelope associations of Aquaspirillum serpens flagella.

Specific regions of the cell envelope associated with the flagellar basal complex of the gram-negative bacterium Aquaspirillum (Spirillum) serpens were identified by studying each of the envelope layers: outer membrane, mucopeptide, and plasma membrane. The outer membrane around the flagella insertion site was differentiated by concentric membrane rings and central perforations surrounded by a closely set collar. The perforations in both the outer membrane and the isolated mucopeptide layer were of a size accomodating the central rod of the basal complex but smaller than either the L or the P disks. The P disk of the complex may lie between the mucopeptide and the outer membrane. Electron microscopy of intact, spheroplasted, or autolyzed preparations did not adequately resolve the location of the inner pair of disks of the basal complex. Freeze-etching, however, revealed differentiation within the plasma membrane that appeared to be related to the basal complex. The convex fracture face showed depressions which are interpreted as impressions of a disk surrounded by a set of evenly spaced macromolecular studs and containing a central "plug" interpreted as the central rod. In thin sections, blebs, which appear to be associated with the flagellar apparatus, were seen on the cytoplasmic side of the plasma membrane. Superimposing the dimensions of the flagellar basal complex and the spacings of the cell envelope layers and using the position of the L disk within the outer membrane for reference, showed that the S disk might be within and the M disk beneath the plasma membrane. A tentative model was developed for comparison with that based on the structure of the Escherichia coli basal complex.

Bacteriolysis↗
PubMed1978

The envelope of Micrococcus radiodurans: isolation, purification, and preliminary analysis of the wall layers.

Two methods are presented that separate the complex envelope of Micrococcus radiodurans, strain Sark, into its constituent layers. The first involved treating whole cells with 0.025 M Tris buffer (pH 7.5) containing 2 mM of calcium and 3 mM of magnesium, resulting in the degradation of an intermediate ('compartmentalized') layer and consequent sloughing of the outer subunit and interior layers to form vesicles. This treatment also appears to show that the interior layer may be connected with the peptidoglycan-containing 'holey' layer. The second method involves treating whole cells with benzene followed by sonication; the results suggested that this treatment only released the outer layers from the 'compartmentalized' layer and did not degrade layers. Following benzene treatment, digestion of the 'compartmentalized' layer with cold sodium dodecyl sulfate (SDS) released the 'holey' layer. Electrophoretic analysis of some of the isolated layer preparations suggested that the subunit layer consisted of three major proteins of 90 000, 92 000, and 94 000 molecular weight, one minor protein of 100 000, a small amount of carbohydrate associated with the 94 000 protein, and a small amount of a 55 000 lipoprotein. The interior layer contained at least 10 proteins and may be attached to the peptidoglycan-containing 'holey' layer by means of the 55 000 lipoprotein.

Cell Fractionation↗
PubMed1978

Cleavage planes in the envelope of Aquaspirillum bengal.

The cell surface of Aquaspirillum bengal was devoid of superficial wall structure. When cells were freeze-cleaved and etched, multiple fracture planes through the cell envelope were exposed, which was unusual for an aquaspirillum. These included both convex and concave surfaces and they are compared with those of other gram-negative bacteria.

Cell Wall↗
PubMed1978

Role of cardiac output in the pressor responses to graded muscle ischemia in man.

Ten men repeatedly performed leg exercise (100-150 W) for 7 min with 30-min recovery periods interspersed. Both legs were made ischemic by total occlusion (OCCL), first for 3 min immediately after exercise and second for 30 s before exercise ended and 3 min into recovery. In addition legs were occluded for 3 min at rest (seated). OCCL at rest increased mean arterial pressure (MAP) by 9 Torr but did not affect cardiac output (CO) or heart rate (HR). OCCL at the end of exercise significantly raised MAP and HR above control values during 3-min recovery but CO was unaffected. OCCL 30 s before the end of exercise further increased MAP and HR significantly during recovery; MAP, CO, and HR were significantly increased above control values (CO by 2.1 1-min-1) during the 3rd min of recovery. We conclude that a strong reflex from ischemic legs maintains normal or elevated CO during leg OCCL. Thus CO was too high relative to total vascular conductance so that MAP was elevated.

Blood Pressure↗
PubMed1977

Membrane-associated components of the bacterial flagellar apparatus.

At the position of insertion of the flagellum into the Gram-negative bacterial cell envelope, a specialized membrane differentiation has been observed by electron microscopy. This structure, termed concentric membrane rings, is harboured on the under-side of the outer membrane of Spirillum serpens, and forms a plate-like array of up to seven rings (diameter 90 nm) and an interior supporting collar. The concentric membrane rings are sensitive to proteolytic digestion, but are lysozyme and phospholipase resistant. The structures are disrupted by ionic detergents, yet resistant to the action of non-ionic detergents. A model integrating the basal organelle of the bacterial flagellum and the outer membrane of the cell wall is presented.

Bacterial Physiological Phenomena↗
PubMed1977

Purification of a monocytosis-producing activity from Listeria monocytogenes.

The monocytosis-producing activity (MPA) from Listeria monocytogenes is shown to be associated with the cell envelope. Both MPA and immunosuppressive activity were readily extracted with aqueous solvents and separated as two independent activities by gel filtration and ion-exchange chromatography. As little as 10 microng of the resulting MPA-containing fraction caused a ninefold elevation in the level of circulating monocytes. The molecular weight of the fraction was approximately 22,000, and it contained phosphorus and carbohydrate.

Carbohydrates↗
PubMed1976

The renal handling of insulin and thyroid hormones in normal man.

1. The renal extraction of insulin and thyroid hormones T3 and T4 was studied in man by right renal vein catheterization. 2. The mean renal extraction of insulin was 0-46, suggesting that the right renal vein should be utilized in comparable studies. 3. No renal extraction of thyroid hormones was detected.

Adult↗
PubMed1976

Ultrastructural study of polymyxin-resistant isolates of Pseudomonas aeruginosa.

Upon exposure to 6,000 U of polymyxin B sulfate per ml, cells of the polymyxin-sensitive PAO 1 strain of Pseudomonas aeruginosa displayed in thin sections long projections arising from the outer membrane of the cell wall and extensive cytoplasmic degradation with accumulation of cytoplasmic membrane infoldings. Polymyxin-resistant isolates derived from the PAO 1 strain, however, grew well in the presence of 6,000 U of polymyxin per ml and exhibited none of these effects, having instead the appearance of a typically healthy cell. Freeze-etching of cells of the sensitive strain grown in basal medium without polymyxin revealed a concave cell wall layer studded with numerous particles. Freeze-etching of cells of the resistant isolates grown in basal medium containing 6,000 U of polymyxin per ml revealed a concave cell wall layer (i.e., the outer half of the outer membrane) in which most of these particles were absent. Thus, acquisition of resistance to polymyxin was correlated with an alteration in the architecture of the outer membrane. When the resistant isolates were grown in the basal medium lacking polymyxin and then freeze-etched, the particle distribution in the concave cell wall layer resembled that of the sensitive parent strain. The cells had regained sensitivity to polymyxin upon suspension in medium containing 6,000 U/ml as determined by their failure to grow and by internal damages seen in thin sections. These cells also had acquired increased sensitivity to ethylenediaminetetraacetate, whereas the polymyxin-resistant cells grown in the presence of polymyxin were resistant to lysis by ethylenediaminetetraacetate. The polymyxin-resistant isolates were not stable mutants but instead represented an adaptive response to the presence of polymyxin in the medium.

Cell Membrane↗
PubMed1976

Substructure and in vitro assembly of the outer, structured layer of Spirillum serpens.

Electron micrographs of disintegrating units of the outer, structured (HP) layer of Spirillum serpens and of the isolated protein obtained from the HP layer revealed V- and Y-shaped and linear profiles. Interpretation of these forms, influenced by the seemingly trimeric form of the isolated protein and by biochemical data, suggested that the protein subunits were identical and Y shaped. A model is proposed for the assembly of the Y-shaped subunits to form a hexagon composed of two triads (three Y-shaped subunits each). The isolated protein adsorbed to a template of wall fragments (basal layer) to the same degree (over 90%) in high concentrations of Na+, K+ (5 X 10(-2) M), Ca2+, Sr2+, and Mg2+ (10(-2) M). At a lower concentration (4 x 10(-5) M) of the cations there was differential adsorption of the protein. Adsorption to the template in the presence of each cation, followed by dilution, also led to differential release of the protein. The adsorption of the protein to the basal layer was correlated with reassembly of the HP layer on the template. The mechanisms seem to be: (i) an ionic strength-dependent reassembly, which results in an HP layer loosely attached to the template (this layer is easily dissociated by decreasing the ionic strength); and (ii) a cation-specific (Ca2+ or Sr2+, but not Mg2+, Na+, or K+) mechanism independent of ionic strength. In this latter case, the specific cations presumably form strong noncovalent "salt" linkages between triads and the basal layer, enabling stable hexagons and the HP layer to be formed.

Adsorption↗
PubMed1976

Uptake and retention of metals by cell walls of Bacillus subtilis.

Isolated walls of Bacillus subtilis Marburg, prepared in a manner which avoided metal contamination other than by the growth medium, were incubated in dilute metal solutions, separated by membrane filtration (0.22 mum), and monitored by atomic absorption to give uptake data for 18 metals. Substantial amounts of Mg2+, Fe3+, Cu2+, Na+, and K+ (amounts which were often visible as Au3+, and Ni2+ (the higher atomic-numbered elements also visible as electron scattering), and small amounts of Hg2+, Sr2+, Pb2+, and Ag+ were taken into the wall. Some (Li+, Ba2+, Co2+, and Al3+) were not absorbed. Most metals which had atomic numbers greater than 11 and which could be detected by electron microscopy appeared to diffusely stain thin sections of the wall. Magnesium, on the other hand, partitioned into the central region, and these sections of walls resisted ruthenium red staining, which was not true for the other metals. Areas of the walls also acted as nucleation sites for the growth of microscopic elemental gold crystals when incubated in solutions of auric chloride. Retention or displacement of the metals was estimated by a "chromatographic" method using the walls cross-linked by the carbodiimide reaction to adipic hydrazide agarose beads (which did not take up metal but reduced the metal binding capacity of the walls by ca. 1%) packed in a column. When a series of 12 metal solutions was passed through the column, it became evident that Mg2+, Ca2+, Fe3+, and Ni2+ were strongly bound to the walls and could be detected by both atomic absorption and by their electron-scattering power in thin sections, qhereas the other metals were fisplaced or replaced. Partial lysozyme digestion of the walls (causing a 28% loss of a [3H]diaminopimelic acid label) greatly diminished the Mg2+ retention but not that of Ca2+, Fe3+, or Ni2+, indicating that there are select sites for various cations.

Bacillus subtilis↗
PubMed1976

Comparison of 12-lead and computer-analysed 3 orthogonal lead electocardiogram in coronary artery disease.

The computer-analysed 3 orthogonal lead system ("3-lead ECG") provides a rapid and consistent interpretation of the electrocardiogram. In 102 patients undergoing selective coronary arteriography, the ability of such a system to predict the presence of absence of coronary artery disease and the site of myocardial ischaemia was compared with that of the conventional scalar electrocardiogram interpreted by cardiologists ("12-lead ECG"). Each system predicted the site of myocardial ischaemia with equal accuracy. The 3-lead ECG was a more sensitive index (3-lead ECG sensitivity=77%; 12-lead ECG sensitivity=70%) but less specific (3-lead ECG specificity=74%; 12-lead ECG specificity=78%). In coronary artery disease, the predictive "index of merit" for the 3-lead ECG was 0-51, compared with 0-48 for the 12-lead ECG. These results provide further justification for the routine use of the 3 orthogonal lead electrocardiogram.

Adult↗
PubMed1976

Dependence of the superficial layers of Spirillum putridiconchylium on Ca2+ or Sr2+.

Chelating agents disrupted the superficial layers on Spirillum putridiconchylium and adsorption of cationized ferritin indicated that both upper and lower surfaces of superficial layer fragments, as well as the outer membrane surface, possessed areas which were negatively charged. Growth of the bacterium in 1% casamino acids (vitamin free) resulted in cells which were devoid of the superficial layers, and negative staining of these cells revealed in amorphous precipitate together with a vesicular outer membrane component extruding from their surfaces into the medium. Addition of either 1 mM Ca2+ or 1 mM Sr2+ to the growth medium produced the typical regularly structured cell surface, whereas addition of equal concentrations of Li+, Na+, K+, Mg2+, Ba2+, Mn2+, Fe3+, or three polyamines produced the structureless surface.

Adsorption↗
PubMed1975

Demonstration of cell division by septation in a variety of gram-negative rods.

Through use of an initial fixative employing a combination of crotonaldehyde and glutaraldehyde, septa were preserved in thin sections of dividing cells of strains of Pseudomonas aeruginosa, Salmonella typhimurium, Shigella sonnei, and Escherichia coli when grown at 30 C in a dilute basal medium. The same procedures, however, revealed only a constrictive division process in Proteus vulgaris and Erwinia sp. This adds to the evidence that septation, although difficult to demonstrate, is the process of cell division in the enteric gram-negative rods and the pseudomonads and that constriction is a fixation artifact in these organisms.

Aldehydes↗
PubMed1975

Analysis of the cell wall and lipopolysaccharide of Spirillum serpens.

Isolated walls of Spirillum serpens VHA contained lipid, lipopolysaccharide, and protein in amounts similar to those of other gram-negative organisms. The loosely bound lipids consisted mainly of phosphatidylethanolamine, lyso-phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol. Lipopolysaccharide was tightly bound to the wall and could only be removed in a substantial amount after digestion of the wall with Pronase. The lipopolysaccharide contained L-glycero-D-mannoheptose, rhamnose, glucosamine, ethanolamine, and phosphate in common with many of the lipopolysaccharides isolated from the Enterobacteriaceae. However, 2-keto-3-deoxyoctonic acid was not detected. Several unidentified sugars were present. The fatty acid composition resembled that found in lipopolysaccharides isolated from various pseudomonads. Two major regions were identified in the polysaccharide moiety, one apparently corresponding to the core polysaccharide and the other corresponding to the side-chain polysaccharide as in enterobacterial and pseudomonad lipopolysaccharides. The side chains were obtained as low-molecular-weight material and their structure was partially elucidated by the isolation and partial characterization of N-acetylglucosaminyl-(1 leads to 4)-rhamnose.

Bacterial Proteins↗
PubMed1975

Surface arrays on the cell wall of Spirillum metamorphum.

A complex and easily disrupted arrangement of macromolecules was present on the outer (lipopolysaccharide) membrane of the cell wall of Spirillum metamorphum. Separation of the arrays from the cell and spontaneous reassembly into regularly structured complexes usually occurred during preparation for electron microscopy. Freeze etchings, thin sections, and optical diffraction analysis of negatively stained fragments indicated that they consisted of two sets of a thin layer which was studied with 3-nm particles arranged in a loose (OL). The OSL consisted of a hexagonal arrangement of 8-nm disks and the OL of a thin layer which was studied with 3-nm particles arranged in a loose rectangular manner. The OSL of reassembled fragments displayed numerous broken delta-linkers between units and a center-to-center spacing of half the expected distance, which suggests that an interdigitation of two OSL arrays had occurred. The observations combined with freeze etchings and thin sections of whole cells suggested a possible reassembly mechanism. The normal surface arrangement of these layers on cells was thought to consist of the OL overlying one set of OSL which was loosely adherent to a thin amorphous backing layer.

Cell Membrane↗