PubMed Health⌕ Search

Biomedical subjects

W P Williams

Publications and source records attributed to W P Williams.

At least 19 recordsLinked to original sources
PubMed2005

Degradation of the S. frugiperda peritrophic matrix by an inducible maize cysteine protease.

A unique 33-kDa cysteine protease (Mir1-CP) rapidly accumulates at the feeding site in the whorls of maize (Zea mays L.) lines that are resistant to herbivory by Spodoptera frugiperda and other lepidopteran species. When larvae were reared on resistant plants, larval growth was reduced due to impaired nutrient utilization. Scanning electron microscopy (SEM) indicated that the peritrophic matrix (PM) was damaged when larvae fed on resistant plants or transgenic maize callus expressing Mir1-CP. To directly determine the effects of Mir1-CP on the PM in vitro, dissected PMs were treated with purified, recombinant Mir1-CP and the movement of Blue Dextran 2000 across the PM was measured. Mir1-CP completely permeabilized the PM and the time required to reach full permeability was inversely proportional to the concentration of Mir1-CP. Inclusion of E64, a specific cysteine protease inhibitor prevented the damage. The lumen side of the PM was more vulnerable to Mir1-CP attack than the epithelial side. Mir1-CP damaged the PM at pH values as high as 8.5 and more actively permeabilized the PM than equivalent concentrations of the cysteine proteases papain, bromelain and ficin. The effect of Mir1-CP on the PMs of Helicoverpa zea, Danaus plexippus, Ostrinia nubilalis, Periplaneta americana and Tenebrio molitor also was tested, but the greatest effect was on the S. frugiperda PM. These results demonstrate that the insect-inducible Mir1-CP directly damages the PM in vitro and is critical to insect defense in maize.

Animals↗
PubMed2001

Antimicrobial effectiveness of electro-chemically activated water as an endodontic irrigation solution.

AIM: The aim of this in vitro study was to evaluate the antimicrobial effectiveness of electro-chemically activated water (ECA) as an endodontic irrigation solution. METHODOLOGY: The root canals of 60 caries-free, single-rooted, adult, maxillary, anterior human teeth were instrumented and irrigated in a similar method to that used for in vivo root canal treatment. The external root surface of each tooth was sealed, maintaining the access cavities patent and the root canals were inoculated with a suspension containing four bacteria. The teeth were randomly divided into four groups (n = 15). Each group was irrigated ultrasonically with one of the following solutions: distilled water (control), NaOCl (3.5%), and ECA, the latter at pHs 7.0 and 9.0. Antimicrobial effectiveness was established directly after irrigation and again 7 days later, by counting colony-forming units on blood agar plates and by spectrophotometric analysis. RESULTS: Large numbers of bacteria were present in the canals of teeth irrigated with distilled water. No bacteria were observed following irrigation with NaOCl. Neither of the ECA solutions were found to be effective against all the bacteria. Although some reduction in the number of bacteria was evident in the ECA groups, this was not statistically significant (P > 0.05) when compared to sodium hypochlorite. CONCLUSION: Within the confines of this study ECA did not demonstrate antimicrobial effectiveness.

Adult↗
PubMed2000

A unique 33-kD cysteine proteinase accumulates in response to larval feeding in maize genotypes resistant to fall armyworm and other Lepidoptera.

Plants respond to insect feeding with a number of defense mechanisms. Using maize genotypes derived from Antiquan germ plasm that are resistant to Lepidoptera, we have demonstrated that a unique 33-kD cysteine proteinase accumulates in the whorl in response to larval feeding. The abundance of the proteinase increased dramatically at the site of larval feeding after 1 hr of infestation and continued to accumulate for as long as 7 days. The 33-kD cysteine proteinase was most abundant in the yellow-green portion of the whorl-the normal site of larval feeding and the tissue that has the greatest inhibitory effect on larval growth in bioassays. The proteinase was expressed in response to wounding and was found in senescent leaves. It may be a marker of programmed cell death. The gene coding for the proteinase, mir1, has been transformed into Black Mexican Sweet callus. When larvae were reared on callus expressing the proteinase, their growth was inhibited approximately 60 to 80%. The expression of a cysteine proteinase, instead of a cysteine proteinase inhibitor, may be a novel insect defense mechanism in plants.

Animals↗
PubMed2000

Influence of whorl region from resistant and susceptible corn genotypes on fall armyworm (Lepidoptera: Noctuidae) growth and development.

The effect of diets prepared from whorl tissue of resistant and susceptible corn genotypes, Zea mays L., on the larval growth, development, and physiology of fall armyworm, Spodoptera frugiperda (J. E. Smith), was analyzed. Larvae reared on an optimized artificial diet had a higher growth rate and developed faster than those reared on lyophilized whorl tissue from resistant and susceptible genotypes. Larvae reared on the resistant material were smaller and had a longer developmental period. Larvae reared on yellow-green and green whorl sections from resistant plants were significantly smaller than those reared on the same sections of susceptible plants. There was no significant difference in weight when larvae were reared on the yellow whorl regions from either resistant or susceptible lines. Physiological indices were determined for larvae fed resistant and susceptible lyophilized and fresh whorl material. Larvae fed resistant lyophilized material had significantly lower growth rate (GW) and efficiency of conversion of ingested food to body substance (ECI) than those reared on artificial diet or susceptible material. However, there were no significant differences in consumption index (CI), approximate digestibility (AD) and efficiency of conversion of digested food to body substance (ECD) between larvae reared on lyophilized tissue from resistant and susceptible genotypes. Larvae reared on fresh yellow-green whorl sections from resistant plants had significantly lower GW, ECI, and ECD than those reared on susceptible material. In contrast, no significant differences in any of the estimated food consumption and utilization indices were observed between larvae reared on fresh yellow whorl sections from resistant or susceptible plants. These results suggest that some components of whorls from resistant plants, especially the yellow-green region, inhibit food utilization in fall armyworm larvae.

Animals↗
PubMed2000

Amelogenesis imperfecta: functional and esthetic restoration of a severely compromised dentition.

The treatment of patients with severe forms of amelogenesis imperfecta presents an interesting challenge to the dental team. A 16-year-old girl presented with a severely compromised occlusion and poor esthetics that had lowered her self-esteem. Preoperative investigations included the determination of completion of growth, an accurate diagnostic waxup, and an evaluation of clinical crown lengths. Periodontal full-flap surgery was planned to lengthen clinical crowns and create gingival harmony. This was to be followed by placement of 28 complete crowns to restore occlusal function and gain a pleasing esthetic result. All-porcelain crowns were placed from premolar to premolar in each arch (20 crowns), and porcelain-fused-to-metal crowns were placed on each molar tooth in each arch (8 crowns). The final treatment result provided this patient with a mutually protective occlusion and with esthetics that greatly enhanced her self-image.

Adolescent↗
PubMed1999

Characterization of three distinct cDNA clones encoding cysteine proteinases from maize (Zea mays L.) callus.

In previous work, a 33 kDa cysteine proteinase was found in callus initiated from maize (Zea mays L.) resistant to fall armyworm feeding. A callus cDNA library from the maize inbred Mp708 was screened with oligonucleotides derived from the N-terminal amino acid sequence of the 33 kDa proteinase and several cDNA clones were isolated and sequenced. A cDNA clone encoding the 33 kDa cysteine proteinase, mir1, was identified. Two additional clones, mir2 and mir3, encoding putative cysteine proteinases were also identified. mir2 and mir3 are distinct from mir1 and each other, but show a high degree of homology. All of the mir cDNA clones map to distinct sites on the maize genome. Amino acid sequences encoded by the mir clones are similar to other known cysteine proteinases and are most closely related to the oryzain-alpha and -beta precursors. The ERFNIN motif and a 12 amino acid conserved sequence are present in the propeptide region of the putative proteinases encoded by mir clones. mir2 and mir3 appear to have C-terminal extensions. The phylogenetic tree of nucleotide sequences of mir1, mir2, mir3 and other representative cysteine proteinases from protozoa, plants and animals was constructed.

Amino Acid Sequence↗
PubMed1998

X-ray diffraction studies of the structural organisation of prolamellar bodies isolated from Zea mays.

Transmission electron microscopy (TEM) indicates that maize prolamellar bodies (PLBs) are built up of tetrapodal units based on a highly convoluted but continuous lipid bilayer exhibiting diamond cubic (Fd3m) symmetry. Such lattices are often described in terms of infinite periodic minimal surfaces (IMPS) exhibiting zero net curvature and dividing the system into two identical subvolumes. If so, X-ray diffraction measurements would be expected to index on a double-diamond (Pn3m) lattice with a unit cell length half that of the TEM lattice. Our measurements index on a Fd3m lattice with a similar repeat distance to the TEM images. The PLB membrane is thus inherently asymmetric, probably as the result of the distribution of membrane protein.

Darkness↗
PubMed1997

X-ray diffraction study of bilayer to non-bilayer phase transitions in aqueous dispersions of di-polyenoic phosphatidylethanolamines.

The low temperature phase properties of aqueous dispersions of di-18:2 and di-18:3 phosphatidylethanolamine are strongly influenced by the presence of ice. In the presence of cryoprotectants to inhibit ice formation, these lipids persist in the H(II) phase down to at least -50 degrees C. Ice formation, however, leads to a drastic reduction in the amount of available free water and a rapid reduction in the diameter of the inverted cylindrical micelles of the H(II) phase. The resulting increase in surface curvature of the micelles induces an imbalance in the forces acting in the lipid surface and the hydrophobic core which is relieved by formation of the L(alpha) phase. On reheating the lipid samples undergo an abrupt L(alpha) --> H(II) phase transition at about -20 degrees C. The radius of the water core of the inverted micelles at their point of formation is estimated to be 0.9 nm. This increases with temperature as more unfrozen water becomes available until the normal equilibrium radius of about 2.3 nm is reached at 0 degrees C when the bulk water in the sample finally melts. A small proportion of the H(II) phase lipid enters an as yet unidentified cubic phase on freezing. The spacings of the (10) planes of the H(II) phase, the (111) planes of the cubic phase and the d-spacing of the L(alpha) phase were found to be almost identical at the phase transition temperature. The cubic phase appears to disappear at low temperature but to reform on heating. Freeze-fracture studies revealed no unequivocal evidence for cubic phase lipid but the presence of residual non-bilayer lipid structures was observed even at temperatures as low as -80 degrees C. The presence of intersecting stacks of lamellar sheets in the replicas strongly suggest the existence of an epitaxial relationship between the L(alpha) and H(II) phases in these systems.

Freeze Fracturing↗
PubMed1996

A combined SAXS/WAXS investigation of the phase behaviour of di-polyenoic membrane lipids.

Real-time measurements of the SAXS/WAXS diffraction patterns of aqueous dispersions (1:1 wt/wt) of the di-polyenoic lipids di-18:2 PC, di-18:3 PC, di-18:2 PE and di-18:3 PE were made over the temperature range 10 degrees to about -80 degrees C. The results of these measurements were compared to similar measurements performed on the corresponding di-18:0 and di-18:1 derivatives. SAXS measurements of the temperature dependence of lamellar repeat distances show that the di-polyenoic lipids undergo broad second-order transitions between their gel and liquid-crystal lamellar phases spanning 30-40 degrees C. The di-18:1 and di-18:0 derivatives, in contrast, undergo abrupt first-order transitions. The gel phases of the di-18:0 derivatives are characterised by two-component WAXS patterns with a sharp component close to 0.42 nm and a broader component at narrower spacings. On cooling, these lipids appear to undergo an initial transition to an L beta, phase followed by a conversion to an Lc phase. The gel phases of the di-18:1 derivatives also show two-component patterns but with the sharp component centred closer to 0.44 nm. The di-polyenoic lipids, in contrast, are characterised by a single broad peak centred at a spacing of about 0.42 nm, close to that of conventional L beta phases. The changes in lamellar repeat distance accompanying the transitions in the di-monoenoic and di-polyenoic lipids, all of which occur in the frozen state, are very similar, indicating that the acyl chains of the polyenoic lipids are close to their maximum extension in the gel state. The WAXS patterns of the polyenoic lipids suggest that the saturated upper parts of the acyl chains are packed on a regular hexagonal lattice while their polyunsaturated termini remain relatively disordered.

Membrane Lipids↗
PubMed1996

Thermotropic properties of dioleoylphosphatidylethanolamine in aqueous dimethyl sulfoxide solutions.

The effect of dimethyl sulfoxide (DMSO) on the phase behavior and structural parameters of aqueous dispersions of 1,2-dioleoylglycerophosphoethanolamine (DOPE) was characterized using differential scanning calorimetry and time-resolved synchrotron X-ray diffraction. In the range of concentrations of DMSO in water up to 50 wt%, there was a progressive increase in the temperature of the lamellar gel to lamellar liquid-crystal phase transition temperature and a marked decrease in temperature of the transition to the hexagonal II phase. At DMSO concentrations greater than about 25 wt% a direct transition from lamellar gel to hexagonal II structure was observed. A partial phase diagram of the phospholipid in DMSO has been constructed from thermal and X-ray diffraction data. Concentrations of DMSO greater than 50 wt% resulted in the formation of several lamellar crystal phases and interdigitated phases. Phase transition sequences measured on heating included low-temperature exothermic transitions between the interdigitated phase and lamellar crystal phases and an endothermic transition at about 30 degrees C between a lamellar crystal and an interdigitated phase. This latter phase converted directly into an hexagonal II phase at a temperature of about 50 degrees C. On cooling, a second nonbilayer phase (I) first appeared which subsequently reorganized to form a mixture of interdigitated and lamellar crystal phases. The significance of this data in terms of its possible relevance to the biological role of DMSO is discussed.

Biophysical Phenomena↗
PubMed1995

Association of a 33-kilodalton cysteine proteinase found in corn callus with the inhibition of fall armyworm larval growth.

Protein patterns of callus from corn (Zea mays L.) inbreds that are either resistant or susceptible to fall armyworm (Spodoptera frugiperda [J.E. Smith]) were analyzed by two-dimensional electrophoresis. Fall armyworm larvae reared on callus initiated from resistant inbreds were significantly smaller than those reared on callus of susceptible inbreds. A 33-kD protein found in callus from the resistant inbreds Mp704 and Mp708 was absent in callus from the susceptible inbreds Tx601 and Ab24E. However, a 36-kD protein found in Ab24E callus immunoreacted with polyclonal antibody raised against the 33-kD protein. When Mp704 nonfriable callus changed to friable, larval growth was not inhibited and the 33-kD protein was absent. There was a significant negative correlation between the concentration of the 33-kD protein in the callus and the weight of the larvae feeding on the callus in the F2 progeny of Mp704 x Tx601. The N-terminal amino acid sequence of the 33-kD protein suggested that it was cysteine proteinase. Purification of the 33- (Mp708) and 36-kD (Ab24E) proteins indicated that they were both cysteine proteinases. The 33-kD cysteine proteinase had 7-fold higher specific activity than the 36-kD enzyme.

Amino Acid Sequence↗
PubMed1994

The solute permeability of thylakoid membranes is reduced by low concentrations of trehalose as a co-solute.

The different efficiencies of sucrose and trehalose in protecting isolated spinach (Spinacia oleracea L.) thylakoids against freeze-thaw damage is quantitatively related to their ability to reduce the solute loading of the vesicles during freezing. In the present paper we show that this effect is based on a reduction of the solute permeability of the membranes. Permeability was measured with 14C-labeled glucose at temperatures between 0 and 10 degrees C. Glucose permeability was reduced by both sucrose and trehalose, with trehalose effective at much lower concentrations than sucrose. An analysis of the temperature dependence of glucose permeability in the presence and absence of trehalose revealed that a 50% reduction in permeability resulted from a 10% increase in activation energy and a 30% decrease in activation entropy. Using the fluorescence probe 1,6-diphenyl-1,3,5-hexatriene (DPH), we found that the reduced permeability of the membranes in the presence of trehalose was unaccompanied by a reduction in lipid fluidity. This also excluded the possibility of a solute-induced liquid crystalline to gel phase transition. A reduced partitioning of the hydrophobicity-sensitive dye merocyanine 540 into thylakoids and into membranes containing 50% digalactosyldiacylglycerol in the presence of trehalose as compared to sucrose and glucose showed that the lipid headgroup region of these membranes became less accessible for solutes. No significant difference in merocyanine partitioning in the presence of trehalose as compared to sucrose or glucose was apparent when monogalactosyldiacylglycerol dispersions or phosphatidylcholine vesicles were investigated.

Cell Membrane Permeability↗
PubMed1993

The effect of ice on membrane lipid phase behaviour.

The effects of ice on the lipid phase behaviour of di-18:1 PE and di-18:2 PE were studied by comparing the behaviour of these lipids in supercooled and frozen dispersions. The presence of ice raised the onset temperature of the L alpha--> L beta phase transition of di-18:1 PE from -10 degrees C to -6.5 degrees C and increased its molar enthalpy from 6.1 to 8.5 kcal/mol but had little effect on the co-operativity of the transition. Real-time X-ray diffraction measurements of the HII--> L alpha phase transition of di-18:2 PE suggested that this transition could take place in the presence of ice but that the corresponding L alpha--> HII phase transition could not take place until the ice melted. Measurements of the temperature dependence of the d-spacing of di-18:1 PE and di-18:2 PC in frozen dispersions indicated that the amounts of unfrozen water in such dispersions changes significantly with temperature. It was concluded that the increases in onset temperature and molar enthalpy seen for the L alpha--> L beta transition of di-18:1 PE probably reflected the effects of osmotic dehydration. The main effect of ice in the case of the HII--> L alpha phase transition, however, appeared to be to limit the ability of the lipid to undergo structural reorganisation.

Calorimetry, Differential Scanning↗
PubMed1993

Phase behaviour of membrane lipids containing polyenoic acyl chains.

The low-temperature thermal behaviour of di-18:2 phosphatidylethanolamine (di-18:2 PE) is shown to be characterized by similar broad low-enthalpy transitions to those previously reported for polyenoic samples of phosphatidylcholines (Keough and Kariel (1987) Biochim. Biophys. Acta 902, 11-18), and monogalactosyldiacylglycerol (Sanderson and Williams (1992) Biochim. Biophys. Acta. 1107, 77-85). Real-time X-ray diffraction measurements indicate that these transitions correspond to transitions between the gel (L beta) and liquid-crystal (L alpha) phases of the lipids. The gel phase of these lipids is, however, much more loosely packed than the corresponding phases of membrane lipids containing monoenoic or fully-saturated acyl chains. The low enthalpy and reduced co-operativity of the L alpha--> L beta phase transitions of the polyenoic lipids is attributed to the reduced contribution of van der Waals interactions between their acyl chains in the gel-state of these lipids. Comparison with the earlier results obtained for MGDG suggest that the acyl chains of polyenoic lipids can form well-ordered lattices but require the additional energy input associated with the formation of a hydrogen bond network between the lipid headgroups in order to do so.

Calorimetry, Differential Scanning↗
PubMed1992

Low-temperature phase behaviour of the major plant leaf lipid monogalactosyldiacylglycerol.

Heating and cooling thermograms of unsaturated MGDG samples isolated from the leaves of Vicia faba are surprisingly featureless. This reflects the low enthalpies associated with phase transitions in highly unsaturated lipids and the fact that these transitions, in the case of MGDG, are to a large extent masked by those associated with the freezing and melting of ice. Careful choice of thermal heating/cooling regimes, combined with the use of real-time X-ray diffraction and freeze-fracture measurements, permits a detailed analysis of the phase behaviour of the system. The phase behaviour of unsaturated MGDG samples is shown to be basically similar to that seen in saturated MGDG samples. The lipid which exists in the inverted hexagonal (HexII) liquid crystal phase at room temperature forms a highly disordered lamellar gel (L beta) phase on cooling to temperatures below about -15 degrees C. On reheating, this first reorganizes at a temperature of about -10 degrees C to form a well-defined Lc1 phase. Above about -2 degrees C, this melts to re-form the HexII phase. Samples re-cooled from temperatures between -2 degrees C and 14 degrees C revert directly to the Lc1 phase while samples cooled from higher temperatures form the L beta phase. This reflects the fact that the former samples contain small amounts of unmelted Lc1 phase lipid. The implications of these observations are discussed in terms of the general problems associated with the measurement of low-temperature phase behaviour of membrane lipids.

Calorimetry, Differential Scanning↗