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Biomedical subjects

R L Williams

Publications and source records attributed to R L Williams.

At least 109 records · Page 6Linked to original sources
PubMed1998

Family practice in the new South Africa.

Remarkable changes are taking place in the new South Africa. Planned changes in the health care arena present the new, relatively small discipline* of family practice with great opportunity for development and growth. With established generalist roots and recent formal recognition in South Africa, family practice should be well suited for a lead role in the government's efforts to extend health care access to those denied it under apartheid. Whether family practice moves into that role will depend on whether as a discipline it can project a vision of how it can meet the country's health care needs. Close examination of family practice in South Africa shows how the field reflects many of the societal problems of the past and the challenges of the future. With a clear vision of its role in the new South Africa, family practice could overcome these challenges, as well as answer a broader question about the place of family practice outside of the first world setting.

Family Practice↗
PubMed1997

Phosphoinositide-specific phospholipase C delta1 activity toward micellar substrates, inositol 1,2-cyclic phosphate, and other water-soluble substrates: a sequential mechanism and allosteric activation.

The kinetics of full-length and PH domain truncated cloned PI-PLC delta1 from rat toward soluble substrates [inositol 1, 2-(cyclic)-phosphate (cIP) and glycerophosphoinositol phosphates (GPIPx)] as well as PI in detergent micelles provide the following insights into the mechanism of this enzyme. (i) That cIP is a substrate for the enzyme implies a two-step mechanism for PI hydrolysis [intramolecular phosphotransferase reaction to form cIP followed by cyclic phosphodiesterase activity to form inositol-1-phosphate (I-1-P)]. The dependence of enzyme activity on cIP is sigmoidal, suggesting a transition between less active and more active forms of the enzyme that is affected by substrate. (ii) Interfaces increase the kcat for cIP (but do not affect the cooperativity), and this allosteric activation requires an intact PH domain. (iii) Phosphorylation of the soluble inositol phosphodiesters GPI, GPIP, and GPIP2 enhances PI-PLC delta1 activity by dramatically increasing kcat and decreasing Km. For these phosphodiesters, the substrate saturation curve is no longer sigmoidal but hyperbolic, indicating the phosphorylated substrate can shift the enzyme to the activated form. (iv) Given the kinetic parameters for cIP hydrolysis and the constant ratio of cIP/I-1-P generated during PI hydrolysis, the cIP produced in situ is either released (and not readily rebound since its concentration is well below Km) or attacked by a water molecule for the generation of the acyclic product.

Allosteric Regulation↗
PubMed1997

The 2.0-A resolution crystal structure of a trimeric antibody fragment with noncognate VH-VL domain pairs shows a rearrangement of VH CDR3.

The 2.0-A resolution x-ray crystal structure of a novel trimeric antibody fragment, a "triabody," has been determined. The trimer is made up of polypeptides constructed in a manner identical to that previously described for some "diabodies": a VL domain directly fused to the C terminus of a VH domain-i.e., without any linker sequence. The trimer has three Fv heads with the polypeptides arranged in a cyclic, head-to-tail fashion. For the particular structure reported here, the polypeptide was constructed with a VH domain from one antibody fused to the VL domain from an unrelated antibody giving rise to "combinatorial" Fvs upon formation of the trimer. The structure shows that the exchange of the VL domain from antibody B1-8, a Vlambda domain, with the VL domain from antibody NQ11, a Vkappa domain, leads to a dramatic conformational change in the VH CDR3 loop of antibody B1-8. The magnitude of this change is similar to the largest of the conformational changes observed in antibody fragments in response to antigen binding. Combinatorial pairing of VH and VL domains constitutes a major component of antibody diversity. Conformationally flexible antigen-binding sites capable of adapting to the specific CDR3 loop context created upon VH-VL pairing may be employed by the immune system to maximize the structural diversity of the immune response.

Amino Acid Sequence↗
PubMed1997

Expression of dihydropyridine binding sites in renal epithelial cells.

It has recently been shown that rabbit kidney epithelial cells (proximal tubule) possess two dihydropyridine (DHP)-sensitive calcium entry channels (1, 2). To evaluate the properties of the DHP binding sites, the binding of the DHP, [3H]PN200-110, was studied in epithelial cell membrane fractions (proximal tubule) of rabbit kidney cortex. High-affinity binding sites for the DHP were observed in both basolateral and apical membranes and in a membrane microsomal preparation from rabbit primary cultures of proximal tubule cells (cultured PT). In an extended analysis of the basolateral membrane preparation, two high-affinity binding sites were evident with binding dissociation constants, Kd, of 0.005 and 0.75 nM. The Kd values are similar to that observed for L-type calcium channel alpha1-subunits. Using a homology-based cloning strategy, a 388-base fragment of an alpha1-subunit was cloned from RNA isolated from rabbit cultured PT cells and freshly isolated proximal tubules and found to encode a protein identical to the cardiac form of the L-type alpha1-subunit (alpha1C-subunit). It is concluded that renal epithelial cells express high-affinity dihydropyridine receptors and that the receptors may be components of plasma membrane calcium channels, including L-type calcium channels, that control calcium entry in these cells.

Amino Acid Sequence↗
PubMed1997

A ternary metal binding site in the C2 domain of phosphoinositide-specific phospholipase C-delta1.

We have determined the crystal structures of complexes of phosphoinositide-specific phospholipase C-delta1 from rat with calcium, barium, and lanthanum at 2.5-2.6 A resolution. Binding of these metal ions is observed in the active site of the catalytic TIM barrel and in the calcium binding region (CBR) of the C2 domain. The C2 domain of PLC-delta1 is a circularly permuted topological variant (P-variant) of the synaptotagmin I C2A domain (S-variant). On the basis of sequence analysis, we propose that both the S-variant and P-variant topologies are present among other C2 domains. Multiple adjacent binding sites in the C2 domain were observed for calcium and the other metal/enzyme complexes. The maximum number of binding sites observed was for the calcium analogue lanthanum. This complex shows an array-like binding of three lanthanum ions (sites I-III) in a crevice on one end of the C2 beta-sandwich. Residues involved in metal binding are contained in three loops, CBR1, CBR2, and CBR3. Sites I and II are maintained in the calcium and barium complexes, whereas sites II and III coincide with a binary calcium binding site in the C2A domain of synaptotagmin I. Several conformers for CBR1 are observed. The conformation of CBR1 does not appear to be strictly dependent on metal binding; however, metal binding may stabilize certain conformers. No significant structural changes are observed for CBR2 or CBR3. The surface of this ternary binding site provides a cluster of freely accessible liganding positions for putative phospholipid ligands of the C2 domain. It may be that the ternary metal binding site is also a feature of calcium-dependent phospholipid binding in solution. A ternary metal binding site might be a conserved feature among C2 domains that contain the critical calcium ligands in their CBR's. The high cooperativity of calcium-mediated lipid binding by C2 domains described previously is explained by this novel type of calcium binding site.

Animals↗
PubMed1997

Structural mapping of the catalytic mechanism for a mammalian phosphoinositide-specific phospholipase C.

The crystal structures of various ternary complexes of phosphoinositide-specific phospholipase C-delta 1 from rat with calcium and inositol phosphates have been determined at 2.30-2.95 A resolution. The inositol phosphates used in this study mimic the binding of substrates and the reaction intermediate and include D-myo-inositol-1,4,5-trisphosphate, D-myo-inositol-2,4, 5-trisphosphate. D-myo-inositol-4,5-bisphosphate, and D,1-myo-inositol-2-methylene-1,2-cyclićmonophosphonate. The complexes exhibit an almost invariant mode of binding in the active site, each fitting edge-on into the active site and interacting with both the enzyme and the catalytic calcium at the bottom of the active site. Most of the active site residues do not undergo conformational changes upon binding either calcium or inositol phosphates. The structures are consistent with bidentate liganding of the catalytic calcium to the inositol phosphate intermediate and transition state. The complexes suggest explanations for substrate preference, pH optima, and ratio of cyclic to acyclic reaction products. A reaction mechanism is derived that supports general acid/base catalysis in a sequential mechanism involving a cyclic phosphate intermediate and rules out a parallel mechanism where acyclic and cyclic products are simultaneously generated.

Animals↗
PubMed1997

A study of cell behaviour on the surfaces of multifilament materials.

Since many fibres are very strong, they are considered to have useful potential for fibre reinforcement of orthopaedic and dental implant materials. Fibres exposed on the surface of composites may significantly influence the cellular response not only due to the chemistry but also due to the fibre size and shape. This study has concentrated on investigation of cellular responses to fibre-specific aspects of fibre-reinforced composites. Four multifilament materials with diameter less than 20 microm were used: Kevlar 29(K), silicon carbide(SiC), nylon 66(N), and polyethylene terephthalate(PET). Established cell line L929 fibroblasts were used as the cell model. Cell behaviour on the surfaces of fibres was examined using direct cell counting (after 3, 5, 8 h and 1, 2, 3 days), scanning electron microscopy (SEM) (after 2 h and 2 days), and fluorescent staining of F-actin, which was analysed by confocal laser scanning microscopy (CLSM) (after 2 h and 2 days). The results showed that fibroblasts adhered and grew very well on all fibre surfaces, although less cells were observed on PET from direct cell counting. Significant orientational behaviour of cells was found on all fibre surfaces from the SEM and CLSM analysis, independent of the bulk chemistry of the fibres.

Journal Article↗
PubMed1997

Hyperbaric oxygen therapy and the diabetic foot.

Hyperbaric oxygen therapy is an adjunctive wound-healing modality receiving increasing use for problem wounds, particularly diabetic foot wounds. Nevertheless, few clinicians understand the physiologic basis for this modality; how patients are selected, or the expected results. The author reviews the development of hyperbaric oxygen therapy, selection of patients, and clinical studies of this modality for diabetic patients with foot wounds.

Diabetic Foot↗
PubMed1997

The Rotaflex total knee replacement--a 5 year review.

We report the results of a retrospective analysis of 43 patients who received 56 Rotaflex total knee arthroplasties, with a mean follow-up of 55.7 months. The British Orthopaedic Association (BOA) knee assessment protocol was used in evaluating the clinical results. Two patients could not receive post-operative scores. In the remaining 54 knees, the mean pre-operative score was 25.6, improving to 30.8 post-operatively. Ten knees showed a decrease in knee score, two were unchanged and 42 improved. The greatest improvements were in pain relief and maximum flexion. Wound infection and dehiscences were common, the latter requiring further surgery in five cases. Later, there were eight fractures involving the prosthesis, seven dislocated or subluxed patellae, two deep infections and three cases of severe aseptic loosening. A common feature was severe patellar wear, due to the design fault of an absent femoral groove. The high rate of complications and poor functional result of the Rotaflex knee preclude its use in current practice.

Activities of Daily Living↗
PubMed1997

Improving transfusion practices in a busy teaching hospital.

A retrospective audit of blood transfusions was carried out in Cardiff Royal Infirmary (CRI) to investigate how efficiently blood was requested and used by the various clinical directorates. Excessive crossmatch/transfusion (C/T) ratios were found for a number of operations. In an attempt to improve practices, a pilot study was carried out between the Department of Haematology and the largest single requesting group, the Orthopaedic Directorate. As a result of a preliminary retrospective audit, crossmatch guidelines were revised, with more reliance on the group and antibody screen (G & S) for low-risk operations. A subsequent prospective audit showed major reductions in crossmatch requests and a general decrease in C/T ratios to very efficient levels without any patient morbidity. Blood was freed for urgent use elsewhere, and significant cost improvements resulted. This study, using the orthopaedic surgery department as a model, shows the value of inter-departmental audit and supports the experience of other centres using similar methods to make considerable savings in the amount of blood crossmatched unnecessarily.

Blood Banks↗
PubMed1997

JCAHO accreditation. Is it necessary?

Many hospital leaders question the need for accreditation from the Joint Commission on Accreditation of Healthcare Organizations (JCAHO). Unhappy with the JCAHO and its accreditation process, hospital executives are looking at alternatives. State and federal governments, managed care organizations and hospitals monitoring themselves all have the potential to replace accreditation. This article looks at these alternatives from a nursing perspective.

Accreditation↗
PubMed1996

Structural views of phosphoinositide-specific phospholipase C: signalling the way ahead.

Recent structural studies of mammalian phosphoinositide-specific phospholipase C (PI-PLC) have begun to shed light on the mechanism whereby this family of effector enzymes is able to hydrolyze phospholipid substrates to yield second messengers. PI-PLC isozymes employ a variety of modules (PH domain, EF-hand domain, SH2 domain, SH3 domain and C2 domain) that are common in proteins involved in signal transduction to reversibly interact with membranes and protein components of the signalling pathways.

Binding Sites↗
PubMed1996

Crystal structure of a mammalian phosphoinositide-specific phospholipase C delta.

Mammalian phosphoinositide-specific phospholipase C enzymes (PI-PLC) act as signal transducers that generate two second messengers, inositol-1,4,5-trisphosphate and diacylglycerol. The 2.4-A structure of phospholipase C delta 1 reveals a multidomain protein incorporating modules shared by many signalling proteins. The structure suggests a mechanism for membrane attachment and Ca2+-dependent hydrolysis of second-messenger precursors. The regulation and reversible membrane association of PI-PLC may serve as a model for understanding other multidomain enzymes involved in phospholipid signalling.

Amino Acid Sequence↗
PubMed1996

Towards a practical strategy for assessing individual bioequivalence. Food and Drug Administration Individual Bioequivalence Working Group.

Bioequivalence of two drug formulations is currently defined by drug regulatory authorities in terms of the mean responses following administration of the test and reference formulations (average bioequivalence). However, the various potential shortcomings of average bioequivalence are now understood, and switchability, and thus individual bioequivalence, has become a reasonable expectation when changing from one pharmaceutically equivalent drug product to another. Progress has been made in developing criteria for individual bioequivalence, and an overview and classification of most of the different approaches to the assessment of individual bioequivalence have been achieved. As a consequence of this classification, the different character of scaled and unscaled bioequivalence measures has been recognized and, in turn, this leads to the proposal, made in this paper, of using both scaled and unscaled criteria for bioequivalence assessment of different classes of drugs, depending on their within-subject variability and therapeutic range. This strategy addresses the shortcomings of average bioequivalence, and, when applied to data sets from bioequivalence studies with four-period replicate crossover designs, turns out to have some satisfactory properties. Open questions and areas for further research are discussed.

Biological Availability↗
PubMed1996

The check X-ray: an unnecessary investigation after hip fracture fixation?

An X-ray-based image intensification system is a necessary operative aid in many orthopaedic procedures. Technological advances have not only increased the resolution of these systems, but allow the production of thermal images. We have compared such images obtained at the time of surgery with postoperative radiographs in 80 patients who underwent closed reduction and internal fixation for proximal femoral fractures. The films were independently assessed with particular reference to fracture reduction and the adequacy of fixation. In no case did the postoperative radiograph provide additional information. We therefore suggest that a postoperative radiograph is only necessary in exceptional circumstances. This is of significance in relation to patient discomfort, morbidity and radiation exposure. It also has important financial and manpower implications.

Bone Screws↗