Are pencil point needles safe for subarachnoid block?
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Anesthesia, Spinal↗
Biomedical subjects
M A Turner
Publications and source records attributed to M A Turner.
Structural comparison of the enzymatically active and inactive forms of delta crystallin and the role of histidine 91.
The major soluble protein component of avian and reptilian eye lenses, delta crystallin, is highly homologous to the urea cycle enzyme, argininosuccinate lyase (ASL). In duck lenses there are two highly homologous delta crystallins, termed delta I and delta II, that are 94% identical in amino acid sequence. While delta II crystallin has been shown to exhibit ASL activity in vitro, delta I crystallin is inactive. The X-ray structure of a His to Asn mutant of duck delta II crystallin (H91N) has been determined to 2.5 A resolution using the molecular replacement technique. The overall fold of the protein is similar to other members of the superfamily to which this protein belongs, with the active site located in a cleft between three different monomers of the tetrameric protein. A reexamination of the kinetic properties of the H91N mutant reveals that the mutant has 10% wild-type activity. The Vmax of the mutant protein is identical to that of the wild-type protein, but a 10-fold increase in the Michaelis constant is seen, suggesting that His 91 is involved in binding the substrate. In an effort to determine the reasons for the loss of enzymatic activity in delta I crystallin, a structural comparison of the H91N mutant with the enzymatically inactive turkey delta I crystallin has been performed. This study revealed a remarkable similarity in the overall structures of the two proteins. Three regions of secondary structure do differ significantly between the two models; these include the N-terminal tail, a loop containing residues 76-91, and a cis versus trans peptide linkage at residue Thr 322. The cis to trans peptide variation appears to be an interspecies difference between turkey and duck and is therefore not directly involved in the loss of enzymatic activity. All the residues implicated in the catalytic mechanism are conserved in both the active and inactive proteins, and given the linearity of the relationship between the enzymatic activity of duck delta I/delta II heterotetramers and their delta II content (Piatigorsky & Horwitz, 1996), it is evident from the structure that only one of the three domains that contributes to the active site is responsible for the loss of activity in the delta I protein. Given the structural differences found in domain 1 (N-terminal tail and 76-91 loop), we postulate that these differences are responsible for the loss of catalytic activity in the delta I crystallin protein and that the delta I protein is inactive because it no longer binds the substrate.
Amino Acid Sequence↗
Human argininosuccinate lyase: a structural basis for intragenic complementation.
Intragenic complementation has been observed at the argininosuccinate lyase (ASL) locus. Intragenic complementation is a phenomenon that occurs when a multimeric protein is formed from subunits produced by different mutant alleles of a gene. The resulting hybrid protein exhibits enzymatic activity that is greater than that found in the oligomeric proteins produced by each mutant allele alone. The mutations involved in the most successful complementation event observed in ASL deficiency were found to be an aspartate to glycine mutation at codon 87 of one allele (D87G) coupled with a glutamine to arginine mutation at codon 286 of the other (Q286R). To understand the structural basis of the Q286R:D87G intragenic complementation event at the ASL locus, we have determined the x-ray crystal structure of recombinant human ASL at 4. 0 A resolution. The structure has been refined to an R factor of 18. 8%. Two monomers related by a noncrystallographic 2-fold axis comprise the asymmetric unit, and a crystallographic 2-fold axis of space group P3121 completes the tetramer. Each of the four active sites is composed of residues from three monomers. Structural mapping of the Q286R and D87G mutations indicate that both are near the active site and each is contributed by a different monomer. Thus when mutant monomers combine randomly such that one active site contains both mutations, it is required by molecular symmetry that another active site exists with no mutations. These "native" active sites give rise to the observed partial recovery of enzymatic activity.
Alleles↗
Crystallization and preliminary X-ray analysis of human placental S-adenosylhomocysteine hydrolase.
A recombinant form of human placental S-adenosylhomocysteine (AdoHcy) hydrolase expressed in E. coli, which was inactivated by a type-I mechanism-based inhibitor, has been crystallized using the hanging-drop vapour-diffusion technique. The crystals grow as flat plates, with unit-cell dimensions a = 96.2, b = 173.6, c = 142.9 A, alpha = beta = gamma = 90 degrees. The crystals exhibit the symmetry of space group C222 and diffract to a minimum spacing of approximately 2.0 A resolution at the Cornell High Energy Synchrotron Source. On the basis of density calculations two monomers of the tetrameric protein are estimated to be present in the asymmetric unit (V(m) = 2.99 A(3) Da(-l)). The self-rotation function clearly indicates the location of the non-crystallographic twofold axis.
Journal Article↗
Molecular characterization of the prokaryotic efp gene product involved in a peptidyltransferase reaction.
The translation factor EF-P is required for efficient prokaryotic peptide bond synthesis on 70S ribosomes from fMet-tRNAfMet. This protein has been purified from Escherichia coli cells and the gene, efp, encoding it has been cloned and sequenced. We have isolated recombinant clones which overexpress a protein that co-migrates with purified EF-P upon SDS-PAGE analysis. Using these clones, we report the purification, crystallization and initial characterization of the efp gene product. The mechanism by which EF-P stimulates peptide-bond synthesis was studied using several antibiotics that inhibit translocation, peptide-bond synthesis and decoding. The stimulation of peptidyltransferase by EF-P was not inhibited by antibiotics that affect translocation and occupation of the A site (in the elongation state), ie thiostrepton, viomycin, neomycin and fusidic acid but was inhibited by streptomycin as well as by inhibitors of peptidyltransferase, chloramphenicol and lincomycin. This observation and the requirement for L16 but not for the L7/L12 nor L6 or L11 r-proteins suggest that the binding site for EF-P may overlap the peptidyltransferase center of the ribosome.
Anti-Bacterial Agents↗
Epithelial-stromal interactions modulating penetration of matrigel membranes by HPV 16-immortalized keratinocytes.
The role of epithelial-stromal interactions in the progression of human papillomavirus-associated squamous intraepithelial lesions to invasive cervical cancer is poorly understood. Using the Matrigel artificial basement membrane assay as a model of keratinocyte invasion, the effects of selected growth factors on penetration of human papillomavirus 16-immortalized keratinocytes through Matrigel were studied. Also studied in this model were the effects of conditioned media from fibroblast lines derived from normal cervical tissues (normal fibroblasts) and adjacent cervical cancer biopsies (tumor-associated fibroblasts) and from primary keratinocytes. Addition of basic fibroblast growth factor, transforming growth factor-alpha, and hepatocyte growth factor/scatter factor or conditioned media from tumor-associated fibroblasts to the Matrigel resulted in near-doubling of penetration of human papillomavirus 16-immortalized keratinocytes, whereas transforming growth factor-beta, platelet derived growth factor-B, or conditioned media from primary keratinocytes decreased penetration 10-fold. Antibodies to basic fibroblast growth factor abrogated the stimulatory effects of conditioned media from tumor-associated fibroblasts on keratinocyte penetration, whereas antibodies to transforming growth factor-beta abrogated the inhibitory effects of conditioned media from normal fibroblasts on keratinocyte penetration. S1 nuclease protection and enzyme-linked immunosorbent assay showed increased expression of transforming growth factor-beta and decreased expression of basic fibroblast growth factor in normal compared with tumor-associated fibroblasts. Messenger RNA in situ hybridization of five cervical cancer biopsies demonstrated basic fibroblast growth factor expression in stromal cells surrounding nests of invading keratinocytes. Epithelial-stromal interactions mediated by growth factors such as transforming growth factor-beta and basic fibroblast growth factor modulate penetration of human papillomavirus 16-immortalized keratinocytes through Matrigel in vitro and these interactions may also be operative in vivo.
Basement Membrane↗
Joint disorders in cystic fibrosis.
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Arthritis↗
HASTE MR cholangiography in the evaluation of hilar cholangiocarcinoma.
OBJECTIVE: The objective of this study was to determine the usefulness of MR cholangiography using the half-Fourier acquisition single-shot turbo spin-echo sequence in the examination of patients with hilar cholangiocarcinoma. CONCLUSION: Half-Fourier acquisition single-shot turbo spin-echo MR cholangiography is a useful, noninvasive adjunct to other imaging techniques, particularly MR imaging, in the evaluation of hilar cholangiocarcinoma. MR cholangiography allows rapid visualization of the biliary tract without instrumentation and, therefore, without the risk of inducing sepsis in a patient with ductal obstruction. In the six patients presented. MR cholangiography allowed for determination of the proximal extent of disease and assessment of resectability and delineated the duct both proximal and distal to the stricture and isolated ductal obstructions. MR cholangiography provides three-dimensional images of the biliary tract that facilitate planning of surgery, palliative drainage, and radiation therapy.
Aged↗
Nutrition measures for managed care report cards.
Health plan "report cards," that is, published summaries of health plan performance, are a new way to help consumers select a health plan on the basis of cost and quality. The Health Plan Employer Data and Information Set (HEDIS) includes a set of health plan performance measures, standardized definitions, and methods for data collection. HEDIS is used as the basis for many report card initiatives and is the preferred tool of the managed care industry for measuring health plan performance. Nevertheless, the current list of HEDIS performance measures omits many health services, including medical nutrition therapy. Nutrition measures have the potential for wide appeal among health care stakeholders (ie, payers, consumers, and providers). Four measures related to medical nutrition therapy are proposed for managed care report cards: staffing for nutrition services and medical nutrition therapy for high cholesterol level, gestational diabetes, and cardiovascular disease. Barriers to adopting medical nutrition therapy measures in HEDIS include the need to address technical issues before considering new measures and competition from other potential measures. Steps to create support for medical nutrition therapy measures in HEDIS should focus on influencing representatives of health plans and employers to include these measures. The involvement of registered dietitians in the dynamic process of health plan evaluation is an important extension of ongoing efforts for strategic positioning in the managed care market.
Dietary Services↗
Gastrointestinal tract involvement by gynecologic diseases.
Involvement of the gastrointestinal tract by gynecologic disease processes-endometriosis, gynecologic neoplasms, inflammatory processes, and complications from radiation therapy or surgery for gynecologic tumors-may mimic primary gastrointestinal carcinoma on radiologic images. Endometriosis most often involves the anterior wall of the rectosigmoid colon, adjacent to the pouch of Douglas, and typically produces extrinsic mass effect on the serosa, with the overlying mucosa left intact. Direct extension of ovarian cancer to the colon through the subperitoneal space produces mass effect with serosal spiculation, tethering, and fixation; annular constriction; or partial or complete obstruction. Intraperitoneal seeding of ovarian carcinoma most frequently involves the colon and is seen as extrinsic masses, often with serosal spiculation and tethering. Cervical carcinoma, which most commonly spreads by direct invasion of the pelvic side wall and adjacent structures, produces serosal spiculation and circumferential narrowing. Benign ovarian or uterine tumors are purely extrinsic and have a smooth interface with the colonic wall. Tubo-ovarian abscesses are difficult to differentiate from cystic ovarian neoplasms or endometriomas. Radiation colitis causes narrowing of the rectum with intact mucosa and can be differentiated from recurrent tumor, unlike radiation-induced injury of the small bowel, which may be difficult to distinguish. Surgical adhesions produce a discrete transition point between dilated bowel proximally and nondilated distal bowel. Familiarity with the varied patterns of gastrointestinal tract involvement is important for accurate interpretation of imaging studies.
Diagnosis, Differential↗
Percutaneous drainage of enteric-related abscesses.
Percutaneous drainage is a routinely performed radiologic procedure used in the management of abdominal abscesses. This technique has become the preferred method of treatment for most abdominal and pelvic abscesses, specifically those of enteric origin related to surgical procedures, appendicitis, diverticulitis, and Crohn disease. The well-documented safety and therapeutic efficacy of percutaneous abscess drainage (PAD) lead to the acceptance of this procedure as the primary means of managing abdominal abscesses, obviating the need for surgery in many instances. PAD may provide definitive therapy or may serve as a temporizing measure before delayed surgical treatment. Although PAD was originally reserved for treatment of unilocular, relatively superficial fluid collections, the role of PAD has evolved such that it is now used to manage complex multilocular fluid collections and abscesses that lie deep within the abdomen or pelvis. Although the standard transabdominal approach is preferred, a variety of approaches, including transgastric, transrectal, transvaginal, and transgluteal, may be used. PAD is performed using CT or sonographic guidance.
Abdominal Abscess↗
Structures of partridge egg-white lysozyme with and without tri-N-acetylchitotriose inhibitor at 1.9 A resolution.
The three-dimensional structures of native partridge egg-white lysozyme (PEWL) and PEWL complexed with tri-N-acetylchitotriose inhibitor have been determined crystallographically and refined at 1.9 A resolution. Crystals of native and complexed protein are isomorphous and have space group and cell dimensions that are identical to those of hen egg-white lysozyme (HEWL) under similar crystallization conditions. Full occupancy of the trisaccharide in the inhibitor complex has allowed definitive modeling and refinement of all three sugar residues, located at subsites A, B, and C in the PEWL active site. A comparison has been made with HEWL/inhibitor complexes in which coordinates were either not refined (Blake CCF, et al., 1967, Proc R Soc B 167:378-388) or were refined at partial occupancy (Cheetham JC, Artymiuk PJ, Phillips DC, 1992, J Mol Biol 224:613-628). Although the loop comprising residues 70-75 is located on the surface of the protein and not near the active site, it appears to be affected indirectly by trisaccharide binding such that the loop shifts toward the active site and becomes relatively immobilized. The source of this loop movement appears to be the anchoring of Trp62, located in the active site cleft, as it forms a hydrogen bond with O6 of the N-acetylglucosamine at site C. Good electron density for the trisaccharide in the PEWL complex structure shows that Asp 101 is involved in hydrogen bonding interactions with the terminal sugar residue.
Animals↗
Urokinase plasminogen activator expression by primary and HPV 16-transformed keratinocytes.
The molecular events underlying progression of human papillomavirus (HPV) 16-associated intraepithelial neoplasia to invasive cancer have not been studied in detail. Penetration of the basement membrane is an early, but poorly understood step in this process and probably involves the action of one or more metallo- and serine proteinases. Urokinase-type plasminogen activator (uPA) is a serine proteinase that has been implicated in the pathogenesis of several epithelial tumors, but its role in HPV-associated tumors is not known. To examine uPA expression by HPV 16-transformed keratinocytes in vitro, primary foreskin keratinocyte cultures were transfected by HPV 16 DNA. The primary parental cells and the HPV 16-transformed keratinocytes were studied using substrate gel zymography, Western blot analysis and an in vitro assay measuring penetration of a Matrigel artificial basement membrane. Both uPA and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), were overexpressed in the HPV 16-transformed cells relative to the parental cell line. The transformed cells, but not the parental cells, were able to degrade and penetrate the Matrigel membrane and penetration was blocked by both PAI-1 and by antibodies to uPA. Our data suggest that HPV 16-induced transformation of keratinocytes is associated with upregulation of uPA expression. In conjunction with other proteinases, uPA plays an important role in the ability of HPV 16-transformed keratinocytes to penetrate artificial basement membranes.
Basement Membrane↗
Combined spinal epidural anaesthesia: the single space double-barrel technique.
We present our own single-space method for performing combined spinal epidural anaesthesia. A spinal introducer and a Tuohy needle are sited in the same interspace. After insertion of the epidural catheter the introducer is used as a guide for a 25 gauge spinal needle. The advantages of this technique over other methods are explored. A series of 90 patients who received combined spinal epidural anaesthesia for elective Caesarean section is presented. The incidence of side effects (hypotension, nausea and vomiting, itching, post dural puncture headache) was comparable with those of other series. However, a high incidence (26.6%) of paraesthesiae during insertion of the spinal needle was noted. We suggest that this finding may be related to the use of pencil-point needles.
Journal Article↗
Congenital abnormalities of the pancreas and biliary tree in adults.
Congenital abnormalities of the pancreaticobiliary tree may go undetected until adulthood. In adult patients with persistent and unexplained signs and symptoms, such as cholangitis, pancreatitis, jaundice, recurrent abdominal pain, and nausea and vomiting, a congenital anomaly of the pancreatic or bile duct must be considered and a low threshold for performing cholangiopancreatography is recommended. The most common congenital pancreaticobiliary abnormalities seen in adults are choledochal cyst, anomalous junction of the pancreatic and common bile ducts, aberrant biliary ducts, and pancreas divisum, with the following entities being more rarely seen: choledochoceles, multiple communicating intra- and extrahepatic duct cysts, Caroli disease, pancreaticobiliary abnormalities associated with situs anomalies, annular pancreas, and aberrant pancreatic ducts associated with enteric duplication cysts. Cholangiopancreatography allows confirmation of diagnosis and may demonstrate associated abnormalities such as choledocholithiasis or tumor. Recognition of congenital anomalies may aid in surgical planning and prevent inadvertent ductal injury. Although congenital pancreaticobiliary abnormalities are relatively uncommon, the increased prevalence of cholangitis, gallstones, and cholangiocarcinoma seen with the various types of biliary cystic disease and junctional anomalies and the increased association of pancreatitis seen with pancreatic anomalies make recognition of variant anatomy clinically important.
Adult↗
Benign bronchial stenosis treated with balloon bronchoplasty and metal stents.
We report a case of a benign bronchial stenosis that presented clinically with recurrent respiratory infections and increasing dyspnoea. This was associated with transradiancy and oligaemia of the ipsilateral lung. Treatment with balloon bronchoplasty and self-expanding metal stents prevented recurrent pneumonia and led to a sustained improvement in exercise tolerance.
Aged↗
Cardiac hypertrophy impairs recovery from ischaemia because there is a reduced reactive hyperaemic response.
OBJECTIVE: The aim was to investigate whether impaired coronary flow reserve associated with cardiac hypertrophy could significantly limit the flow debt repayment following short periods of coronary occlusion and exacerbate or prolong episodes of myocardial ischaemia. METHODS: Left ventricular hypertrophy was induced in guinea pigs by aortic constriction and the hearts were isolated six weeks later for Langendorff perfusion. Sham operated animals served as controls. The reactive hyperaemic response was studied following various lengths of occlusion of flow and the extent of aerobic and anaerobic metabolism was assessed in each group. RESULTS: Heart weight/body weight ratio was increased by approximately 25% (P < 0.001) with aortic constriction. The reactive hyperaemic flow response in isolated hearts was impaired by hypertrophy in both magnitude (P < 0.05) and duration. The repayment of flow debt was also significantly reduced, suggesting an inadequate recovery of the myocardium following the occlusion. The total amount of O2 consumed by the heart throughout the duration of hyperaemia was less in hypertrophy than in sham operated controls, suggesting a decrease in aerobic metabolism. Total lactate discharge expressed as a ratio of O2 consumed, which provides an estimation of the degree of anaerobic in relation to aerobic metabolism, was greater in hypertrophy than in sham operated controls. CONCLUSIONS: The hypertrophied heart is more vulnerable to brief periods of ischaemia because of an impaired reactive hyperaemic response which results in delayed metabolic recovery. These abnormalities may contribute to the increased morbidity associated with cardiac hypertrophy.
Animals↗
Crystallization and preliminary X-ray analysis of a mutant duck delta II crystallin.
A duck delta II crystallin mutant, where histidine 178 has been replaced by an aspartic acid residue, has been purified from a bacterial expression system and subsequently crystallized. The crystals grow as flat plates, with unit cell dimensions a = 94.1 A, b = 99.9 A, c = 108.7 A and beta = 102 degrees. The crystals exhibit the symmetry of space group P2(1) and diffract to a minimum d-spacing of 2.8 A resolution. On the basis of density calculation four monomers (one tetramer) are estimated to be present in the asymmetric unit (Vm = 2.5 A3/Da). Self-rotation functions clearly show the presence of 222 non-crystallographic symmetry.
Animals↗