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PubMed2003

Prophage insertion sites.

Insertion of viral DNA into host chromosomes is an ancient process essential for propagation in the proviral form. Many present-day bacteriophages insert at specific sites on the host chromosome. Insertion by two coliphage families (lambdoid and P4-like) is compared. For both families, insertion sites frequently lie within tRNA genes. The lambdoid phages insert at anticodon loops, whereas the p4-like phages insert in the TpsiC loops downstream from them. The association of both groups with tRNA genes suggests that the primordial insertion site of both groups may have been within a tRNA gene. The integrase proteins used in phage insertion may have originated at that stage, with subsequent diversification of specificity.

Attachment Sites, Microbiological↗

PubMed2001

Bedside insertion of inferior vena cava filters in the intensive care unit.

BACKGROUND: Several authors have showed that bedside insertion of inferior vena cava filters (IVCF) is feasible and cost effective, with the additional benefit of not having to transport a critically ill patient to the operating room or radiology department. The objective of this study was to examine our experience of 158 IVCF insertions at the bedside in the intensive care unit. STUDY DESIGN: A prospective, observational study of bedside IVCF insertion performed by the authors from February 1996 through August 2000 was undertaken. RESULTS: One hundred fifty-eight patients underwent bedside IVCF insertion in the intensive care unit. The mean age was 42.2 years (SD 17.5 years). The mean Injury Severity Score of the trauma patients was 27.3 (SD 14.5). The majority of patients (90%) had a prophylactic indication for IVCF insertion using our institutional guidelines for venous thromboembolic prophylaxis for trauma patients. All IVCF insertions were successfully performed at the bedside after iodinated contrast or carbon dioxide cavography. The mortality was 11% (n = 18), none attributable to the IVCF insertion or cavagram. There was one asymptomatic cava occlusion and one postinsertion pulmonary embolus in a patients with a subclavian vein thrombosis. CONCLUSIONS: Our results demonstrate the safety and efficacy of IVCF insertion at the bedside in the ICU. This method offers less resource use and more safety for critically ill patients, avoiding the hazards of intrahospital transport.

Adult↗

PubMed2004

Unusual codon 69 insertions: influence on human immunodeficiency virus type 1 reverse transcriptase drug susceptibility.

INTRODUCTION: Multiple amino acid changes in the reverse transcriptase (RT) enzyme of the human immunodeficiency virus 1 (HIV-1) confer simultaneous resistance to most nucleoside RT inhibitors (NRTI). It may take place through different pathways: one of these is the codon 69 insertion, which can involve several 2-amino acid patterns. MATERIALS AND METHODS: We are reporting the case of three patients treated with various antiretroviral compounds. For these subjects we have conducted both a genotypical and a phenotypical analysis in order to understand what kind of influence these insertions may have on HIV-1 RT drug susceptibility. Plasma samples from these patients have been extracted and the RT region has been amplified, cloned and sequenced; meanwhile their PBMCs have been separated, cultivated and then tested for drug susceptibility. RESULTS: Data obtained from the cloning assay showed that the patients had different mutational patterns but constant multiple resistance to NRTI. In particular, they harbored mutations related to Zidovudine (ZDV), 3TC and various NRTIs. Moreover, all three samples had a T69S substitution followed by three different dual amino acid insertions: SG, TG and VG. Several phenotypic experiments revealed that the viruses were resistant to 3TC as well as to ZDV and ABC. Different results were obtained using d4T and ddI. DISCUSSION: In our three patients, all mutation inserts impaired the use of NRTI, particularly ZDV and 3TC. Patient 001 presented a pattern that should not cause a high phenotypic resistance to 3TC per se, and so we can argue that the concomitant presence of the insertion T69S (SG) makes this isolate moderately resistant to this drug. We observed a similar phenomenon in subject 003. d4T was less involved in the resistance generation caused by the RT insertion (in one out of three cases). Moreover, we identified a new 2aa insertion (TG) that has, to the best of our knowledge, never been reported before. A careful survey of novel RT genotypic insertion is thus warranted.

Amino Acid Substitution↗

PubMed1993

Influence of 5'-nearest neighbors on the insertion kinetics of the fluorescent nucleotide analog 2-aminopurine by Klenow fragment.

The effects of nearest neighbor interactions between a nucleotide base at the primer 3'-terminus and an incoming deoxyribonucleoside triphosphate on DNA polymerase catalyzed insertion were examined. Kinetics of inserting the fluorescent nucleotide analog 2-aminopurine deoxyribonucleotide (dAPMP) and dAMP opposite a template T by 3'-->5' exonuclease-deficient mutants of Klenow fragment (KF-) were measured on primer/templates of identical sequence except for the base pair at the 3'-primer terminus. In addition to its fluorescence properties, 2-aminopurine (AP) is an attractive probe because it is misinserted opposite T by polymerases at much higher frequencies than natural nucleotides. Misinsertion frequencies for AP are on the same order of magnitude as variations in misinsertion frequencies due to changes in local DNA sequence, which makes the statistical significance of these variations easier to document. We have established that changes in the fluorescence of AP can be used to follow the insertion of dAPMP on both steady-state and pre-steady-state time scales. Rates of insertion of dAPMP measured by fluorescence and by a polyacrylamide gel assay were similar and are sensitive to the identity of the base at the 3'-primer twice as fast as insertion following a primer terminus T. The difference in rates arises primarily from differences in kcat values, which were fastest next to G and slowest next to T, while apparent Km values were similar next to each of the 4 different nearest neighbors. The gel assay was used to measure AP misinsertion efficiencies by two methods: (1) by having dAPTP and dATP directly compete for insertion opposite T in the same reaction and (2) by measuring Vmax/Km values for each substrate in separate reactions. The results from the direct competition and separate kinetics measurements are similar. The misinsertion efficiency of dAPMP relative to dAMP opposite a template T was significantly higher next to a 3'-primer terminus G (f(ins) = 0.31 +/- 0.06) than next to T (f(ins) = 0.15 +/- 0.03) for the KF- single mutant (D42A). The corresponding misinsertion efficiencies next to a 3'-primer terminus G and T were 0.20 +/- 0.02 and 0.16, respectively, for the KF- double mutant (D355A, E357A). Relative rates of insertion of dAPMP and dAMP correlate with melting temperatures calculated for nearest neighbor doublets which reflect the relative base-stacking energies. In addition to changes in insertion kinetics, polymerase-DNA dissociation rates varied with the identity of the 3'-primer terminus, differing by as much as 7-20-fold depending on the polymerase and the primer/template.

2-Aminopurine↗

PubMed2001

Effect of nonbilayer lipids on membrane binding and insertion of the catalytic domain of leader peptidase.

Biological membranes contain a substantial amount of "nonbilayer lipids", which have a tendency to form nonlamellar phases. In this study the hypothesis was tested that the presence of nonbilayer lipids in a membrane, due to their overall small headgroup, results in a lower packing density in the headgroup region, which might facilitate the interfacial insertion of proteins. Using the catalytic domain of leader peptidase (delta2-75) from Escherichia coli as a model protein, we studied the lipid class dependence of its insertion and binding. In both lipid monolayers and vesicles, the membrane binding of (catalytically active) delta2-75 was much higher for the nonbilayer lipid DOPE compared to the bilayer lipid DOPC. For the nonbilayer lipids DOG and MGDG a similar effect was observed as for DOPE, strongly suggesting that no specific interactions are involved but that the small headgroups create hydrophobic interfacial insertion sites. On the basis of the results of the monolayer experiments, calculations were performed to estimate the space between the lipid headgroups accessible to the protein. We estimate a maximal size of the insertion sites of 15 +/- 7 A2/lipid molecule for DOPE, relative to DOPC. The size of the insertion sites decreases with an increase in headgroup size. These results show that nonbilayer lipids stimulate the membrane insertion of delta2-75 and support the idea that such lipids create insertion sites by reducing the packing density at the membrane-water interface. It is suggested that PE in the bacterial membrane facilitates membrane insertion of the catalytic domain of leader peptidase, allowing the protein to reach the cleavage site in preproteins.

Catalytic Domain↗

PubMed2006

Isoform-specific membrane insertion of secretory phospholipase A2 and functional implications.

Despite increasing evidence that the membrane-binding mode of interfacial enzymes including the depth of membrane insertion is crucial for their function, the membrane insertion of phospholipase A(2) (PLA(2)) enzymes has not been studied systematically. Here, we analyze the membrane insertion of human group IB PLA(2) (hIBPLA(2)) and compare it with that of a structurally homologous V3W mutant of human group IIA PLA(2) (V3W-hIIAPLA(2)) and with a structurally divergent group III bee venom PLA(2) (bvPLA(2)). Increasing the anionic charge of membranes results in a blue shift of the fluorescence of Trp(3) of hIBPLA(2), a decrease in quenching by acrylamide, and an increase in enzyme activity, reflecting an enhancement in the membrane binding of PLA(2). Fluorescence quenching by brominated lipids indicates significant penetration of Trp(3) into fluid POPC/POPG membranes but little insertion into the solid DPPC/DPPG membranes. Increased membrane fluidity also supports hIBPLA(2) activity, suggesting that membrane insertion of hIBPLA(2) is controlled by membrane fluidity and is necessary for the full activity of the enzyme. Trp fluorescence quenching of the V3W-hIIAPLA(2) and bvPLA(2) by water- and membrane-soluble quenchers indicates substantial membrane insertion of Trp(3) of V3W-hIIAPLA(2), similar to that found for hIBPLA(2), and no insertion of tryptophans of bvPLA(2). Our results provide evidence that (a) structurally similar group IB and IIA PLA(2)s, but not structurally diverse group III PLA(2), significantly penetrate into membranes; (b) membrane insertion is controlled by membrane fluidity and facilitates activation of IB and IIA PLA(2)s; and (c) structurally distinct PLA(2) isoforms may employ different tactics of substrate accession/product release during lipid hydrolysis.

Animals↗

PubMed1996

Thermodynamics of the membrane insertion process of the M13 procoat protein, a lipid bilayer traversing protein containing a leader sequence.

For the first time, the standard free energy change, delta Gzero, of a membrane-inserting protein with a leader sequence has been determined experimentally, using M13 procoat protein as an example. The partition coefficient for the distribution of the procoat protein between the aqueous phase and the membrane phase of preformed lipid vesicles yielded a value of gamma = 6.5 x 10(5) M-1, corresponding to a delta Gzero of -10.4 kcal/mol, based on measurements of the fluorescence energy transfer between the intrinsic tryptophan of the protein and a suitably labeled lipid membrane of POPC. For comparison, the partition coefficient of the M13 coat protein between the aqueous and the POPC lipid bilayer phase was determined to be distinctly lower: gamma = 1 x 10(5) M-1 (delta Gzero = -9.3 kcal/mol). Proteinase K digestion experiments have been performed, showing that 20% of the procoat protein bound to lipid vesicles spontaneously integrate in a transbilayer form, whereas 80% remain inserted in the interfacial membrane region. By taking together these results, an upper limit for the free energy change of the transmembrane insertion of procoat protein was estimated to be -14.8 kcal/mol. In order to distinguish further the contribution arising from insertion of the procoat protein into the membrane interfacial region from that due to transmembrane insertion, the partition coefficient of the mutant procoat protein OM30R [which contains a positively charged amino acid in its mature hydrophobic segment (exchange of a Val to an Arg residue at position 30)] was determined, yielding gamma = 0.3 x 10(5) M-1 (delta Gzero = -8.6 kcal/mol). Previously reported in vivo experiments have shown that the OM30R mutant protein is not translocated across Escherichia coli membranes but only binds to the inner surface. The results presented here indicate that although the insertion of the procoat protein into the interfacial region of the lipid bilayer contributes the major part to delta Gzero, it is the final energy gain of the interaction of the hydrophobic portions of the folded pre-protein with the lipid chains which drives the transmembrane insertion of the M13 procoat protein. Neither the leader sequence nor the mature coat protein alone yields this free energy gain. For the different proteins investigated here, spontaneous membrane insertion occurs only for fluid lipid bilayers, but not for membranes in the crystalline lipid phase. Furthermore, by using lipid bilayers with negative membrane surface charges, it was shown that both procoat and coat proteins are electrostatically attracted to the surface of the lipid membrane, though only to a small extent, with apparent partition coefficients of the same order of magnitude as for the phosphatidylcholine lipid membrane.

Amino Acid Sequence↗

PubMed1996

Folding intermediates of a beta-barrel membrane protein. Kinetic evidence for a multi-step membrane insertion mechanism.

The mechanism of folding and membrane insertion of integral membrane proteins, including helix bundle and beta-barrel proteins is not well understood. A key question is whether folding and insertion are coupled or separable processes. We have used the beta-barrel outer membrane protein A (OmpA) of Escherichia coli as a model to study the kinetics of folding and insertion into dioleoylphosphatidylcholine (DOPC) bilayers, as a function of temperature by gel electrophoresis, protease digestion, and fluorescence spectroscopy. OmpA was unfolded in 8 M urea solution (without detergent), and refolding and membrane insertion was initiated by rapid dilution of the urea concentration in the presence of phospholipid vesicles. In addition to the kinetically unresolved hydrophobic collapse in water, the time course of refolding of OmpA into DOPC bilayers exhibited three kinetic phases over a large temperature range. The first step was fast (k1 = 0.16 min-1) and not very dependent on temperature. The second step was up to two orders of magnitude slower at low temperatures (2 degrees C), but approached the rate of the first step at higher temperatures (40 degrees C). The activation energy for this process was 46 +/- 4 kJ/mol. A third slow process (k3 = 0.9 x 10(-2) min-1 at 40 degrees C) was observed at the higher temperatures. These results suggest that at least two membrane-bound intermediates exist when OmpA folds and inserts into lipid bilayers. We also show that both membrane-bound intermediates can be stabilized in fluid lipid bilayers at low temperatures. These intermediates share many properties with the adsorbed/partially inserted form of OmpA that was previously characterized in gel phase lipid bilayers [Rodionova et al. (1995) Biochemistry 34, 1921-1929]. Temperature jump experiments demonstrate, that the low-temperature intermediates can be rapidly converted to fully inserted native OmpA. On the basis of these and previous results, we present a simple folding model for beta-barrel membrane proteins, in which folding and membrane insertion are coupled processes which involve at least four kinetically distinguishable steps.

Bacterial Outer Membrane Proteins↗

PubMed1997

Use of Trp mutations to evaluate the conformational behavior and membrane insertion of A and B chains in whole diphtheria toxin.

The structure of diphtheria toxin was examined using its Trp fluorescence. To examine the interactions of the A and B chains of the toxin independently, mutants were constructed in which Trp residues were restricted to either the A or the B chain. The conformation and stability of the mutants were very similar to those of the wild-type protein. In addition, they underwent the low-pH conformational transition and membrane insertion at about the same pH as wild-type toxin. This shows Trp do not play a critical role in these processes which are necessary for the translocation of toxin across endosomal membranes in vivo. There was a shift in fluorescence of the Trp mutants which showed the low-pH-induced transition increases exposure of both the A and B Trp to a more polar environment. This supports a model in which the interdomain interactions present at neutral pH break down at low pH. To evaluate the location of the A and B chains in the membrane, the fluorescence quenching of model membrane inserted toxin was measured. Comparison of the amount of quenching by lipid labeled with nitroxides localized at shallow, medium, or deep depths within the bilayer demonstrated that both the A and B chains insert deeply, but the A chain Trp are somewhat less deeply inserted. Trp on the A chain are also less exposed to lipid than on the B chain, as judged by their weaker quenching by the nitroxide-labeled lipid. This conclusion was supported by the observation that the Trp of membrane-inserted isolated A chain is more lipid-exposed than when the A chain is part of the whole toxin. Both the A and B chain Trp become less exposed to lipid after neutralizing pH. However, both chains remain inserted, with at least part of the B chain remaining deeply inserted. These results support the "partial wrapper" model in which both the A and B chains are inserted but contacts between the two chains significantly reduce the exposure of the A chain to lipid.

Diphtheria Toxin↗

PubMed2005

Hydrogenated 1,4-insertion of butadiene in the copolymerization with propylene using an isospecific zirconocene catalyst.

Poly(propylene-ran-1,3-butadiene) that contained pendant vinyl groups derived from 1,2-inserted butadiene units was selectively synthesized by rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride (Ph-Ind) activated with modified methylaluminoxane (MMAO) in the presence of hydrogen. The copolymers obtained without hydrogen had 1,2-inserted and 1,4-inserted butadiene units. The addition of hydrogen to the copolymerization improved the activity by approximately 1000-fold and gave the copolymer only with 1,2-inserted butadiene units, of which the content was equal to the copolymer obtained without hydrogen. The 13C NMR analysis of the copolymers clarified that butadiene also inserted into the copolymer as a tetramethylene unit, of which the content was almost the same as that of 1,4-inserted butadiene units observed in the absence of hydrogen. No signal that could be assigned to cyclic structures or long branched side chains was observed. These results indicate that pi-allyl species of zirconocenes formed by 1,4-butadiene insertion at the growing polymer chain ends transformed to the tetramethylene chain end by hydrogenation and continued successive propylene insertion.

Journal Article↗

PubMed1997

An insert in the motor domain determines the functional properties of expressed smooth muscle myosin isoforms.

Smooth muscle myosin isoforms of the heavy chain and the essential light chain have been hypothesized to contribute to the different shortening velocities of phasic and tonic smooth muscles, and to their different affinities for MgADP. We used the baculovirus/insect cell system to express homogeneous heavy meromyosin molecules differing only in seven amino acid insert (QGPSFSY) in the motor domain near the active site, or in the type of essential light chain isoform. Myosin from tonic rabbit uterine smooth muscle lacks the heavy chain insert, while myosin from phasic chicken gizzard contains it. The properties of a mutant uterine heavy meromyosin with added insert, and a mutant gizzard heavy meromyosin with the insert deleted, were compared with their wild type progenitors. Phosphorylated heavy meromyosins with the insert have a twofold higher enzymatic activity and in vitro motility han heavy meromyosins without the insert. These functional properties were not altered by the essential light chain isoforms. The altered motility caused by the insert implies that it modulates the rate of ADP release, the molecular step believed to limit shortening velocity. The insert may thus account in part for both the lower sensitivity to MgADP and the higher shortening velocity of phasic compared to tonic smooth muscles.

Actins↗

PubMed1998

Thrombin specificity: further evidence for the importance of the beta-insertion loop and Trp96. Implications of the hydrophobic interaction between Trp96 and Pro60B Pro60C for the activity of thrombin.

A number of thrombin mutants have been constructed to investigate the role of Trp96 and the beta-insertion loop for the specificity of thrombin. Thrombin(60D) consists of the replacement of the beta-insertion loop (14 amino acid residues from 59 to 63, including a 9-residue insertion at position 60) with the corresponding four residues in trypsin, Tyr-Lys-Ser-Gly; thrombin(GGG) is a smaller loop mutation in which the residues Tyr(60A)Pro(60B)Pro(60C)Trp(60D) Asp(60E)Lys(60F) of the beta-insertion loop were replaced by Gly-Gly-Gly; thrombin(96S) consists of a point mutation Trp96 --> Ser; and thrombin(GGG/96S) is the double mutant incorporating both changes. Thrombin(96S) clots fibrinogen approximately 3 times more slowly than thrombin, with the two beta-insertion loop mutants, thrombin(GGG) and thrombin(GGG/96S), reacting approximately 3000- and 1300-fold more slowly, respectively. The specificity constant kcat/Km for the cleavage of fibrinopeptide A and fibrinopeptide B by thrombin(96S) was 2.6 and 0.35 microM(-1) s(-1), respectively, compared to 10 and 2.5 microM(-1) s(-1) for wild-type recombinant thrombin, respectively. Kinetic constants were determined for the hydrolysis of H-D-phenylalanyl-L-pipecolyl-L-arginine-p-nitroaniline. The Michaelis constant Km increased approximately 6-fold for thrombin(96S) and >200-fold for thrombin(GGG) and thrombin(GGG/96S) when compared to wild-type recombinant thrombin, while the catalytic constant kcat remained approximately the same. All mutants were more susceptible to inhibition by BPTI than wild-type recombinant thrombin. Clearly, the beta-insertion loop is important for thrombin activity. But the mutation of Trp96 --> Ser can compensate somewhat for the loss of binding at the beta-insertion loop. The deletion of the hydrophobic interaction between Trp96 and Pro(60B)Pro(60C) appears to decrease the stability of the beta-insertion loop, thereby causing a decrease in binding efficiency.

Fibrinogen↗

PubMed1999

Comparison of periodontal pocket penetration by conventional and microultrasonic inserts.

Recently, 'microultrasonic' instruments have been developed with the aim of improving root-surface debridement. Whilst their reduced tip diameter and modified shape suggests that they may penetrate the periodontal pocket more easily than conventional inserts, there have been few studies investigating their efficacy. The aim of this investigation was therefore to compare the periodontal pocket penetration of a conventional ultrasonic insert (P10 insert--Dentsply) with microultrasonic inserts (Slimline FSI left and right--Dentsply). Efficacy of penetration was assessed by a modification of instrument limit. This modification permitted measurement of the linear % removal of the apical plaque border by image analysis. Debridement was carried out on randomly allocated surfaces of 30 teeth which had been treatment planned for extraction due to periodontitis. One surface on each tooth acted as an untreated control. The results of this study showed that both types of insert were able to reach and debride the apical plaque border, and at all pocket depths assessed. However no significant differences were found between the Slimline insert and the P10 tip. Trends between instruments were observed which suggest that the Slimline insert might more easily penetrate to and debride the apical plaque border in deep pockets, whereas the P10 insert might be more effective in disrupting the apical plaque border in shallow pockets. Future investigations using a larger sample size will be needed to confirm these observations.

Analysis of Variance↗

PubMed2006

Distinct modes of regulated receptor insertion to the somatodendritic plasma membrane.

Many neural signaling receptors are regulated by endocytosis, but little is known about receptor insertion into the plasma membrane. Time-lapse imaging of the beta2 adrenergic receptor expressed in cultured rat hippocampal neurons, using pH-sensitive green fluorescent protein tagging and total internal reflection fluorescence microscopy, resolved distinct vesicular fusion events mediating receptor insertion into the somatodendritic plasma membrane. A 'transient' insertion mode resulted in rapid lateral dispersion of receptors immediately after insertion. A 'persistent' insertion mode resulted in the retention of inserted receptors in surface-accessible domains, which were relatively immobile for a prolonged 'wait' period before dispersing laterally. Distinct insertion modes were oppositely regulated by receptor activation and by mechanisms differing in their dependence on the signaling effector cyclic AMP-dependent protein kinase. These results reveal a new mechanism for homeostatic regulation of postsynaptic signaling and a 'kiss-and-wait' mode of regulated membrane protein insertion in neurons.

Adrenergic beta-Agonists↗

PubMedDate not supplied

Comparison of insertion time and pullout strength between self-tapping and non-self-tapping AO 4.5-mm cortical bone screws in adult equine third metacarpal bone.

OBJECTIVE: To compare screw insertion characteristics and pullout mechanical properties between self-tapping (ST) and non-self-tapping (NST) AO 4.5-mm cortical bone screws in adult equine third metacarpal bone (MC3). STUDY DESIGN: In vitro biomechanical experiment. ANIMALS OR SAMPLE POPULATION: Seven pairs of adult equine MC3. METHODS: Bicortical holes were drilled transversely in proximal metaphyseal, diaphyseal, and distal metaphyseal locations of paired MC3. NST screws were inserted in pre-tapped holes in 3 sites of one bone pair, and ST screws were inserted in non-tapped holes of contralateral MC3. Tapping and screw insertion times and maximum torques were measured. Screw pullout mechanical properties were determined. RESULTS: Screw insertion time was longer for ST screws. Total time for tapping and insertion (total insertion time) was over twice as long for NST screws. Statistically significant differences were not observed between screws for any pullout mechanical property. From pullout tests, diaphyseal locations had significantly stiffer and stronger structure than metaphyseal locations. Pullout failure more commonly occurred because of screw breakage than bone failure. Bone failure and bone comminution were more commonly associated with ST screws. Bone failure sites had pullout failure loads that were 90% of screw failure sites. CONCLUSIONS: NST and ST 4.5-mm-diameter cortical bone screws have similar pullout mechanical properties from adult equine MC3. ST screws require less than half the total insertion time of NST screws. CLINICAL RELEVANCE: Use of ST 4.5-mm-diameter cortical bone screws should be considered for repair of adult equine MC3 fractures; however, bone failures at screw sites should be monitored.

Animals↗

PubMed1986

[Pathological insertion of the placenta after the 20th week of pregnancy--its importance in the course of pregnancy and delivery].

The present paper reports on the results of sonographic diagnosis of a pathologic insertion of the placenta after the 20th week of pregnancy and its importance with regard to the course of pregnancy and birth. The conversion of a primarily pathologic placental insertion to a "normal" insertion at term depends on the severity of the placental insertion disorder and the date of diagnosis. The frequency of pathologic insertions after the 20th week of pregnancy amounted to 4.2% of the patients examined. The rate of conversion from pathologic to normal placental insertion was 91%, if marginal/partial and total placenta previa are accepted as definitive diagnoses at term. The insertion remained unchanged up to term in approximately 90% of the cases in which total placenta previa was sonographically diagnosed. The sonographic diagnosis of "pathologic insertion of the placenta" after the 20th week of pregnancy is associated with severe complications in the subsequent course of pregnancy and birth. There is a significant cluster of vaginal hemorrhage in the last trimester of pregnancy; cesarean deliveries are common; there are more cases of transfer to pediatric clinics, and the incidence of retarded fetal growth and perinatal mortality is higher. The present authors believe that where the diagnosis of placenta previa has been confirmed sonographically, prophylactic measures and, in the last resort, a planned cesarean delivery can contribute to a reduction in maternal morbidity and also to a decrease in perinatal morbidity and mortality.

Abortion, Spontaneous↗

PubMed1986

[Distance of muscle insertions in the corneal limbus].

During the last 3 years (1983 to 1985) accurate measurements of the distance between rectus muscle insertions and the corneal limbus were made on strabismus patients during surgery. After dissection of a muscle the distance from the posterior limbus (gray-white line) to the insertion line of the muscle was measured with calipers both at the midpoint and at each end of the insertion. A limbal incision was employed without exception. Statistical analysis was performed on a personal computer, using the Lotus 1-2-3 program. In contrast to the traditionally popular values determined by Fuchs, which are already over 100 years old (in parentheses), we found the following mean values: medial rectus insertion 4.5 mm (5.5), in 675 eyes operated on; inferior rectus insertion 5.67 mm (6.5), in 22 eyes operated on; lateral rectus insertion 6.20 mm (6.9), in 493 eyes operated on; and superior rectus insertion 6.64 (7.7), in 21 eyes operated on. The reasons for these differences are discussed. Because of the large size of the samples for the horizontal muscles it was possible to narrow down the confidence limits for the true mean values considerably; however, it is clear from the great differences between the lowest and highest values observed that the distance from the muscle insertions to the corneal limbus varies widely.

Adolescent↗

PubMed2005

Rare-gas insertion compounds of perfluorobenzene: aromaticity of some unstable species.

Calculations on the novel argon insertion compounds C6F6Ar(n), n = 1-6, where the argon atoms are inserted into the C-F bonds in perfluorobenzene, suggest that all possible species, with one to six inserted argon atoms, occupy minima on their respective potential energy surfaces. Ring-current plots using the ipsocentric model indicate that there is no disruption of the aromatic pi system upon argon insertion, and consequently all insertion compounds are aromatic according to the magnetic criterion. The barrier height for decomposition of the single-insertion compound, C6F6Ar, into C6F6+Ar is 19.5 kcal/mol at HF6-311G** and 29.5 kcal/mol at B3LYP6-311G**, suggesting that, although clearly thermodynamically unstable, argon-perfluorobenzene insertion compounds may be stable kinetically. Preliminary calculations indicate that other rare gas-perfluorobenzene insertion compounds may also be metastable. Both C6F6Ne and C6F6He are predicted to occupy minima on their respective potential energy surfaces.

Journal Article↗