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At least 1,153 records · Page 64Linked to original sources
PubMed2000

Structural basis for nucleotide exchange and competition with tRNA in the yeast elongation factor complex eEF1A:eEF1Balpha.

The crystal structure of a complex between the protein biosynthesis elongation factor eEF1A (formerly EF-1alpha) and the catalytic C terminus of its exchange factor, eEF1Balpha (formerly EF-1beta), was determined to 1.67 A resolution. One end of the nucleotide exchange factor is buried between the switch 1 and 2 regions of eEF1A and destroys the binding site for the Mg(2+) ion associated with the nucleotide. The second end of eEF1Balpha interacts with domain 2 of eEF1A in the region hypothesized to be involved in the binding of the CCA-aminoacyl end of the tRNA. The competition between eEF1Balpha and aminoacylated tRNA may be a central element in channeling the reactants in eukaryotic protein synthesis. The recognition of eEF1A by eEF1Balpha is very different from that observed in the prokaryotic EF-Tu:EF-Ts complex. Recognition of the switch 2 region in nucleotide exchange is, however, common to the elongation factor complexes and those of Ras:Sos and Arf1:Sec7.

Binding Sites↗
PubMed2000

Structure of the AAA ATPase p97.

p97, an abundant hexameric ATPase of the AAA family, is involved in homotypic membrane fusion. It is thought to disassemble SNARE complexes formed during the process of membrane fusion. Here, we report two structures: a crystal structure of the N-terminal and D1 ATPase domains of murine p97 at 2.9 A resolution, and a cryoelectron microscopy structure of full-length rat p97 at 18 A resolution. Together, these structures show that the D1 and D2 hexamers pack in a tail-to-tail arrangement, and that the N domain is flexible. A comparison with NSF D2 (ATP complex) reveals possible conformational changes induced by ATP hydrolysis. Given the D1 and D2 packing arrangement, we propose a ratchet mechanism for p97 during its ATP hydrolysis cycle.

Adenosine Diphosphate↗
PubMed1999

The length of the flexible SNAREpin juxtamembrane region is a critical determinant of SNARE-dependent fusion.

The topology of a SNARE complex bridging two docked vesicles could act as a mechanical couple to do work on the lipid bilayer resulting in fusion. To test this, we prepared a series of modified SNARE proteins and determined their effects on SNARE-dependent membrane fusion. When two helix-breaking proline residues are introduced into the juxtamembrane region of VAMP, there is little or no effect on fusion, and the same change in syntaxin 1A only reduced the extent and rate of fusion by half. The insertion of a flexible linker between the transmembrane domain and the conserved coiled-coil domain only moderately affected fusion; however, fusion efficiency systematically decreased with increasing length of the linker. Together, these results rule out a requirement for helical continuity and suggest that distance is a critical factor for membrane fusion.

Amino Acid Sequence↗
PubMed1999

Functional organization of clathrin in coats: combining electron cryomicroscopy and X-ray crystallography.

The sorting of specific proteins into clathrin-coated pits and the mechanics of membrane invagination are determined by assembly of the clathrin lattice. Recent structures of a six-fold barrel clathrin coat at 21 A resolution by electron cryomicroscopy and of the clathrin terminal domain and linker at 2.6 A by X-ray crystallography together show how domains of clathrin interact and orient within the coat and reveal the strongly puckered shape and conformational variability of individual triskelions. The beta propeller of the terminal domain faces the membrane so that recognition segments from adaptor proteins can extend along its lateral grooves. Clathrin legs adapt to different coat environments in the barrel by flexing along a segment at the knee that is free of contacts with other molecules.

Clathrin↗
PubMed2003

Relationship between cranio-cervical flexion range of motion and pressure change during the cranio-cervical flexion test.

The purpose of this study was to quantify the sagittal angular displacement of the head (cranio-cervical flexion) for the five incremental stages of the cranio-cervical flexion test (CCFT). Range of cranio-cervical flexion during the CCFT was measured using a digital imaging method in 20 healthy volunteer subjects. The intra-and inter-rater reliability of the digital imaging technique for the assessment of this movement were also examined. The results of this study demonstrated a linear relationship between the incremental pressure targets of the CCFT and the percentages of full range cranio-cervical flexion range of motion (ROM) measured in the supine lying position of the test using a digital imaging technique. A mean of 22.9% full range cranio-cervical flexion was used to reach the first pressure target of the CCFT followed by linear increments up to 76.6% for the last stage of the test. An increasing amount of cranio-cervical flexion ROM was used to achieve the five successive stages of the CCFT reflecting an increasing contractile demand on the deep cervical flexor muscles. Excellent inter-rater (ICC=0.994) and intra-rater reliability (ICC=0.988-0.998) were demonstrated for the angular measurements using this digital imaging technique.

Adult↗
PubMed2001

Physiological profiles of Australian surf boat rowers.

The physiological profiles of 17 open grade (OG) and 13 reserve grade (RG) male surfboat rowers (SBR) aged 19-44 years were determined and compared. Parameters investigated included anthropometry, agility, isometric strength, flexibility, rowing ergometer performance (MT), peak VO2 and arterialised blood pH, lactate and bicarbonate. Means were compared using t-tests. Multiple regression analyses provided a number of models for the prediction of MT performance in SBR. The mean age, height, mass, and sum of eight skinfolds for SBR are: 26.2 (+/-5.9) years, 180.5 (+/-6.0) cm, 84.4 (+/-9.3) kg and 78.2 (+/-26.2) mm respectively. OG rowers were significantly different from RG for the parameters of ergometer performance (OG: 1360.2+/-42.9 m; RG: 1316.4+/-41.8 m), peak ventilation (OG: 174.2+/-17.2 L x min(-1); RG: 154.8+/-22.1 L x min(-1)), and post exercise blood pH levels (OG: 6.98+/-0.07; RG: 7.04+/-0.07). Performance on a rowing ergometer successfully discriminates between OG and RG rowers with the best predictors of ergometer performance in SBR being height, peak ventilation, and post exercise pH.

Acid-Base Equilibrium↗
PubMed2004

Acute effects of static stretching on hip flexor and quadriceps flexibility, range of motion and foot speed in kicking a football.

The purpose of this research was to determine the effect of static stretching in a warm-up on hip flexor and quadriceps flexibility as measured by a modified Thomas test and on range of motion (ROM) of the leg and foot speed at impact in kicking a football with maximum effort. Sixteen Australian Rules (AR) footballers performed two different warm-ups on different days. One warm-up involved five minutes of sub-maximum running followed by seven practice kicks, while the other also included 4.5 minutes static stretching of the hip flexors and quadriceps after the running. A modified Thomas test was conduced before and after each warm-up. Players performed maximum effort drop punt kicks into a net while being videotaped to determine the ROM of the kicking leg and foot speed at impact with the ball. There were no significant changes in flexibility (p > 0.05) as a result of either warm-up and there were no significant differences between the warm-ups in the kicking variables (p > 0.05). It was concluded that the Thomas test may not have been sensitive to possible acute changes in flexibility from the warm-ups, and that stretching had no influence on kicking ROM or foot speed, possibly because of the complexity of the kicking skill.

Adolescent↗
PubMed2005

Effects of immediate post-game recovery procedures on muscle soreness, power and flexiblity levels over the next 48 hours.

This study investigated whether or not immediate post-game recovery procedures could enhance the rate of recovery in Australian football players in the first 48 hr after a game. Control, stretch, pool walking and hot/cold recoveries were trialled. Typical next day recovery training (25 min of pool exercise) was also performed after each game. Muscle soreness ratings and measures of flexibility (sit and reach) and power (6-s cycling sprint and vertical jump) were obtained 45 hr pre-game (Thursdays) (baseline), 15 hr post-game (Sundays, prior to "next day" recovery) and 48 hr post-game (Mondays). Performance ratios (Sunday and Monday scores divided respectively by the Thursday score) were used as the primary index of recovery. Muscle soreness was significantly greater (p<0.01) than baseline on both Sunday and Monday in all conditions, but no differences between the three recoveries and control were evident. On Sunday, vertical jump and 6-s work and power scores were only significantly lower than baseline values in control and performance ratios recorded two significant differences (vertical jump: pool walking > control, p<0.01; 6-s power: stretch > control, p<0.01) and moderate to large effect sizes (>0.3). No differences were found between the three experimental recoveries. On Monday no significant differences were recorded in performance between the recoveries and the effect sizes were of lower magnitude. In conclusion, recovery of muscle soreness, flexibility and power at 48 hr post-game was not significantly enhanced by performing an immediate post-game recovery beyond that achieved by performing only next day recovery training.

Adult↗
PubMed2002

Albumin transport analysis of different collected and processed plasma products by electron spin resonance spectroscopy.

BACKGROUND: Changes of albumin conformation flexibility and binding characteristics in plasma products can be determined by electron spin resonance spectroscopy (ESR) with spin probes as reporter molecules. METHODS: Quality of albumin transport was analyzed in different processed plasma units using a new ESR method which provides estimation of albumin properties by examination of albumin molecular structure changes. RESULTS: In serum of healthy donors could not be obtained any abnormalities. Transport function of albumin in plasma products can be influenced by various methods of plasma collection, preparation, and filtration. Evident are changes in capacity of fatty acid binding sites and ordering changes of bound substrates. Transport respiratory detoxification efficiency is decreased between 30% and 70% in all FFP compared to control values. CONCLUSIONS: ESR spectroscopy can be used as a quality test for plasma. The ESR technique has a big potential for determination of conformation changes of macromolecules and as a global tumor marker test for donor screening.

Biological Transport↗
PubMedDate not supplied

Anterior thoracic scoliosis constructs: effect of rod diameter and intervertebral cages on multi-segmental construct stability.

BACKGROUND CONTEXT: Many studies have reported on the use of anterior instrumentation for thoracolumbar scoliosis and more recently thoracic scoliosis. However, the optimal construct design remains an issue of debate. PURPOSE: To optimize construct design and enhance implant survival until a successful spinal arthrodesis is achieved. STUDY DESIGN: This study evaluated the effect of rod diameter and intervertebral cages on construct stiffness and rod strain using a long-segment, anterior thoracic scoliosis model with varying levels of intervertebral reconstruction. METHODS: Sixteen fresh-frozen calf spine specimens (T1 to L1) were divided into two groups based on rod diameter reconstruction (4 mm and 5 mm). Testing included axial compression, anterior flexion, extension and lateral bending with variations in the number and level of intervertebral cage reconstructions: apical disc (one), end discs (two), apical and end discs (three), all seven levels (seven). Multisegmental construct stiffness and rod strain were determined and normalized to the intact specimen for analysis. RESULTS: The seven-level intervertebral cage construct showed significantly greater stiffness in axial compression for both the 4-mm (366% increased stiffness) and 5-mm (607% increased stiffness) rod groups (p<.001). The remaining constructs were not significantly different from each other (p>.05). In flexion, similar results were obtained for the 4-mm construct (p<.001) but not the 5-mm construct, because the reconstruction-alone, one-, two- and three-cage constructs were all significantly stiffer than the intact specimen (p<.05). Multisegmental construct stiffness under extension loading, as well as right and left lateral bending, also exhibited significant differences between the seven-level interbody cage reconstructions and the remaining constructs. Apical rod strain for both the 4-mm-rod and 5-mm-rod groups were significantly higher for the two cage constructs (a cage at either end but not the apex where the strain gauges were located) as compared with the other constructs (p<.05). These differences were more pronounced in the 4-mm-rod group. Similar results were obtained in anterior flexion, extension and lateral bending. CONCLUSIONS: Intervertebral cages at every level significantly improved construct stiffness compared with increasing rod diameter alone. Moreover, cages markedly decreased rod strain, and when structural interbody supports were not used, axial compression created the greatest rod strain.

Animals↗
PubMedDate not supplied

Biomechanical comparison of cervical interbody cage versus structural bone graft.

BACKGROUND CONTEXT: Clinically, cervical interbody cages provide fusion rates equivalent to structural bone grafting. No published studies have biomechanically compared cages with grafts. PURPOSE: We sought to compare the stability offered by threaded interbody cages versus structural bone graft and to evaluate the additional stability provided by adding a one- or two-level anterior plate to both interbody techniques. STUDY DESIGN/SETTING: Nondestructive nonconstraining repeated-measures in vitro flexibility tests were performed on surgically instrumented specimens. SUBJECT SAMPLE: Sixteen human cadaveric specimens were separated into two groups (specimens receiving graft and specimens receiving cage) with matched bone mineral density. OUTCOME MEASURES: Angular range of motion (ROM), neutral zone (NZ) and elastic zone (EZ) were quantified to assess stability. Student's t tests compared outcomes between and within groups. METHODS: Quasistatic nonconstraining torques (maximum 1.5 Nm) induced flexion, extension, lateral bending and axial rotation while angular motion was recorded stereophotogrammetrically. Specimens were tested normal, after discectomy, with graft or cage, with two-level plate and with one-level plate. RESULTS: Graft alone and cage alone reduced ROM and EZ but not NZ to within normal. In both groups, adding a one- or two-level plate significantly reduced motion in all modes of loading. There were no significant differences in motion parameters between groups whether plated or unplated. A two-level plate provided significantly better stability than a one-level plate. CONCLUSIONS: The interbody cage performed equivalently to the structural graft. Substantial increases in stability can be gained for either interbody technique by adding an anterior plate.

Adult↗
PubMed1998

Changes in the stiffness, strength, and toughness of human cortical bone with age.

Aging adversely affects the elastic and ultimate properties of human cortical bone as seen in uniaxial tests in quasi static loading, high strain rate impact or fatigue. Little is known about the full effects of aging on toughness and its relationship with strength. In the present article the elastic modulus (E), strength (sigma f), fracture toughness (KC and J-integral), and work of fracture (Wf) were determined in specimens of male human femoral bone aged between 35-92 years. In this way we investigated whether fracture of bone in three situations, allowing various amounts of damage prior to fracture, can provide a better insight into the fracture process and also the relative importance of these experimental methods for assessing the soundness of bone material. We found a steady and significant decrease with age for all these mechanical measures. E fell by 2.3%, from its value of 15.2 GPa at 35 years of age, per decade of later life; sigma f fell similarly from 170 MPa by 3.7%; KC from 6.4 MPa m1/2 by 4.1%; J-integral from 1.2 kJ m-2 by 3%, and the Wf from 3.4 kJ m-2 by 8.7%. In aging bone there was a deterioration in the elastic properties of the material. This reduced the (elastically calculated) critical stress intensity level (KC) required to initiate a macrocrack, or the nonlinear energy associated with the onset of fracture (J). The macrocrack was preceded by less damage, and once created needed less energy to drive through the tissue (Wf).

Adult↗
PubMed2000

Passive resistance of hamstring muscles in children with severe multiple disabilities?

The purposes of this study were to evaluate whether resistance to stretch could be measured in a reproducible manner from day to day in children with severe multiple disabilities, and whether 6 weeks of daily activity, including one daily stretch, would modify passive resistance to stretch. Passive resistance to stretch was measured in six children using an established model that synchronously and continuously measured knee flexion moment (Nm) and EMG activity of the hamstring, while the velocity and angle of a static stretch was controlled. Resistance to stretch was evaluated in the absence of EMG activity. Measurements were taken on two separate occasions with a 2-week hiatus, and before and after a 6-week activity period which included a daily 1-minute static stretch. There was no significant change in resistance to stretch when tested 2 weeks apart (test 1, 8.6 +/- 1.2 Nm; test 2, 8.3 +/- 1.2 Nm, p>0.05) which yielded a strong correlation coefficient (Spearman r=1.0, p<0.01; Pearson r=0.953, p<0.01). Similarly, there was no difference in resistance to stretch before and after the 6-week period (mean difference 0.22 +/- 0.75 Nm, p>0.05). Data from this study demonstrate that resistance to stretch of the hamstring muscle group could be measured in a reproducible manner from day to day in children with multiple disabilities. Further, resistance to stretch was unchanged after 6 weeks of daily activity, including a daily 1-minute static stretch.

Adolescent↗
PubMed2005

Testing of the spinal alignment and range of motion measure: a discriminative measure of posture and flexibility for children with cerebral palsy.

In this study we describe the development and preliminary psychometric testing of the Spinal Alignment and Range of Motion Measure (SAROMM). Through consultation with pediatric physiotherapists, the items were refined. Subsequently 25 children and adolescents with cerebral palsy (CP; 17 males, 8 females) with a mean age of 9 years 8 months (SD 4y 4mo), stratified by the Gross Motor Function Classification System (GMFCS, n=5 in each group), were recruited. Twenty-two children had spastic CP, and one each was also diagnosed with hypotonic, athetoid, and mixed CP. Three children had hemiplegia, 12 had diplegia, and 10 had quadriplegia. These participants were examined by two physiotherapists on one occasion and by the primary physiotherapist again two weeks later. The intraclass correlation coefficients reflecting interrater and test-retest reliabilities for the spine and range of motion subscales and the total scores were all above 0.80. Validity was supported by a significant contribution of GMFCS level and age to the SAROMM score (r2=0.44). The SAROMM has sufficient reliability and validity for use with children with CP in clinical and research settings by rehabilitation therapists.

Adolescent↗
PubMed2006

Muscle stiffness and strength and their relation to hand function in children with hemiplegic cerebral palsy.

This study compared the passive stiffness of wrist flexors and the strength of wrist flexors and extensors in three different wrist positions (30 degrees of flexion, neutral, and 30 degrees of extension) between children with cerebral palsy (CP) and typically developing (TD) comparison children. It also examined associations between these characteristics and manual function in children with CP. Eleven children with spastic hemiplegic CP (six females, five males; mean age 8y 5mo [SD 1y 8mo], range 6-11y) and 11 TD children, matched for age and sex, took part in this study. Passive stiffness of muscles was measured as the torque/angle relation during passive motion. Isometric strength tests were performed and the time needed to complete three tasks based on the Jebsen-Taylor Hand Function Test was recorded. Flexor stiffness was higher in the group with CP. Strength of flexors and extensors in the group with CP was lower with the wrist extended. No difference among test positions was found in the TD group. Moderate correlations were observed between manual function and variables related to strength and stiffness of wrist muscles in the group with CP. Children with CP showed muscle alterations coherent with the use of the wrist in flexion. Intervention on these characteristics could have a positive impact on manual function.

Age Factors↗
PubMed1997

Flexible transnasal endoscopy: is local anaesthetic necessary?

Prior to flexible transnasal endoscopy (FTE) topical intranasal agents such as cocaine or combinations of a local anaesthetic and vasoconstrictor agent are generally recommended for local anaesthesia, easier access, and better examination of the interior of the nose, especially the middle meatus. This double-blind study involved 60 patients. Each had five per cent cocaine sprayed in one nostril and normal saline in the other. The pain/discomfort and gag scores showed no statistical difference. Forty-two (70 per cent) patients had a moderate/marked deviation of the nasal septum. A significant pain score (3-5) was obtained in 33.3 per cent of cases with the deviation towards the cocaine side and in 37 per cent of cases with the deviation towards the saline side. Ease of procedure scores for both sides were also comparable, when deviation of the nasal septum was taken into account.

Adolescent↗