Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “HOPS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed2005

Neuromechanical adaptation to hopping with an elastic ankle-foot orthosis.

When humans hop or run on different surfaces, they adjust their effective leg stiffness to offset changes in surface stiffness. As a result, the overall stiffness of the leg-surface series combination remains independent of surface stiffness. The purpose of this study was to determine whether humans make a similar adjustment when springs are placed in parallel with the leg via a lower limb orthosis. We studied seven human subjects hopping in place on one leg while wearing an ankle-foot orthosis. We used an ankle-foot orthosis because the ankle joint is primarily responsible for leg stiffness during hopping. A spring was added to the ankle-foot orthosis so that it increased orthosis stiffness by providing plantar flexor torque during ankle dorsiflexion. We hypothesized that subjects would decrease their biological ankle stiffness when the spring was added to the orthosis, keeping total ankle stiffness constant. We collected kinematic, kinetic, and electromyographic data during hopping with and without the spring on the orthosis. We found that total ankle stiffness and leg stiffness did not change across the two orthosis conditions (ANOVA, P > 0.05). This was possible because subjects decreased their biological ankle stiffness to offset the orthosis spring stiffness (P < 0.0001). The reduction in biological ankle stiffness was accompanied by decreases in soleus, medial gastrocnemius, and lateral gastrocnemius muscle activation (P < 0.0002). These results suggest that an elastic exoskeleton might improve human running performance by reducing muscle recruitment.

Adaptation, Physiological↗
PubMed2005

The mechanics of jumping versus steady hopping in yellow-footed rock wallabies.

The goal of our study was to explore the mechanical power requirements associated with jumping in yellow-footed rock wallabies and to determine how these requirements are achieved relative to steady-speed hopping mechanics. Whole body power output and limb mechanics were measured in yellow-footed rock wallabies during steady-speed hopping and moving jumps up to a landing ledge 1.0 m high (approximately 3 times the animals' hip height). High-speed video recordings and ground reaction force measurements from a runway-mounted force platform were used to calculate whole body power output and to construct a limb stiffness model to determine whole limb mechanics. The combined mass of the hind limb extensor muscles was used to estimate muscle mass-specific power output. Previous work suggested that a musculoskeletal design that favors elastic energy recovery, like that found in tammar wallabies and kangaroos, may impose constraints on mechanical power generation. Yet rock wallabies regularly make large jumps while maneuvering through their environment. As jumping often requires high power, we hypothesized that yellow-footed rock wallabies would be able to generate substantial amounts of mechanical power. This was confirmed, as we found net extensor muscle power outputs averaged 155 W kg(-1) during steady hopping and 495 W kg(-1) during jumping. The highest net power measured reached nearly 640 W kg(-1). As these values exceed the maximum power-producing capability of vertebrate skeletal muscle, we suggest that back, trunk and tail musculature likely play a substantial role in contributing power during jumping. Inclusion of this musculature yields a maximum power output estimate of 452 W kg(-1) muscle. Similar to human high-jumpers, rock wallabies use a moderate approach speed and relatively shallow leg angle of attack (45-55 degrees) during jumps. Additionally, initial leg stiffness increases nearly twofold from steady hopping to jumping, facilitating the transfer of horizontal kinetic energy into vertical kinetic energy. Time of contact is maintained during jumping by a substantial extension of the leg, which keeps the foot in contact with the ground.

Analysis of Variance↗
PubMed1987

Do cardiorespiratory frequencies show entrainment with hopping in the tammar wallaby?

Breathing, heart and gait frequencies, tidal volume, cardiac output, and rates of oxygen consumption were measured in tammar wallabies (Macropus eugenii Desmarest) hopping on a treadmill. At speeds greater than 1.6 ms-1 the rate of metabolic power consumption was independent of hopping speeds. Blood lactate levels within the speed range where VO2 was independent of speed showed a mean increase of 4.8 mmol l-1. During bipedal hopping, the frequencies of breathing and limb movement are phase-locked in the ratio of 1:1. Inspiration begins as the animal leaves the ground and may be a passive process driven by a visceral piston. A relatively large central tendon in the diaphragm may correlate this function. Unlike breathing frequencies, cardiac frequencies show no entrainment with hopping. The site of dissipation of the presumed large arterial pressure excursion is unknown.

Animals↗
PubMed2000

Terrestrial locomotion in the black-billed magpie: kinematic analysis of walking, running and out-of-phase hopping.

The inter-limb kinematic patterns of walking, running and out-of-phase hopping in black-billed magpies (Pica pica) were studied using high-speed video recordings. The flexion/extension patterns of the joints were similar between the gait types, suggesting that the within-leg control of the angular excursions is similar. This result is further supported by the fact that running and hopping are alternative gaits at speeds higher than walking; however, magpies show a preference for hopping. Moreover, only small differences occur between the kinematic patterns of the two limbs during out-of-phase hopping, during which the legs are believed to have different functions. The hindlimb kinematic patterns of magpies are like those of other flying and more terrestrial bird species; however, striking differences are found in comparison with humans at the level of the internal angles. This is probably due to the differences in the morphology and configuration of their legs.

Animals↗
PubMed2005

Probing the mechanical folding kinetics of TAR RNA by hopping, force-jump, and force-ramp methods.

Mechanical unfolding and refolding of single RNA molecules have previously been observed in optical traps as sudden changes in molecular extension. Two methods have been traditionally used: "force-ramp", with the applied force continuously changing, and "hopping". In hopping experiments the force is held constant and the molecule jumps spontaneously between two different states. Unfolding/refolding rates are measured directly, but only over a very narrow range of forces. We have now developed a force-jump method to measure the unfolding and refolding rates independently over a wider range of forces. In this method, the applied force is rapidly stepped to a new value and either the unfolding or refolding event is monitored through changes in the molecular extension. The force-jump technique is compared to the force-ramp and hopping methods by using a 52-nucleotide RNA hairpin with a three-nucleotide bulge, i.e., the transactivation response region RNA from the human immunodeficiency virus. We find the unfolding kinetics and Gibbs free energies obtained from all three methods to be in good agreement. The transactivation response region RNA hairpin unfolds in an all-or-none two-state reaction at any loading rate with the force-ramp method. The unfolding reaction is reversible at small loading rates, but shows hysteresis at higher loading rates. Although the RNA unfolds and refolds without detectable intermediates in constant-force conditions (hopping and force-jump), it shows partially folded intermediates in force-ramp experiments at higher unloading rates. Thus, we find that folding of RNA hairpins can be more complex than a simple single-step reaction, and that application of several methods can improve understanding of reaction mechanisms.

Base Sequence↗
PubMed2005

Optimization of conditions for supercritical fluid extraction of flavonoids from hops (Humulus lupulus L.).

Waste hops are good sources of flavonoids. Extraction of flavonoids from waste hops (SC-CO(2) extracted hops) using supercritical fluids technology was investigated. Various temperatures, pressures and concentrations of ethanol (modifier) and the ratio (w/w) of solvent to material were tested in this study. The results of single factor and orthogonal experiments showed that at 50 degrees C, 25 MPa, the ratio of solvent to material (50%), ethanol concentration (80%) resulted in maximum extraction yield flavonoids (7.8 mg/g). HPLC-MS analysis of the extracts indicated that flavonoids obtained were xanthohumol, the principal prenylflavonoid in hops.

Chromatography, High Pressure Liquid↗
PubMed2000

Combined effect of hop resins and sodium hexametaphosphate against certain strains of Escherichia coli.

The combined antimicrobial effects of hop resins with sodium hexametaphosphate, glycerol monocaprate, and lysozyme were investigated aiming to make an effective agent against Escherichia coli. When they are used separately, the antimicrobial activity against E. coli was minimal. However, the combination of hop resins with sodium hexametaphosphate exhibited strong antimicrobial activity against E. coli, but no effect was found in combinations of hop resins with the other agents. The activity was strongest when the combination was added at the beginning of growth of the bacteria, resulting in a prolonged lag phase. However, when the antimicrobials were added during the log phase, growth was depressed considerably. By addition of these materials, cell components with absorbance near 260 nm were leaked out. This possibly may have resulted from damage to the cell membranes of the bacteria. The combined effect was also detected in model food systems such as mashed potatos. The use of hop resins and sodium hexametaphosphate in combination may thus be useful for controlling E. coli.

Animals↗
PubMed2002

Oestrogenic activity of the hop phyto-oestrogen, 8-prenylnaringenin.

The female flowers of the hop plant (hop cones) are used as a preservative and as a flavouring agent in beer. A novel phyto-oestrogen, 8-prenylnaringenin, was recently identified in hops and this study was undertaken to characterize the oestrogenic activity of this compound using a combination of in vitro and in vivo assays. Natural and semi-synthetic 8-prenylnaringenin showed similar bioactivities both in a yeast screen transfected with the human oestrogen receptor and in oestrogen-responsive human Ishikawa Var-I cells. 8-Prenylnaringenin showed comparable binding activity to both oestrogen receptor isoforms (ER alpha and ER beta). 8-Prenylnaringenin extracted from hops contains similar amounts of both (R)- and (S)- enantiomers, indicating that the compound is normally formed non-enzymatically. Both enantiomers showed similar bioactivity in vitro and similar binding characteristics to ER alpha and ER beta. The oestrogenic activity of 8-prenyl-naringenin in vitro was greater than that of established phyto-oestrogens such as coumestrol, genistein and daidzein. The high oestrogenic activity was confirmed in an acute in vivo test using uterine vascular permeability as an end point. When the compound was given to ovariectomized mice in their drinking water, oestrogenic stimulation of the vaginal epithelium required concentrations of 100 mug ml(-1) (about 500-fold greater than can be found in any beer).

Animals↗
PubMed2001

Virus-infections of wild hops in Hamburg.

More than 200 samples from wild hops were collected in the city of Hamburg and tested for the presence of PNRV/ApMV, ArMV, HLV and HMV. All viruses were detected, but in case of the ilarviruses (ApMV/PNRV) no reaction was found in DAS-ELISA using ApMV antiserum, indicating, that, different to earlier results mainly from wild hops of southern areas of Germany, neither A nor I-types were present, but only C-type corresponding to the cherry strains of PNRV. Compared to results from escaped and cultivated hops, infestation was rather low but differing to some extent from data obtained for wild hops in other, mainly non-urban regions.

Enzyme-Linked Immunosorbent Assay↗
PubMedDate not supplied

Identification of the antibiotic hops component, colupulone, as an inducer of hepatic cytochrome P-4503A in the mouse.

A higher level of cytochrome P-450 (P450)-dependent ethylmorphine (EM) N-demethylase activity was observed in hepatic microsomes from mice fed a natural-ingredient diet ("crude diet") than in those from mice fed a semi-purified diet ("purified diet"). This led to the testing of individual ingredients of the crude diet as inducers of the P-450 system. Brewers yeast proved to be the most significant inductive component of the crude diet. Further investigation revealed that hop components (lupulones) absorbed on yeast during the brewing process were responsible for the induction of the P-450 system. The induction of P-450 and several P-450-dependent monooxygenase activities (EM N-demethylation, aniline hydroxylation, benzo[a]pyrene hydroxylation) by colupulone with respect to dose and time course were investigated. The very large increase in EM N-demethylase activity elicited by colupulone suggested that P-4503A had been induced. Western blot technology verified this speculation. Western blot analysis of microsomal protein from mice fed hops, brewers yeast, or the residue of a hexane extract of hops supported the conclusion that all of these substances induced P-4503A. These substances were also relatively good inducers of P-4502B, but not as inductive of this isozyme as the crude diet. This is interpreted to mean that not all of the inductive properties of the crude diet are due to hop components. These studies question the use of crude commercial diets in studies of P-450 systems. They may also challenge some current definitions of "constitutive" and "induced" P-450s.

Animals↗
PubMed2003

Health effects of inhalation exposure to organic dust in hops farmers.

Medical examinations were performed in a group of 23 hops farmers exposed to organic dust from hop (Humulus lupulus). The examinations took place in individual farms during harvesting, sorting and transporting of hop cones. As a reference group, 50 urban dwellers not exposed to organic dust were examined. There were conducted physical examinations, interviews concerning the occurrence of respiratory disorders and work-related symptoms, lung function tests, determination of cytokines concentrations, and allergological tests comprising skin prick test with 4 microbial antigens associated with organic dust, precipitin test with 12 microbial antigens, and a test for inhibition of leukocyte migration. Five farmers (21.7%) reported occurrence of work-related symptoms, including dry cough and dyspnoea. Eight farmers (34.8%) reported symptoms of chronic bronchitis. Mean spirometric values were within normal ranges. The farmers showed positive responses in precipitin test and test for inhibition of leukocyte migration to antigens of environmental microbes, mainly to the antigen of Gram-negative bacterium Pantoea agglomerans. The results showed a potential risk of occupational respiratory diseases in the population of hops farmers.

Adult↗
PubMedDate not supplied

Liquid chromatographic method for determination of total avermectin B1 and 8,9-Z-avermectin B1 residues in hops.

A liquid chromatographic method has been developed and validated for determination of avermectin B1 and 8,9-Z-avermectin B1 residues in dried hops. The dried hops are rehydrated and subsequently extracted with a methanol-water mixture. The avermectins are partitioned into hexane and the hexane extract is concentrated (purified) on an aminopropyl solid-phase extraction column. The purified extract is derivatized with trifluoroacetic anhydride, and the derivatized avermectins are analyzed by reversed-phase liquid chromatography with fluorescence detection. Recoveries of the avermectins from dried hops fortified with approximately 5-1000 ng/g avermectin B1a or 8,9-Z-avermectin B1a ranged from 73 to 108% with an overall average recovery of 95%. The limit of quantitation is 5 ng/g (signal-to-noise ratio [S/N] > 10), and the limit of detection is 2 ng/g (S/N > 3) for each analyte. The assay procedure provides a simple, rapid, and sensitive method for monitoring the total avermectin residues in hops.

Chromatography, Liquid↗
PubMed1994

Crystallization and preliminary crystallographic data of recombinant human osteogenic protein-1 (hOP-1).

We have obtained trigonal crystals of recombinant human osteogenic protein-1 (hOP-1), a member of the transforming growth factor-beta (TGF-beta) superfamily. hOP-1 (also referred to as BMP-7) is a bone morphogenetic protein and is active as a dimer of M(r) 32 to 36 kDa. The crystals have the symmetry of space group P3(1)21 or the enantiomorph P3(2)21 with unit cell dimensions of a = b = 99.46 A, c = 42.09 A. The crystals diffract to 2.2 A resolution and there is one hOP-1 monomer per asymmetric unit. In this paper we describe the first crystallization of a bone morphogenetic protein and present the results of preliminary X-ray diffraction data from the native protein and two heavy-atom derivatives.

Bone Morphogenetic Protein 7↗
PubMed2001

The variability of hop latent viroid as induced upon heat treatment.

We have previously shown that heat treatment of hop plants infected by hop latent viroid (HLVd) reduces viroid levels. Here we investigate whether such heat treatment leads to the accumulation of sequence variability in HLVd. We observed a negligible level of mutated variants in HLVd under standard cultivation conditions. In contrast, the heat treatment of hop led to HLVd degradation and, simultaneously, to a significant increase in sequence variations, as judged from temperature gradient-gel electrophoresis analysis and cDNA library screening by DNA heteroduplex analysis. Thirty-one cDNA clones (9.8%) were identified as deviating forms. Sequencing showed mostly the presence of quadruple and triple mutants, suggesting an accumulation of mutations in HLVd during successive replication cycles. Sixty-nine percent of base changes were localised in the left half and 31% in the right half of the secondary structure proposed for this viroid. No mutations were found in the central part of the upper conserved region. A "hot spot" region was identified in a domain known as a "pathogenicity domain" in the group representative, potato spindle tuber viroid. Most mutations are predicted to destabilise HLVd secondary structure. All mutated cDNAs, however, were infectious and evolved into complex progeny populations containing molecular variants maintained at low levels.

Base Sequence↗
PubMed2003

Regeneration and Agrobacterium-mediated transformation of hop (Humulus lupulus L.).

An efficient procedure for direct organogenesis and regeneration of hop (Humulus lupulus L.) was established. For the first time Agrobacterium-mediated genetic transformation of hop (cv. "Tettnanger") was achieved. Shoot internodes from in vitro cultures were identified as the most suitable type of explant for regeneration. Using this type of explant, a shoot-inducing medium was developed that supported direct organogenesis of approximately 50% of the explants. Plantlets were successfully rooted and transferred to the greenhouse. Overall, in less than 6 months hop cultures propagated in vitro were regenerated to plants in the greenhouse. Agrobacterium-mediated genetic transformation was performed with the reporter gene GUS (beta-glucuronidase). The presence and function of transgenes in plants growing in the greenhouse was verified by PCR (polymerase chain reaction) and enzyme assay for GUS activity, respectively. We have obtained 21 transgenic plants from 1,440 explants initially transformed, yielding an overall transformation efficiency of 1.5%.

Base Sequence↗
PubMed1983

Recovery of the hopping response after complete spinal cord transection in the cat.

The hopping response reappears in the hind limb of the cat after complete spinal cord transection at postoperative day means = 11.6. This response is hypermetric and slow compared with that in the normal cat and only forward, medial, and lateral hopping can be elicited. Anatomical and physiological changes in the spinal cord which may account for the reappearance of the hopping response are discussed.

Animals↗
PubMed1993

Improvements to the magic angle hopping experiment.

Several improvements to the magic angle hopping experiment first introduced by Bax et al. [J. Magn. Reson., 52 (1983) 147] are presented. A dc servo motor driven sample hopping mechanism which requires less than 60 ms to accomplish a 120 degrees sample rotation is described. Modifications to the data acquisition process, including starting the acquisition period immediately after the second hop and acquiring a hypercomplex data set, are also presented. Principal values of the 13C chemical shielding tensor are measured for 1,2,3-trimethoxybenzene and 2,6-dimethoxynaphthalene.

Magnetic Resonance Spectroscopy↗
PubMed2006

Analysis of xanthohumol and isoxanthohumol in different hop products by liquid chromatography-diode array detection-electrospray ionization tandem mass spectrometry.

An analytical methodology based on the sample extraction with methanol/formic acid by ultra-sonication and subsequent analysis by high-performance liquid chromatography with diode array detection is proposed for the determination of xanthohumol (XN) and isoxanthohumol (IXN) in different hop products. The identity of the compounds was confirmed by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry in positive ion mode. The performance of the method was assessed by the evaluation of parameters such as absolute recovery, repeatability, linearity and limits of detection and quantitation. This methodology was applied to investigate the impact of the extraction process of the hop products on the amount of xanthohumol and isoxanthohumol. The ethanolic extract revealed to be the hop product richest in xanthohumol (3.75+/-0.05 g/100 g) relatively to the pellets (0.62+/-0.01 g/100 g) and supercritical CO2 extract (0.089+/-0.001 g/100 g).

Chromatography, High Pressure Liquid↗