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At least 19 recordsLinked to original sources

PubMed1976

Structure and function of the two heads of the myosin molecule. III. Cooperativity of the two heads of the myosin molecule, shown by the effect of modification of head A with rho-chloromercuribenzoate on the interaction of head B with F-actin.

Subfragment-1 of HMM was prepared by tryptic [EC 3.4.21.4] digestion of HMM, which had been modified with 1 mole of CMB per mole of HMM at a specific SH group, SHr. S-1(T) obtained from CMB-HMM retained almost all the CMB, and the amount of bound CMB was about 0.8-0.9 mole per 2 moles of S-1(T). S-2 of CMB-HMM contained no bound CMB. The ATPase [EC 3.6.1.3] activity of HMM increased gradually with increase in the concentration of FA, and the acto-HMM ATPase was inhibited by excess substrate or removal of Ca2+ ions in the presence of RP. The ATPase activity of CMB-HMM increased to a maximum level on adding a small amount of FA, and the acto-CMB-HMM ATPase showed neither substrate inhibition nor Ca2+ sensitivity in the presence of RP. On the other hand, the dependence on the concentration of FA of the ATPase activity of acto-S-1(T) was unaffected by modification of S-1 with CMB. The Ca2+ sensitivity of the ATPase activity of acto-S-1(T) in the presence of RP was also unaffected by the modification. Acto-S-1(T) dissociated almost completely, while acto-CMB-S-1(T) was only 50% dissociated on adding ATP. More than 80% of the bound CMB was contained in S-1(T) undissociated from FA. Furthermore, superprecipitation of actomyosin induced by ATP was completely inhibited by adding about 2 moles of CMB-S-1(T) per mole of actin monomer. On the other hand, about 90% of the burst size of Pi liberation was retained in S-1(T) dissociated from FA. It was concluded that the two heads of the myosin molecule are different: one shows the initial burst of Pi liberation, and does not contain the SHr group which binds CMB (head B), and the other does not show the initial burst and contains the SHr group (head A). It was also concluded that modification of head A of HMM or myosin with CMB increases its binding strength to FA, and consequently the substrate inhibition and Ca2+ sensitivity of acto-HMM or actomyosin ATPase at head B are lost on modification of head A with CMB. CMB-S-1(CT) was prepared by chymotryptic [EC 3.4.21.1] digestion of CMB-myosin, and separated into two fractions by ultracentrifugation of acto-CMB-S-1(CT) in the presence of ATP. Three components of CMB-S-1(CT) with molecular weights of 9, 2.4, and 1.2 X 10(4) were separated by SDS-polyacrylamide gel electrophoresis. The ratios of the peak areas of the three components in electrophoretograms were the same in CMB-S-1(CT) and in the two fractions (1 : 0.18 : 0.09), indicating that heads A and B have the same subunit structure.

Actins↗

PubMed1992

Non-icteric pancreas head carcinoma fares worse than icteric pancreas head carcinoma.

A total of 22 patients with non-icteric pancreas head carcinoma were retrospectively compared with 61 patients with icteric pancreas head carcinoma. No significant difference was found regarding age, sex, greatest diameter, macroscopic type, microscopic type, stage, lymphatic permeation, perineural infiltration, venous invasion, lymph node metastasis, and the presence of cancer cells at the surgical margins. The main location of pancreas head carcinoma could be divided into two sites: the superior (pericholedochal), and inferior or distal (excholedochal) areas of the pancreas head. Sixteen (73%) of the 22 non-icteric pancreas head carcinomas were located in the inferior or distal area (excholedochal), while 28 (46%) of the 61 icteric pancreas head carcinomas were situated in the superior portion (pericholedochal) (P less than 0.05). One (5%) of the 22 non-icteric pancreas head carcinomas was small pancreas carcinoma, compared with 11 (18%) of the 61 icteric pancreas head carcinomas. The cumulative 2-year and 4-year survival rates of the 22 patients with non-icteric pancreas head carcinoma were significantly worse than those of the 61 patients with icteric pancreas head carcinoma [7.9% vs. 24.6% (P less than 0.05) and 0% vs. 13.4% (P less than 0.01)]. These findings suggest that non-icteric pancreas head carcinomas normally arise in an area far from the biliary tree, and include a greater number of large tumors. Any resulting difficulty and delay in the diagnosis and treatment of this disease will usually lead to a worsening of the clinical course of non-icteric pancreas head carcinoma.

Age Factors↗

PubMed1992

The influence of head position and head reorientation on the axis of eye rotation and the vestibular time constant during postrotatory nystagmus.

Reorienting the head with respect to gravity during the postrotatory period alters the time course of postrotatory nystagmus (PRN), hastening its decline and thereby reducing the calculated vestibular time constant. One explanation for this phenomenon is that the head reorientation results in a corresponding reorientation of the axis of eye rotation with respect to head coordinates. This possibility was investigated in 10 human subjects whose eye movements were monitored with a three-dimensional magnetic field - search - coil technique using a variety of head reorientation paradigms in a randomized order during PRN following the termination of a 90 degrees/s rotation about earth vertical. Average eye velocities were calculated over two time intervals: from 1 s to 2 s and from 7 s to 8 s after cessation of head rotation. The time constant was estimated as one third of the duration of PRN. For most conditions, a reorientation of the head with respect to gravity 2 s after the rotation had stopped did not significantly alter the direction of the eye velocity vector of PRN with respect to head coordinates. This strongly indicates that, in humans, PRN is mainly stabilized in head coordinates and not in space coordinates, even if the otolith input changes. This finding invalidates the notion that the shortening of PRN due to reorientation of the head could be due to a change of the eye velocity vector towards a direction (torsion), which is not detectable with the eye recording methods (electrooculography) used in earlier studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

The transmission of translational seat vibration to the head: the effect of measurement position at the head.

Head motion has been measured in six axes on twelve subjects exposed to vertical seat vibration in the frequency range 0.5-25 Hz. The subjects sat on a rigid flat seat in two postures: 'back-off' (no backrest) and 'back-on' (subject's back in contact with the seat backrest). Translational acceleration has been calculated for various locations on the head and transmissibilities between vertical seat vibration and translational head motion determined for each location and all axes. The translational motion of the head was most affected by pitch motion of the head. This caused variations in fore-and-aft motion with position along the vertical axis of the head and variations in vertical motion with position along the fore-and-aft axis of the head. These variations are illustrated for each subject in both postures. The individual data allow the identification of various modes of vibration and show that seat-to-head transmissibility is greatly affected by pitch modes of the head and neck. The magnitude of motion occurring in some modes is dependent on body posture.

Adolescent↗

PubMed1976

Bacteriophage T4 head morphogenesis. VII. Terminal stages of head maturation.

Several aspects of the terminal stages of T4 head maturation were investigated using ts and am mutants blocked at single steps of the assembly pathway. We had previously found that cells infected with mutants of gene 13, e.g., tsN38 and amE609, accumulated both stable (10 to 20%)- and fragile (80%)-filled head precursors (Hamilton and Luftig, 1972). Here we showed the following for such gene 13-defective, mutant-infected cells. (i) Using thin-section analysis the pool of phage precursor structures observed under nonpermissive conditions was one-third of that observed when the cells were cultured under permissive conditions. (ii) In order for complete conversion of the precursors into viable phage to occur, there were apparent requirements of metabolic energy, protein, and DNA synthesis. (iii) The intracellular DNA pool under nonpermissive conditions exhibited a 50% distribution between 63S (mature size) and 200 S (concatenate size) DNA, with the latter DNA serving as a precursor pool. Further, this DNA pool when spread onto a protein monolayer exhibited a dispersed array of DNA, strands around a core, which was less dense than that found for the greater than 1,000S DNA concatenate isolated from gene 49-defective infected cells. (iv) When precuations were taken to stabilize the head precursors, such as lysis of the cells into glutaraldehyde, there was a 30% increase in the yield of 1,200S filled heads. Correlating these results and previous results concerning gene 49-defective unfilled heads, we propose that there are several forms of gene 13 fragile head precursors which serve as intermediates between gene 49 unfilled heads and gene 13 stable filled heads. We cannot, however, rule out the possibility that all gene 13-defective heads represent a single class of unstable particles, which decay slowly. In either case, we have shown that gene 13-defective particles are unstable to some degree inside the cell and are highly unstable outside the cell; yet all particles can still be efficiently converted to phage in vivo.

Chloramphenicol↗

PubMed1992

[A comparative study of the characteristics of femoral hip prosthesis heads--study and results ceramic-coated hip joint heads of titanium].

Today, only hard/soft cup and femoral head combinations are employed for hip joint prostheses. Highly polished ceramic is a material with very good tribological properties for femoral heads, being highly resistant to mechanical wear and tear, and highly resistant to chemical reactions in the biological environment. The advantage of metal heads, in contrast, undoubtedly lies in their resistance to breakage and the ease with which their geometry can be modified with respect, for example, to antirotation angle and neck length. The ideal material for femoral heads is a combination of the two materials. The new multi-layer combination of titanium-niobium oxide/nitride ceramic coating applied to a prehardened titanium head combines the positive material properties in an ideal manner. Femoral heads made of CoCrMo, oxide-hardened titanium, aluminium oxide or multilayer titanium-niobium ceramic were compared by means of friction an wear and tear tests. The TiNb-ceramic-metal heads showed similar abrasion at the surface as the ceramic heads. At the high loads of more than 400 kp, which may also be reached under physiological conditions, the specially coated titanium-ceramic heads proved to be superior in terms of resistance to fracture and tribological properties.

Biomechanical Phenomena↗

PubMed1992

Analysis of human red cell spectrin tetramer (head-to-head) assembly using complementary univalent peptides.

The mass-driven assembly of spectrin dimers to form tetramers involves two equal head-to-head alpha-beta associations and requires at least 30 degrees C for interconversion to occur readily. In this paper, the properties of tetramer formation were investigated using two complementary univalent peptides (the alpha I domain and beta monomers). Since the alpha I domain lacks an essential nucleation site required for side-to-side (lateral) heterodimer assembly [Speicher et al. (1992) J. Biol. Chem. 267, 14775-14782], these two peptides can only assemble head-to-head at a single site. This head-to-head assembly readily occurs at lower temperatures, indicating the temperature barrier for dimer-tetramer interconversion is caused by a conformational constraint of the dimer. This constraint, a closed hairpin loop, is released when the laterally associated partner is removed. The univalent alpha I-beta binding affinity at 37 degrees C (Ka = 1.4 x 10(5) M-1) is similar to the dimer-tetramer association constant at the same temperature. As the temperature is decreased from 37 to 0 degrees C, the alpha I-beta binding affinity increases about 32-fold. In contrast with head-to-head associations involving dimers, the second-order rate constants of two complementary univalent peptides (i.e., alpha I and beta) are dramatically higher, and the estimated activation energy (about 50 kJ mol-1) is about 5-fold lower. An open dimer conformation is an obligatory high-energy intermediate required for dimer-tetramer interconversion, and opening the dimer hairpin loop contributes about 190 kJ mol-1 to the activation energy for tetramer association.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, Gel↗

PubMed1977

Bacteriophage T4D head morphogenesis. VIII. DNA-protein associations in intermediate head structures that accumulate in gene 49--mutant-infected cells.

We have utilized the gene 49(-) mutant-infected cells of bacteriophage T4D to accumulate large numbers of nucleic acid-protein intermediate head structures. These heads were used as substrates for experiments in the investigations of the mechanism of DNA packaging. Specifically, we have examined: (i) the susceptibility of the DNA in these structures to digestion by a variety of nucleases after a series of increasing temperature pulses from 25 to 100 degrees C, (ii) the physicochemical characteristics of the DNA inside these heads, and (iii) the mechanism by which proteins are displaced from the interior of the head after treatment with basic proteins. We isolated DNA from these gene 49(-) heads by use of gradient centrifugation procedures. The DNA had a molecular weight of 8 x 10(6) and a density of 1.697 +/- 0.005 g/cm(3), and it contained a short resistant fraction (SRF) which, when associated with the gene 49(-) heads, exhibited AT-protected regions that were not susceptible to micrococcal nuclease digestion. Such a fraction may contain pieces which are important in the initial association of the DNA with the prohead. Exposure of the gene 49(-) intermediate capsid structures to basic proteins, such as bovine trypsin inhibitor, lysozyme, and l-polylysine-70, caused a displacement of an amorphous-appearing structure which may be a complex of the gene 49(-) DNA and interior components of the capsid (e.g., internal proteins, polyamines). Our general conclusion is that in the gene 49(-) intermediate head structures which are only partly filled with DNA, this DNA is held inside the head by strong electrostatic linkages with interior polypeptides and polyamines.

Capsid↗

PubMed1978

Body rocking, head banging, and head rolling in normal children.

Body rocking, head banging, and head rolling--three rhythmic behaviors that involve stimulation of the vestibular system--were studies in 525 normal children. Data analyses focused on two issues: (1) the prevalence and duration of these habits and their relationship to child and family factors and (2) the hypothesis that children who persistently displayed such behaviors would be reported as developmentally more advanced than "non-self-stimulators." Body rocking was the earliest to appear and most prevalent of the three habits. Head banging and head rolling had roughly the same prevalence and age of onset. Comparisons of "self-stimulators" with "non-self-stimulators" yielded no significant effects for birth order or SES; only for head banging was a significant (3:1) ratio of males to females found. A comparison of the ages at which 12 "milestones" first appeared supported the hypothesis of developmental precocity for the body rockers and the head bangers, but not for the head rollers.

Birth Order↗

PubMed1978

The relationship between head and eye movement in congenital nystagmus with head shaking: objective recordings of a single case.

Head shaking and congenital nystagmus were recorded in a patient presented with visual tasks. When she was at rest the nystagmus took a 6 cycles per second saw-tooth wave-form. When she was attentive the nystagmus beat at a 2 to 2.6 cycles per second with a saddle-shaped deformation which permitted foveation. The head shaking occurred occasionally when the patient was attentive and was phase-locked to the nystagmus with resemblances in wave form and direction. Deceleration of the head shaking to zero velocity and peak displacement (to the left) coincided with the onset of the saddle of the nystagmus and hence assisted foveation; all other parts of the head-shaking cycle were detrimental to vision. It is proposed that the head shaking has a common pathological origin with the nystagmus and that, just as an isolated congenital nystagmus wave form becomes altered with attention to permit periods of foveal fixation, the pattern of combined head and eye nodding in this patient provided similar peroids of fixation.

Adult↗

PubMed1992

Ictal head deviation: lateralizing significance of the pattern of head movement.

To resolve the controversy surrounding the lateralizing value of ictal head deviation, we analyzed head-turning movements in relation to the actions of the two divisions of the sternocleidomastoid muscle. In 12 (75%) of 16 patients with surgically confirmed lateralized seizure foci, the face rotated upward and contraversive to the hemisphere of seizure origin, consistent with activation of the ipsilateral sternomastoid muscle. One patient showed a sustained, downward ipsiversive head tilt consistent with the action of the ipsilateral cleidomastoid muscle, and three patients had a combined ipsiversive head tilt and contraversive face rotation. No patient exhibited ipsiversive upward face rotation or contraversive head tilting, as would be expected if the contralateral sternocleidomastoid were activated. Our findings indicate that hemispheric seizure foci activate one or both divisions of the ipsilateral sternocleidomastoid muscle. Accurate lateralization of the seizure focus is possible only when ictal head deviation is assessed in the context of the different actions of the sternomastoid and cleidomastoid muscle divisions.

Adolescent↗

PubMed1992

[Osteonecrosis of the femoral head in spontaneously hypertensive rats--electron microscopic study of the growth plate in the femoral head].

The growth plate of the femoral heads in growing spontaneously hypertensive rats (SHRs) was investigated histologically and ultrastructurally, to clarify the causes of femoral head lesions: osteonecrosis and/or ossification disturbance of the epiphysis. As compared with the normal femoral heads, histological abnormalities of the growth plate in the weight-bearing area of the femoral heads, such as decreased thickness and nodular formation etc., frequently accompanied femoral head lesions. Ultrastructural observation disclosed that the most of chondrocytes in the growth plate with decreased thickness were in the degenerative condition. Chondrocytes in nodular formation showed the fine structure reflecting the accelerated cell metabolism or mild degeneration indicating the regenerative process. It suggested that the disorder of chondrocytes would weaken the architecture of the cartilaginous canal where the blood vessels pass to the proximal femoral epiphysis, and that the obstruction of the cartilaginous canal would cause the femoral head lesions in SHRs.

Animals↗

PubMedDate not supplied

Evidence for head-head interactions in myosin from cardiac and skeletal muscles.

1. Binding of MG-ADP to both heart and fast skeletal myosin was found with 3 methods to proceed in 2 steps. One mole of MG-ADP binds with high affinity (K approximately equal to 10(6) M-1) and subsequently a second with lower affinity (K approximately equal to 10(2)-10(4) M-1) per myosin. Only one mole of MG-ADP was found to bind with the high affinity to isolated myosin heads. This implies that binding of MG-ADP to intact myosin exhibits negative cooperativity. 2. When a nucleotide is bound, the 2 heads of a single myosin molecule adopt different conformations since on each head a different type of essential thiol group was found to be the most reactive towards N-ethylmaleimide. In the presence of MG-pyrophosphate a thiol-1 is the most reactive essential group in both heads. Therefore, the nucleoside moiety seems to be required for this latter type of head-head interaction.

Adenosine Diphosphate↗

PubMed1976

Head morphologies in bacteriophage T4 head and internal protein mutant infections.

Escherichia coli infected with phage T4 mutants defective in synthesis of the three major internal proteins found in the phage head, IPI-, IPII-, IPIII-, or IP degrees (lacking all three) were examined in the electron microscope for head formation. Infection with IPI- or IPII- does not appear to induce increased aberrant head formation, whereas IPII- or IP degrees infections result in production of polyheads and viable phage. Multiple mutants of the early head formation genes 20, 21, 22, 23, 24, 31, 40 and IP degrees were constructed. Combination with IP degrees increases polyhead formation when head formation is not blocked at a more defective stage but results in a qualitative shift to lump formation in association with gene 22 mutants. Thin-sectioning studies show morphologically similar cores in amber 21 and 21am IP degrees tau particles. These morphological observations, genetic evidence for interaction between ts mutants in gene 22 and the IP mutants, and analysis of the protein composition of tau particles further support the idea that p22 and the internal proteins form an unstable assembly core necessary for an early stage of head formation (M. K. Showe and L. W. Black, 1973).

Coliphages↗

PubMed1975

Homoeotic effect of the tumorous-head mutant and differential effect of an enhancer gene in the tumorous-head strain of Drosophila melanogaster.

Homoeotic effects (one organ replaced by an organ from a different part of the body) were investigated in the tumorous-head phenotype in Drosophila melanogaster. The tumorous-head mutant is the only known maternally effected homoeotic mutant (Postlethwait and Schneiderman, 1973). As reported by Postlethwait et al. (1972) transformations from eye to abdominal like structures, eye to antennal like structures, eye to palpus like structures, rostralhaut to genital like structures, rostralhaut to clasper teeth, and rostralhaut to antennal like structures were observed. Transformations currently observed but not by Postlethwait et al. (1972) are: eye to genital structures (resembling anal plates in both sexes or lateral plates in males); antenna to genital like structures; rostralhaut to abdominal like structures; and proboscis to leg like structures. Since a tumorous-head strain selected for high penetrance and expressivity was used for this study, differences between the two studies are ascribed to strain selection. Effect of a third chromosome gene which acts to enhance the tumorous-head maternal effect was also investigated. A highly significant increase in expressivity was found especially in females. Of 4,730 female flies examined possessing the enhancer gene, high penetrance and high expressivity, only the eye-antennal imaginal disc and possibly the libial disc showed destabilization. We observed no destabilization of the wing disc by the tumorous-head genes as predicted by Kauffman (1973).

Animals↗

PubMed1992

Rat cardiovascular responses to whole body suspension: head-down and non-head-down tilt.

The rat whole body suspension technique mimics responses seen during exposure to microgravity and was evaluated as a model for cardiovascular responses with two series of experiments. In one series, changes were monitored in chronically catheterized rats during 7 days of head-down tilt (HDT) or non-head-down tilt (N-HDT) and after several hours of recovery. Elevations of mean arterial (MAP), systolic, and diastolic pressures of approximately 20% (P < 0.05) in HDT rats began as early as day 1 and were maintained for the duration of suspension. Pulse pressures were relatively unaffected, but heart rates were elevated approximately 10%. During postsuspension (2-7 h), most cardiovascular parameters returned to presuspension levels. N-HDT rats exhibited elevations chiefly on days 3 and 7. In the second series, blood pressure was monitored in 1- and 3-day HDT and N-HDT rats to evaluate responses to rapid head-up tilt. MAP, systolic and diastolic pressures, and HR were elevated (P < 0.05) in HDT and N-HDT rats during head-up tilt after 1 day of suspension, while pulse pressures remained unchanged. HDT rats exhibited elevated pretilt MAP and failed to respond to rapid head-up tilt with further increase of MAP on day 3, indicating some degree of deconditioning. The whole body suspended rat may be useful as a model to better understand responses of rats exposed to microgravity.

Animals↗

PubMed1976

Cell division patterns in the Drosophila head disc: clones on the head cuticle.

An account of the patterns of clones induced on the head cuticle of Drosophila melanogaster is given. The system was studied using mitotic recombination, induced by X-rays at certain developmental stages. In agreement with the findings of a computer model devised to simulate growth in the head imaginal disc, cuticle clones are found to have a characteristic pattern, sweeping round the central, eye-forming part of the disc. The similarity between model and experiment suggests the validity of the model assumption. It is also shown that cuticle clones are not smaller in the posterior of the head, when induced at the developmental stages studied: this is in contrast to clones in the compound eye, where posterior clones are smaller than anterior ones.

Animals↗

PubMed1978

Head maturation pathway of bacteriophages T4 and T2. IV. In vitro transformation of T4 head-related particles produced by mutants in gene 17 to capsid-like structures.

T4 mutants in gene 17 accumulate particles which contain the main head protein in the cleaved form (gp23*) arranged in an unexpanded lattice (empty small particles), together with other expanded capsids (empty large particles). The isolated empty small particles can be transformed in vitro, by lowering the ionic strength, to capsid-like structures. This structural transformaton is not coupled to chemical modification of the structural proteins of the empty small particles. In contrast to unexpanded particles that are easily dissociated, the transformed structures are as resistant to dissociation as other T-even head-related particles with expanded lattice. Furthermore, the transformed particles are able to bind in vitro hoc and soc proteins, rendering capsids indistinguishable from the normal T4 capsids both morphologically and by their stability against denaturing agents. Our results indicate that the in vitro transformation of the empty small particles might mimic important and characteristic aspects of the in vivo maturation of T4 heads, thus suggesting a possible role of the "cleaved but unexpanded" particle in the maturation pathway of the T4 shell.

Capsid↗