Treadmill vs. floor walking: kinematics, electromyogram, and heart rate

To identify the degree of difference between treadmill and floor walking, kinematic, electromyographic (EMG), and heart rate measurements were recorded in seven normal female subjects during walking at three speeds on the treadmill and on the floor. During treadmill walking, subjects tended to use a faster cadence and shorter stride length than during floor walking. In addition the displacements of the head, hip, and ankle in the sagittal plane showed statistically significant differences between floor and treadmill walking. Average EMG activity was usually greater on the treadmill than on the floor; however, this difference was only significant for the quadriceps. Heart rate was significantly higher during fast treadmill walking than floor walking. In general, treadmill walking was not found to differ markedly from floor walking in kinematic measurements or EMG patterns.     

Genetic analysis and molecular cloning of the Escherichia coli ruv gene

Summary The genetic organisation of the ruv gene, a component of the SOS system for DNA repair and recombination in Escherichia coli, was investigated. New point mutations as well as insertions and deletions were generated using transposon Tn10 inserted in eda as a linked marker for site specific mutagenesis, or directly as a mutagen. The mutations were ordered with respect to one another and previously isolated ruv alleles by means of transductional crosses. The direction of chromosome mobilization from ruv:: Mud(Ap^R lac)strains carrying F42lac ⁺ established that ruv is transcribed in a counterclockwise direction. Recombinant phages able to restore UV resistance to ruv mutants were identified, and the ruv ⁺ region was subcloned into a low copy number plasmid. The ruv ⁺ plasmid was able to correct the extreme radiation sensitivity and recombination deficiency of ruv recBC sbcB strains.     

Three-dimensional structure of a membrane-microtubule complex

The unicellular algae Distigma proteus contain a group of aligned microtubules associated with their cell membrane. The association is maintained in isolated membrane fragments. The membrane-microtubule complex also includes a crystalline array of membrane particles. The major peptide component of this array was identified by labeling whole cells with radioiodine. The entire complex of membrane, particles, and microtubules is sufficiently well ordered to permit reconstruction from electron micrographs by Fourier techniques. A three-dimensional model of the membrane array at a nominal resolution of 2.5 nm has been calculated. Some similarities were apparent between lattice spacings in the membrane array and in microtubules. Analysis of these lattice correlations suggests a way in which the array of membrane particles may serve as scaffolding for microtubule attachment.     

Control mechanisms governing the infectivity of Chlamydia trachomatis for HeLa cells: mechanisms of endocytosis

The mechanism by which Chlamydia trachomatis is endocytosed by host cells is unclear. Studies of the kinetics of chlamydial attachment and uptake in the susceptible HeLa 229 cell line showed that chlamydial endocytosis was rapid and saturable but limited by the slow rate of chlamydial attachment. To overcome this limitation and to investigate the mechanism of endocytosis, chlamydiae were centrifuged onto the host cell surface in the cold to promote attachment. Endocytosis of the adherent chlamydiae was initiated synchronously by rapid warming to 36 degrees C. Electron micrographs of chlamydial uptake 5 min after onset showed that chlamydial ingestion involves movement of the host cell membrane, leading to interiorization in tight, endocytic vacuoles which were not clathrin coated. Chlamydial ingestion was not inhibited by monodansylcadaverine or amantadine, inhibitors of receptor-mediated endocytosis and chlamydiae failed to displace [3H]sucrose from micropinocytic vesicles. Chlamydial endocytosis was markedly inhibited by cytochalasin D, an inhibitor of host cell microfilament function, and by vincristine or vinblastine, inhibitors of host cell microtubules. Hyperimmune rabbit antibody prevented the ingestion of adherent chlamydiae, suggesting that endocytosis requires the circumferential binding of chlamydial and host cell surface ligands. These findings were incompatible with the suggestion that chlamydiae enter cells by taking advantage of the classic mechanism of receptor-mediated endocytosis into clathrin-coated vesicles, used by the host cell for the internalization of beta-lipoprotein and other macromolecules, but were consistent with the hypothesis that chlamydiae enter cells by a microfilament-dependent zipper mechanism.     

Gamma-T4 hybrid bacteriophage carrying the thymidine kinase gene of bacteriophage T4.

Among 32 lambda-T4 recombinant phages selected for growth on a thymidylate synthetase-deficient (thyA) host, 2 were shown to carry the T4 thymidine kinase (tk) gene. The lambda-T4tk phages contain two T4 HindIII DNA fragments (2.0 and 1.5 kilobases) that hybridize to restriction fragments of T4 DNA, encompassing the tk locus at 60 kilobases on the T4 map. The T4tk insert compensates for the simultaneous host deficiencies of thymidine kinase and thymidylate synthetase in a thymidine kinase-deficient (tdk) host growing in the presence of fluorodeoxyuridine when provided with thymidine and uridine. The lambda-T4tk hybrid phages specified five polypeptides with Mrs of 22,000 (22K), 21K, 14K, 11K, and 9K.     

Monoclonal antibodies to the two most basic papaya proteinases

The proteinases fromCarica papaya include papain, isoenzymes of chymopapain and two proteinases A and B distinguished by their unusually high pI. The identity of one of the most basic proteinases has been questioned. The present report describes the preparation and characterisation of two monoclonal antibodies that react specifically with papaya proteinases A and B respectively and a third that identifies a common structural feature found in papain and proteinase A.     

Effects of cold stress and exercise on fat loss in females

A Latin Square design has been used to test the responses of 24 relatively fit young women to 200 minute bouts of exercise performed over 5 day trials under each of three different ambient conditions: 15 degrees C (warm-warm; (WW)); -20 degrees C while inhaling, from a facemask, air heated to 18 degrees C (cold-warm; (CW)); and -20 degrees C (cold-cold; (CC)). In both of the cold environments, special clothing and boots were provided (insulation 0.47 degree C X watt-1 X m-2 and 0.62 degree C X watt-1 X m-2; (4 and 3 CLO units)). All three trials led to a small (0.6-0.7 degree C) rise of rectal temperature, but in the two cold environments mean body temperatures fell by over 1.0 degree C. A large increase of serum ketones occurred under all conditions, and the exercise respiratory quotient suggested some increase of fat utilization, WW (0.85) through CW (0.84) to CC (0.83). A fat loss of about 0.5 kg over the five days was confirmed by hydrostatic weighing and measurement of skinfold thicknesses. This was much less than the change previously observed in men, and moreover, it seemed to be independent of ambient conditions. Possible reasons why cold did not increase fat loss in these women include: a lower relative intensity of exercise; a greater stability of fat stores in women; avoidance of caffeine; a possible translocation of subcutaneous fat to deep fat depots; and a greater desire to "lose weight" irrespective of environmental conditions.     

Effects of colcemid and taxol on microtubules and intermediate filaments in chick embryo fibroblasts

Reports on how changes in microtubule (MT) distribution or polymerization affect the distribution of intermediate filaments (IFs) differ. Therefore, we have used cytoimmunofluorescence techniques and electron microscopy to systematically examine and compare the arrangements of MTs and IFs in cultures of chick embryo fibroblasts under the following conditions: at different times during the cell cycle, in the presence of Colcemid or of taxol, in the presence of both drugs in succession or simultaneously in varying ratios, and during recovery from treatment with Colcemid or taxol. We have found that depolymerization of MTs by 1 microM Colcemid resulted in the rapid formation of massive IF-cables, structures distinct from "collapsed IFs" or "juxtanuclear coils." Neither the rapid formation of IF-cables nor their dispersion during recovery required protein synthesis. Cells treated with 10 microM taxol rapidly formed MT-bundles, as well as aggregates of intertwining IFs, termed "IF-skeins." MT-bundles and IF-skeins displayed strikingly complementary distributions. This reciprocal distribution of packed MTs and IFs was also obvious in untreated anaphase and telophase cells. When 10 microM taxol and 1 microM Colcemid were applied simultaneously, the complementary distributions of MT-bundles and IF-skeins mimicked those in taxol alone. This ability of taxol to block Colcemid's effects was concentration dependent. Decreasing the taxol: Colcemid ratio allowed the depolymerization of MTs, which correlated with the formation of IF-cables.