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T Irving

Publications and source records attributed to T Irving.

9 recordsLinked to original sources
PubMed2003

Modelling muscle motor conformations using low-angle X-ray diffraction.

New results on myosin head organization using analysis of low-angle X-ray diffraction patterns from relaxed insect flight muscle (IFM) from a giant waterbug, building on previous studies of myosin filaments in bony fish skeletal muscle (BFM), show that the information content of such low-angle diffraction patterns is very high despite the 'crystallographically low' resolution limit (65 A) of the spacings of the Bragg diffraction peaks being used. This high information content and high structural sensitivity arises because: (i) the atomic structures of the domains of the myosin head are known from protein crystallography; and (ii) myosin head action appears to consist mainly of pivoting between domains which themselves stay rather constant in structure, thus (iii) the intensity distribution among diffraction peaks in even the low resolution diffraction pattern is highly determined by the high-resolution distribution of atomically modelled domain mass. A single model was selected among 5000+ computer-generated variations as giving the best fit for the 65 reflections recorded within the selected resolution limit of 65 A. Clear evidence for a change in shape of the insect flight muscle myosin motor between the resting (probably like the pre-powerstroke) state and the rigor state (considered to mimic the end-of-powerstroke conformation) has been obtained. This illustrates the power of the low-angle X-ray diffraction method. The implications of these new results about myosin motor action during muscle contraction are discussed.

Journal Article↗
PubMed2001

Changes in myofibrillar structure and function produced by N-terminal deletion of the regulatory light chain in Drosophila.

The similarity of amino acid sequence and motifs of the N-terminal extensions of certain class II myosin light chains, found throughout the animal kingdom, suggest a common functional role. One possible role of the N-terminal extension is to enhance oscillatory work and power production in striated muscles that normally operate in an oscillatory mode. We conducted small-angle X-ray diffraction experiments and small-length-perturbation analysis to examine the structural and functional consequences of deleting the N-terminal extension of the myosin regulatory light chain (RLC) in Drosophila flight muscle. The in vivo lattice spacing of dorsal longitudinal muscle (DLM) of flies lacking the RLC N-terminal extension (Dmlc2delta2-46) was approximately 1 nm less than that of wild type (48.56 +/- 0.02 nm). The myofilament lattice of detergent-treated, demembranated DLM swelled, with the DmlcdeltaA2-46 lattice expanding more than wild type and requiring roughly twice the concentration of Dextran T500 to restore its lattice to in vivo spacing (9-10% vs. 4% w/v). The calcium sensitivity and maximum amplitude of net oscillatory work near the in vivo lattice spacing was significantly lower in Dmlc2delta2-46 compared to wild type (pCa50 shifted by approximately one-third of a pCa unit; amplitude reduced by approximately one-half). These changes were in contrast to the lack of effect reported in a previous study carried out in the absence of Dextran T500. The results are consistent with the N-terminal extension interacting with actin to increase the probability that crossbridges form during stretch-activated oscillatory work and power production, especially at submaximal levels of calcium activation.

Animals↗
PubMed1994

X-ray diffraction measurements of the extensibility of actin and myosin filaments in contracting muscle.

We have used a small angle scattering system assembled on the high flux multipole wiggler beam line at CHESS (Cornell) to make very accurate spacing measurements of certain meridional and layer-line reflections from contracting muscles. During isometric contraction, the actin 27.3 A reflection increases in spacing from its resting value by approximately 0.3%, and other actin reflections, including the 59 and 51 A off-meridional reflections, show corresponding changes in spacing. When tension is augmented or diminished by applying moderate speed length changes to a contracting muscle, changes in spacing in the range of 0.19-0.24% (when scaled to full isometric tension) can be seen. The larger difference between the resting and isometric spacings suggests either nonlinearity at low tension levels or the presence of a component related to activation itself. Myosin filaments also show similar increases in axial period during slow stretch, in addition to the well known larger change associated with activation. An actin spacing change of 0.25-0.3% can also be measured during a 2 ms time frame immediately after a quick release, showing that the elastic behavior is rapid. These observations of filament extensions totaling 2-3 nm per half-sarcomere may necessitate some significant revision of the interpretation of a number of mechanical experiments in muscle, in which it has usually been assumed that virtually all of the elasticity resides in the cross-bridges.

Actins↗
PubMed1993

Towards the measurement of ideal data for macromolecular crystallography using synchrotron sources.

Synchrotron radiation has been used extensively to overcome a variety of technical challenges involved in data collection from macromolecular crystals. The next generation of such sources offer a higher brilliance at much shorter wavelengths than hitherto available. Hence, the quality of X-ray diffraction data from crystals of biological macromolecules will be further improved in terms of reduced systematic and random errors, in conjunction with a very high degree of completeness of, and multiple measurements within, the data set. Real data sets should be able to approach closely the quality of ideal data sets. Tests at CHESS are described of the feasibility of recording protein crystal diffraction patterns at ultra-short wavelengths (lambda = 0.3 A) and very-short wavelengths (lambda = 0.5 A), in monochromatic rotating crystal geometry.

Journal Article↗
PubMedDate not supplied

A comparison of four methods of normal newborn temperature measurement.

PURPOSE: The purpose of this study was to: (a) compare newborn temperature measurements obtained by digital disposable, electronic, and tympanic thermometers with glass mercury thermometers, and (b) compare financial implications of each method. METHODS: In this correlational study, 12 perinatal and neonatal nurses obtained temperature measurements of 184 newborns between 1 and 168 hours of age. The stratified convenience sample was selected using medical records numbers. Temperature instruments included glass thermometer, tympanic thermometer, electronic thermometer, and a digital thermometer. Data were analyzed by Pearson r coefficients, mean, standard deviation, and range using an SPSS statistical package. RESULTS: The glass thermometer, electronic thermometer, and digital thermometer temperature assessments were highly correlated (0.748-1.0). The tympanic thermometer had a low correlation coefficient (0.35). Use of the glass thermometer had the highest accompanying cost. Tympanic thermometers were the most cost effective. CLINICAL IMPLICATIONS: In healthy newborns, the use of electronic and digital thermometers can be encouraged if there is concern about using glass thermometers. These results cannot be extrapolated to sick infants. While tympanic thermometers had the lowest associated cost, their lack of correlation with the gold standard glass thermometers for accurate temperature assessment makes them a poor choice for healthy newborns.

Body Temperature↗