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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 35 (1980), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The microsomal fraction of frog sciatic nerves was found to contain Ca2+- or Mg2+-dependent hydrolytic activity toward different nucleoside di-and triphosphates. In the presence of Ca2+ substrate specificity was in the order CTP 〉 UTP 〉 GTP 〉 ATP. When Mg2+ was used, the triphosphates were approximately equally good substrates. ATP hydrolytic activity was very similar with Ca2+ or Mg2+ as the cofactor, whereas Ca2+ was the more potent activator of hydrolysis of the other triphosphates tested. The preparation showed some activity toward the nucleoside diphosphates but none toward the monophosphates or p-nitrophenylphosphate. The enzymic properties of ATP hydrolysis were more closely studied. The hydrolysis was optimal at 18–24°C in the presence of 1 mm-Ca2+ or 1 mm-Mg2+. Ca2+- and Mg2+-ATP hydrolysis displayed pH maxima around 8.0–8.5 and 7.4–8.0, respectively. Vmax values for Ca2+- and Mg2+-ATP hydrolysis were similar: approx. 12 μmol Pi per h per mg protein with a Km value of approx. 0.05 mm. The ATP hydrolysis activity was inhibited by NaF but unaffected by ouabain, vanadate, cytochalasin B, and various drugs known to influence ATPase activity of mitochondria. Zn2+ stimulated the ATP hydrolysis activity at low concentrations (10-6–10-5m) and inhibited it at higher concentrations. The possibility that these observations account for stimulation and inhibition of axonal transport in frog sciatic nerves exposed to similar concentrations of Zn2+ is discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1439-6327
    Keywords: Acceleration ; Eccentric ; Concentric ; Isokinetic ; Method error
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A new computerized dynamometer (the SPARK System) is described. The system can measure concentric and eccentric muscle strength (torque) during linear or nonlinear acceleration or deceleration, isokinetic movements up to 400° · s−1, and isometric torque. Studies were performed to assess: I. validity and reproducibility of torque measurements; II. control of lever arm position; III. control of different velocity patterns; IV. control of velocity during subject testing; and, V. intra-individual reproducibility. No significant difference was found between torque values computed by the system and known torque values (p〉0.05). No difference was present between programmed and external measurement of the lever arm position. Accelerating, decelerating and isokinetic velocity patterns were highly reproducible, with differences in elapsed time among 10 trials being never greater than 0.001 s. Velocity during concentric and eccentric isokinetic quadriceps contractions at 30° · s−1, 120° · s−1 and 270° · s−1 never varied by more than 3° · s−1 among subjects (N=21). Over three days of testing, the overall error for concentric and eccentric quadriceps contraction peak torque values for 5 angular velocities between 30° · s−1 and 270° · s−1 ranged from 5.8% to 9.0% and 5.8% to 9.6% respectively (N=25). The results indicate that the SPARK System provides valid and reproducible torque measurements and strict control of velocity. In addition, the intra-individual error is in accordance with those reported for other similar devices.
    Type of Medium: Electronic Resource
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