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  • Title: Pig platelet tropomyosin: interactions with the other thin-filament proteins.
    Author: Pruliere G, Fuller SD, Weeds AG, d'Albis A, der Terrossian E.
    Journal: J Mol Biol; 1986 Dec 20; 192(4):815-30. PubMed ID: 2953902.
    Abstract:
    Pig platelet tropomyosin exhibits many of the functional activities of skeletal tropomyosin. At low ionic strength it forms end-to-end aggregates similar to those formed by skeletal tropomyosins. It forms a 1:1 complex with muscle troponin or with a troponin I-pig brain calmodulin complex, as well as a 1:6 association with platelet filamentous actin. Electron microscopy of paracrystals shows that the troponin binding site is slightly C-terminal of the unique cysteine, corresponding to position 190 of the rabbit skeletal alpha-tropomyosin sequence. The effect of a complex comprising platelet actin and tropomyosin on the ATPase activity of rabbit skeletal muscle myosin subfragment-1 was similar to that displayed by its skeletal muscle counterpart. Platelet tropomyosin decreased the activity by roughly half in a calcium-independent manner. Addition of troponin to the actin-tropomyosin in the absence of calcium results in further inhibition and allows the full activity of the complex to be restored by Ca2+. These results differ from those obtained by Côté & Smillie for horse platelet tropomyosin and this may reflect the different isomeric nature of pig platelet tropomyosin. These results suggest that the functional properties of non-muscle tropomyosins may differ when comparisons are made between proteins isolated from the same type of cell but in different species. Differences in self-association and actin-binding properties may be finely graded between different isoforms.
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