Summary
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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∼106M−1) and subsequently a second with lower affinity (K∼102–104 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.
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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.
Zusammenfassung
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1.
In 3 verschiedenen Methoden zeigte sich, daß Mg-ADP in 2 Schritten an Myosin aus Herz- und schnell kontrahierenden Skelettmuskeln bindet. 1 Mol Mg-ADP bindet mit hoher Affinität (K∼106 M−1) und darauf ein zweites mit niederer Affinität (K∼102–104 M−1) pro Myosin. Nur 1 Mol Mg-ADP bindet mit hoher Affinität an isolierte Myosinköpfe. Dies deutet auf negative Kooperativität zwischen den beiden Bindungsstellen in intaktem Myosin.
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2.
In Gegenwart von Nukleotiden zeigen die beiden Köpfe eines Myosin-moleküls verschiedene Konformationen, da an jedem Kopf eine andere essentielle Thiolgruppe leicht mit N-Aethylmaleinimid reagiert. In Gegenwart von Mg-Pyrophosphat reagiert an beiden Myosinköpfen eine Thiol-1-Gruppe besonders leicht. Der Nukleosidanteil scheint für diese zweite Art von Wechselwirkung zwischen den beiden Myosinköpfen verantwortlich zu sein.
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This work was supported by SNSF grant 3.675.75.
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Schaub, M.C., Watterson, J.G. & Waser, P.G. Evidence for head-head interactions in myosin from cardiac and skeletal muscles. Basic Res Cardiol 72, 124–132 (1977). https://doi.org/10.1007/BF01906350
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DOI: https://doi.org/10.1007/BF01906350