It has been possible to specifically label rabbit skeletal muscle actin at Lys-237 with 2,4-pentanedione, producing an enamine. This reaction can be reversed with hydroxylamine. The modification can be carried out with actin in either the G- or F-forms and does not affect polymerization-depolymerization. The modification does affect, however, the interaction of tropomyosin (Tm) with the modified F-actin. In the absence of Ca2+ and Mg2+ (μ = 0.12), Tm failed to bind to the modified F-actin whereas it did bind to unmodified F-actin (1 Tm:7 actins). Tm binding could be restored under these conditions by the addition of either troponin (Tn), Mg2+, or Mg2+ and Ca2+. Under certain conditions, Tm alone has been shown to inhibit actin-activated heavy meromyosin (HMM)-Mg2+-ATPase. This inhibition did not occur with the modified F-actin even though Tm was bound (~1 Tm:7 actins). Even when Tn was added to this system (in the absence of Ca2+), no inhibition of ATPase could be observed. Thus, this modification appears to prevent F-actin·Tm from assuming the 'blocking' inhibitory position (conformation). In addition, Tn appears to enhance the activation of heavy meromyosin-Mg2+-ATPase by the modified F-actin·Tm complex whether Ca2+ is present or not. This state may be analogous to the potentiated state (Murray, J.M., Knox, M.K., Trueblood, C.E., and Weber, A. (1982) Biochemistry 27, 906-915) seen with myosin subfragment 1-saturated actin at low ATP levels. Thus, using modified and unmodified F-actin, it is possible to produce three Tm·actin states: off (F-actin·Tm), on (modified F-actin·Tm), and 'potentiated' (modified F-actin·Tm·Tn).
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - 1984|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology