title: Modification of Lys-237 on actin by 2,4-pentanedione. Alteration of the interaction of actin with tropomyosin.
abstract: 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+ (mu = 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 (approximately 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 X 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 X 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 X actin states: off (F-actin X Tm), on (modified F-actin X Tm), and "potentiated" (modified F-actin X Tm X Tn).
mesh_terms: D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase; D002250:Carbon Radioisotopes; D002942:Circular Dichroism; D007659:Ketones / Q000494:pharmacology*; D008239:Lysine; D009132:Muscles / Q000378:metabolism*; D010422:Pentanones / Q000494:pharmacology*; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D013056:Spectrophotometry, Ultraviolet; D014335:Tropomyosin / Q000378:metabolism*
chemical_list: D000199:Actins; D002250:Carbon Radioisotopes; D007659:Ketones; D010422:Pentanones; D014335:Tropomyosin; C008790:acetylacetone; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D008239:Lysine