Potentiated state of the tropomyosin actin filament and nucleotide-containing myosin subfragment 1.
The main purpose of this study was to determine whether potentiation of acto-S-1 ATPase activity (activity higher than that obtained with tropomyosin-free actin) could be caused by nucleotide-containing acto-S-1 complexes. In addition, we wanted to know whether these complexes also have a positive cooperative effect on their own apparent binding constant under conditions where nucleotide-free acto-S-1 complexes cause potentiation of ATPase activity. Using calcium-saturated troponin-tropomyosin actin filaments, we observed potentiation of ATPase activity in the presence of 5.0 mM magnesium 5'-adenylyl imidodiphosphate (MgAMPPNP) and calculated that the ability of acto-S-1-AMPPNP complexes to cause potentiation must have been very similar to that of nucleotide-free acto-S-1 complexes. In extension of earlier studies, potentiated acto-S-1 ATPase activity was characterized by an increase in Vmax and, as observed before, a lowering of the apparent Km for subfragment 1 (S-1). Under conditions similar to those that produce the potentiation of acto-S-1 ATPase activity, the apparent actin binding constant of nucleotide-free S-1 was increased about 3-5 fold while the apparent binding constant of AMPPNP to actin-bound S-1 was reduced to (2.5-10) x 10(2) M-1 compared to that of about (1-5) x 10(3) M-1 for S-1 bound to tropomyosin-free actin. Under the same conditions, the apparent binding constant of S-1-AMPPNP to actin was not increased. We suggest that a potentiated state of the tropomyosin actin filament is produced by the cooperative action of acto-S-1 or acto-S-1-AMPPNP complexes. The potentiated state is characterized by an increase in the Vmax of the acto-S-1 ATPase activity, increased binding constants for S-1 and S-1-ADP, and increased binding of tropomyosin to actin.
D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D003599:Cytoskeleton / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D046911:Macromolecular Substances; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011817:Rabbits; D014335:Tropomyosin / Q000378:metabolism*
D000199:Actins; D046911:Macromolecular Substances; D015879:Myosin Subfragments; D010446:Peptide Fragments; D014335:Tropomyosin; D000266:Adenylyl Imidodiphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins