title: Interaction of cytochalasin D with actin filaments in the presence of ADP and ATP.
abstract: Cytochalasin D strongly inhibits the faster components in the reactions of actin filament depolymerization and elongation in the presence of 10 mM Tris-Cl-, pH 7.8, 0.2 mM dithiothreitol, 1 mM MgCl2, 0.1 mM CaCl2, and 0.2 mM ATP or ADP. Assuming an exclusive and total capping of the barbed end by the drug, the kinetic parameters derived at saturation by cytochalasin D refer to the pointed end and are 10-15-fold lower than at the barbed end. In ATP, the critical concentration increases with cytochalasin D up to 12-fold its value when both ends are free; as a result of the lowering of the free energy of nucleation by cytochalasin D, short oligomers of F-actin exist just above and below the critical concentration. Cytochalasin D interacts strongly with the barbed ends independently of the ADP-G-actin concentration (K = 0.5 nM-1). In contrast, the affinity of cytochalasin D decreases cooperatively with increasing ATP-G-actin concentration. These data are equally well accounted for by two different models: either cytochalasin D binds very poorly to ATP-capped filament ends whose proportion increases with actin concentration, or cytochalasin D binds equally well to ATP-ends and ADP-ends and also binds to actin dimers in ATP but not in ADP. A linear actin concentration dependence of the rate of growth was found at the pointed end, consistent with the virtual absence of an ATP cap at that end.
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects* / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D015638:Cytochalasin D; D003572:Cytochalasins / Q000378:metabolism / Q000494:pharmacology*; D003599:Cytoskeleton / Q000187:drug effects*; D003864:Depression, Chemical; D007700:Kinetics; D008954:Models, Biological
chemical_list: D000199:Actins; D003572:Cytochalasins; D015638:Cytochalasin D; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate