Polymerization of actin in the absence and presence of cytochalasin B: problems of determining "critical concentration".
Various concentrations of actin (0.3 or 1 mM MgCl2, 1 mM ATP, 1 mM EGTA) reached their final degree of polymerization (measured by a pyrene dye attached to actin) earlier in the presence of cytochalasin B than in its absence. The curves relating concentrations of polymeric F-actin to total actin concentration were under these conditions highly nonlinear making an unambiguous extrapolation to zero F-actin concentration (to deduce the "critical concentration" of actin polymerization) impossible. The concentration of actin, above which polymerization occurred, was unaltered by cytochalasin B (although for reasons not yet understood the specific fluorescence intensity of polymerized actin was lower in the presence of cytochalasin B than in its absence). The results show that a distinct "critical concentration" of actin polymerization must not always be well defined.
D000199:Actins / Q000032:analysis*; D000818:Animals; D003571:Cytochalasin B / Q000032:analysis*; D008274:Magnesium / Q000378:metabolism; D015636:Magnesium Chloride; D011817:Rabbits; D013050:Spectrometry, Fluorescence
D000199:Actins; D015636:Magnesium Chloride; D003571:Cytochalasin B; D008274:Magnesium