The binding of fluorescent phallotoxins to actin in myofibrils.
Fluorescence microscope observation of myofibrils incubated with rhodamine-phalloidin and coumarine-phallacidin showed an initial appearance of fluorescence bands at the Z-lines and near the middle of the sarcomeres indicating preferential binding of dye to actin subunits located at both actin filament ends. After long incubation times (1-3 h) however, a final pattern is reached which consists of fluorescent Z-lines in the center of uniformly labelled actin bands, with greater fluorescence in the Z-lines than in the uniform region outside the Z-lines. Increasing the temperature or the ionic strength increased the rate of change to the final pattern. These data indicate: (1) that the ends of the actin filament are kinetically more accessible to phallotoxins; (2) at long times when equilibrium binding presumably occurs, the concentration of actin subunits in the Z-band is greater than in the rest of the sarcomere.
Szczesna
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Muscle Research Group, Boston Biomedical Research Institute, MA 02114.
Lehrer
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D000199:Actins / Q000032:analysis* / Q000378:metabolism*; D000546:Amanitins / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D008856:Microscopy, Fluorescence; D009132:Muscles / Q000737:chemistry* / Q000378:metabolism; D009210:Myofibrils / Q000737:chemistry / Q000378:metabolism; D011817:Rabbits; D012518:Sarcomeres / Q000737:chemistry / Q000378:metabolism
D000199:Actins; D000546:Amanitins; C018358:phallotoxin