[Interaction of aldolase with thin filaments within I-disks, isolated from skeletal muscles]

Using electron microscopy and optical diffraction, Ca2+-dependent binding of a glycolytic enzyme (aldolase) to thin filaments of isolated skeletal muscle I-disks have been revealed. On the micrographs of negatively stained I-disks the cross-striation determined by troponin-tropomyosin complex distribution has a period of about 38 nm. The width of troponin-tropomyosin stripes is 5-6 nm. On the optical diffraction patterns from isolated I-disks the meridional reflections measuring 38.5, 19.2, 12.8 nm are present. On the micrographs of isolated I-disks, treated with aldolase in the absence of Ca2+ (1 mM EGTA) the width of periodic transverse stripes (period approximately 38 nm) increases from 5-6 nm to 25-28 nm due to the interaction of aldolase with thin filaments. On the optical diffraction patterns from I-disks treated with aldolase in the absence of Ca2+ (1 mM EGTA) the strong meridional reflection equal to 38.5 nm is present, while the reflections equal to 19.2 nm are absent. The optical diffraction patterns from I-disks treated with aldolase in the presence of Ca2+ (greater than or equal to 10(-5) M) do not, as a rule, differ from those obtained from I-disks not treated with aldolase, i.e. they contain the three above reflections. The binding of aldolase to thin filaments in the absence of Ca2+ is the reason of disappearance of meridional reflections equal to 19.2 and 12.8 nm.